an essay on sleep

Why sleep is important

Sleep is essential for a person’s health and wellbeing, according to the National Sleep Foundation (NSF). Yet millions of people do not get enough sleep and many suffer from lack of sleep. For example, surveys conducted by the NSF (1999-2004) reveal that at least 40 million Americans suffer from over 70 different sleep disorders and 60 percent of adults report having sleep problems a few nights a week or more. Most of those with these problems go undiagnosed and untreated. In addition, more than 40 percent of adults experience daytime sleepiness severe enough to interfere with their daily activities at least a few days each month — with 20 percent reporting problem sleepiness a few days a week or more. Furthermore, 69 percent of children experience one or more sleep problems a few nights or more during a week.

According to psychologist and sleep expert David F. Dinges, Ph.D., of the Division of Sleep and Chronobiology and Department of Psychiatry at the University of Pennsylvania School of Medicine, irritability, moodiness and disinhibition are some of the first signs a person experiences from lack of sleep . If a sleep-deprived person doesn’t sleep after the initial signs, said Dinges, the person may then start to experience apathy, slowed speech and flattened emotional responses, impaired memory and an inability to be novel or multitask. As a person gets to the point of falling asleep, he or she will fall into micro sleeps (5-10 seconds) that cause lapses in attention, nod off while doing an activity like driving or reading and then finally experience hypnagogic hallucinations, the beginning of REM sleep. (Dinges, Sleep, Sleepiness and Performance , 1991)

Everyone’s individual sleep needs vary. In general, most healthy adults are built for 16 hours of wakefulness and need an average of eight hours of sleep a night. However, some individuals are able to function without sleepiness or drowsiness after as little as six hours of sleep. Others can't perform at their peak unless they've slept ten hours. And, contrary to common myth, the need for sleep doesn't decline with age but the ability to sleep for six to eight hours at one time may be reduced. (Van Dongen & Dinges, Principles & Practice of Sleep Medicine , 2000)

Psychologists and other scientists who study the causes of sleep disorders have shown that such problems can directly or indirectly be tied to abnormalities in the following systems:

Physiological systems

Brain and nervous system

Cardiovascular system

Metabolic functions

Immune system

Furthermore, unhealthy conditions, disorders and diseases can also cause sleep problems, including:

Pathological sleepiness, insomnia and accidents

Hypertension and elevated cardiovascular risks (MI, stroke)

Emotional disorders (depression, bipolar disorder)

Obesity; metabolic syndrome and diabetes

Alcohol and drug abuse (Dinges, 2004)

Groups that are at particular risk for sleep deprivation include night shift workers, physicians (average sleep = 6.5 hours a day; residents = 5 hours a day), truck drivers, parents and teenagers. (American Academy of Sleep Medicine and National Heart, Lung, and Blood Institute Working Group on Problem Sleepiness. 1997).

Stress is the number one cause of short-term sleeping difficulties , according to sleep experts. Common triggers include school- or job-related pressures, a family or marriage problem and a serious illness or death in the family. Usually the sleep problem disappears when the stressful situation passes. However, if short-term sleep problems such as insomnia aren't managed properly from the beginning, they can persist long after the original stress has passed.

Drinking alcohol or beverages containing caffeine in the afternoon or evening, exercising close to bedtime, following an irregular morning and nighttime schedule, and working or doing other mentally intense activities right before or after getting into bed can disrupt sleep.

If you are among the 20 percent of employees in the United States who are shift workers, sleep may be particularly elusive. Shift work forces you to try to sleep when activities around you — and your own "biological rhythms" — signal you to be awake. One study shows that shift workers are two to five times more likely than employees with regular, daytime hours to fall asleep on the job.

Traveling also disrupts sleep, especially jet lag and traveling across several time zones. This can upset your biological or “circadian” rhythms.

Environmental factors such as a room that's too hot or cold, too noisy or too brightly lit can be a barrier to sound sleep. And interruptions from children or other family members can also disrupt sleep. Other influences to pay attention to are the comfort and size of your bed and the habits of your sleep partner. If you have to lie beside someone who has different sleep preferences, snores, can't fall or stay asleep, or has other sleep difficulties, it often becomes your problem too!

Having a 24/7 lifestyle can also interrupt regular sleep patterns: the global economy that includes round the clock industries working to beat the competition; widespread use of nonstop automated systems to communicate and an increase in shift work makes for sleeping at regular times difficult.

A number of physical problems can interfere with your ability to fall or stay asleep. For example, arthritis and other conditions that cause pain, backache, or discomfort can make it difficult to sleep well.

Epidemiological studies suggest self-reported sleep complaints are associated with an increased relative risk of cardiovascular morbidity and mortality. For women, pregnancy and hormonal shifts including those that cause premenstrual syndrome (PMS) or menopause and its accompanying hot flashes can also intrude on sleep.

Finally, certain medications such as decongestants, steroids and some medicines for high blood pressure, asthma, or depression can cause sleeping difficulties as a side effect.

It is a good idea to talk to a physician or mental health provider about any sleeping problem that recurs or persists for longer than a few weeks.

According to the DSM, some psychiatric disorders have fatigue as a major symptom. Included are: major depressive disorder (includes postpartum blues), minor depression , dysthymia, mixed anxiety-depression, seasonal affective disorder and bipolar disorder .

According to a long-term study published in the 2004 April issue of Alcoholism: Clinical and Experimental Research , young teenagers whose preschool sleep habits were poor were more than twice as likely to use drugs, tobacco or alcohol. This finding was made by the University of Michigan Health System as part of a family health study that followed 257 boys and their parents for 10 years. The study found a significant connection between sleep problems in children and later drug use, even when other issues such as depression, aggression, attention problems and parental alcoholism were taken into account. Long-term data on girls isn't available yet. The researchers suggest that early sleep problems may be a "marker" for predicting later risk of early adolescent substance abuse — and that there may be a common biological factor underlying both traits. Although the relationship between sleep problems and the abuse of alcohol in adults is well known, this is the first study to look at the issue in children.

Nightmares are dreams with vivid and disturbing content. They are common in children during REM sleep. They usually involve an immediate awakening and good recall of the dream content.

Sleep terrors are often described as extreme nightmares. Like nightmares, they most often occur during childhood, however they typically take place during non-REM (NREM) sleep. Characteristics of a sleep terror include arousal, agitation, large pupils, sweating, and increased blood pressure. The child appears terrified, screams and is usually inconsolable for several minutes, after which he or she relaxes and returns to sleep. Sleep terrors usually take place early in the night and may be combined with sleepwalking. The child typically does not remember or has only a vague memory of the terrifying events.

In the August 2004 issue of the journal Sleep , Dr. Timothy Roehrs, the Director of research at the Sleep Disorders and Research Center at Henry Ford Hospital in Detroit published one of the first studies to measure the effect of sleepiness on decision making and risk taking. He found that sleepiness does take a toll on effective decision making.

Cited in the October 12, New York Times Science section, Dr. Roehrs and his colleagues paid sleepy and fully alert subjects to complete a series of computer tasks. At random times, they were given a choice to take their money and stop. Or they could forge ahead with the potential of either earning more money or losing it all if their work was not completed within an unknown remainder of time.

Dr. Roehrs found that the alert people were very sensitive to the amount of work they needed to do to finish the tasks and understood the risk of losing their money if they didn't. But the sleepy subjects chose to quit the tasks prematurely or they risked losing everything by trying to finish the task for more money even when it was 100 percent likely that they would be unable to finish, said Dr. Roehrs.

According to the National Commission on Sleep Disorders Research (1998) and reports from the National Highway Safety Administration (NHSA)(2002), high-profile accidents can partly be attributed to people suffering from a severe lack of sleep.

Each year the cost of sleep disorders, sleep deprivation and sleepiness, according to the NCSDR, is estimated to be $15.9 million in direct costs and $50 to $100 billion a year in indirect and related costs. And according to the NHSA, falling asleep while driving is responsible for at least 100,000 crashes, 71,000 injuries and 1,550 deaths each year in the United States. Young people in their teens and twenties, who are particularly susceptible to the effects of chronic sleep loss, are involved in more than half of the fall-asleep crashes on the nation's highways each year. Sleep loss also interferes with the learning of young people in our nation's schools, with 60 percent of grade school and high school children reporting that they are tired during the daytime and 15 percent of them admitting to falling asleep in class.

According to the Department of Transportation (DOT), one to four percent of all highway crashes are due to sleepiness, especially in rural areas and four percent of these crashes are fatal.

Risk factors for drowsy driving crashes:

Late night/early morning driving

Patients with untreated excessive sleepiness

People who obtain six or fewer hours of sleep per day

Young adult males

Commercial truck drivers

Night shift workers

Medical residents after their shift

According to sleep researchers, a night's sleep is divided into five continually shifting stages, defined by types of brain waves that reflect either lighter or deeper sleep. Toward morning, there is an increase in rapid eye movement, or REM sleep, when the muscles are relaxed and dreaming occurs, and recent memories may be consolidated in the brain. The experts say that hitting a snooze alarm over and over again to wake up is not the best way to feel rested. “The restorative value of rest is diminished, especially when the increments are short,” said psychologist Edward Stepanski, PhD who has studied sleep fragmentation at the Rush University Medical Center in Chicago. This on and off again effect of dozing and waking causes shifts in the brain-wave patterns. Sleep-deprived snooze-button addicts are likely to shorten their quota of REM sleep, impairing their mental functioning during the day. ( New York Times , October 12, 2004)

Certain therapies, like cognitive behavioral therapy teach people how to recognize and change patterns of thought and behavior to solve their problems. Recently this type of therapy has been shown to be very effective in getting people to fall asleep and conquer insomnia.

According to a study published in the October 2004 issue of The Archives of Internal Medicine , cognitive behavior therapy is more effective and lasts longer than a widely used sleeping pill, Ambien, in reducing insomnia. The study involved 63 healthy people with insomnia who were randomly assigned to receive Ambien, the cognitive behavior therapy, both or a placebo. The patients in the therapy group received five 30-minute sessions over six weeks. They were given daily exercises to “recognize, challenge and change stress-inducing” thoughts and were taught techniques, like delaying bedtime or getting up to read if they were unable to fall asleep after 20 minutes. The patients taking Ambien were on a full dose for a month and then were weaned off the drug. At three weeks, 44 percent of the patients receiving the therapy and those receiving the combination therapy and pills fell asleep faster compared to 29 percent of the patients taking only the sleeping pills. Two weeks after all the treatment was over, the patients receiving the therapy fell asleep in half the time it took before the study and only 17 percent of the patients taking the sleeping pills fell asleep in half the time. (New York Times, October 5, 2004)

According to leading sleep researchers, there are techniques to combat common sleep problems:

Keep a regular sleep/wake schedule

Don’t drink or eat caffeine four to six hours before bed and minimize daytime use

Don’t smoke, especially near bedtime or if you awake in the night

Avoid alcohol and heavy meals before sleep

Get regular exercise

Minimize noise, light and excessive hot and cold temperatures where you sleep

Develop a regular bed time and go to bed at the same time each night

Try and wake up without an alarm clock

Attempt to go to bed earlier every night for certain period; this will ensure that you’re getting enough sleep

In clinical settings, cognitive-behavior therapy (CBT) has a 70-80 percent success rate for helping those who suffer from chronic insomnia. Almost one third of people with insomnia achieve normal sleep and most reduce their symptoms by 50 percent and sleep an extra 45-60 minutes a night. When insomnia exists along with other psychological disorders like depression, say the experts, the initial treatment should address the underlying condition.

But sometimes even after resolving the underlying condition, the insomnia still exists, says psychologist Jack Edinger, PhD, of the VA Medical Center in Durham, North Carolina and Professor of Psychiatry and Behavioral Sciences at Duke University and cautions that treating the depression usually doesn’t resolve the sleep difficulties. From his clinical experience, he has found that most patients with insomnia should be examined for specific behaviors and thoughts that may perpetuate the sleep problems. When people develop insomnia, they try to compensate by engaging in activities to help them get more sleep. They sleep later in the mornings or spend excessive times in bed. These efforts usually backfire, said Edinger.

From his clinical work and research on sleep, psychologist Charles M. Morin, PhD, a Professor in the Psychology Department and Director of the Sleep Disorders Center at University Laval in Quebec, Canada says that ten percent of adults suffer from chronic insomnia. In a study released in the recent issue of Sleep Medicine Alert published by the NSF, Morin outlines how CBT helps people overcome insomnia. Clinicians use sleep diaries to get an accurate picture of someone’s sleep patterns. Bedtime, waking time, time to fall asleep, number and durations of awakening, actual sleep time and quality of sleep are documented by the person suffering from insomnia.

A person can develop poor sleep habits (i.e. watching TV in bed or eating too much before bedtime), irregular sleep patterns (sleeping too late, taking long naps during the day) to compensate for lost sleep at night. Some patients also develop a fear of not sleeping and a pattern of worrying about the consequences of not sleeping, said Morin. “Treatments that address the poor sleep habits and the faulty beliefs and attitudes about sleep work but sometimes,” said Morin, “medication may play a role in breaking the cycle of insomnia. But behavioral therapies are essential for patients to alter the conditions that perpetuate it.”

CBT attempts to change a patient’s dysfunctional beliefs and attitudes about sleep. “It restructure thoughts — like, ‘I’ve got to sleep eight hours tonight’ or ‘I’ve got to take medication to sleep’ or ‘I just can’t function or I’ll get sick if I don’t sleep.’ These thoughts focus too much on sleep, which can become something like performance anxiety — sleep will come around to you when you’re not chasing it,” said Edinger.

What works in many cases, said Morin and Edinger, is to standardize or restrict a person’s sleep to give a person more control over his or her sleep. A person can keep a sleep diary for a couple of weeks and a clinician can monitor the amount of time spent in bed to the actual amount of time sleeping. Then the clinician can instruct the patient to either go to bed later and get up earlier or visa versa. This procedure improves the length of sleeping time by imposing a mild sleep deprivation situation, which has the result of reducing the anxiety surrounding sleep. To keep from falling asleep during the day, patients are told not to restrict sleep to less than five hours.

Standardizing sleep actually helps a person adjust his or her homeostatic mechanism that balances sleep, said Edinger. “Therefore, if you lose sleep, your homeostatic mechanism will kick in and will work to increase the likelihood of sleeping longer and deeper to promote sleep recovery. This helps a person come back to their baseline and works for the majority.”

A person can also establish more stimulus control over his or her bedroom environment, said Morin. This could include: going to bed only when sleepy, getting out of bed when unable to sleep, prohibiting non-sleep activities in the bedroom, getting up at the same time every morning (including weekends) and avoiding daytime naps.

Finally, a person can incorporate relaxation techniques as part of his or her treatment. For example, a person can give herself or himself an extra hour before bed to relax and unwind and time to write down worries and plans for the following day.

In CBT, said Morin, breaking the thought process and anxiety over sleep is the goal. “After identifying the dysfunctional thought patterns, a clinician can offer alternative interpretations of what is getting the person anxious so a person can think about his or her insomnia in a different way.” Morin offers some techniques to restructure a person’s cognitions. “Keep realistic expectations, don’t blame insomnia for all daytime impairments, do not feel that losing a night’s sleep will bring horrible consequences, do not give too much importance to sleep and finally develop some tolerance to the effects of lost sleep.

According to Edinger, aging weakens a person’s homeostatic sleep drive after age 50. Interestingly, the length of the circadian cycle stays roughly the same over the lifespan but the amplitude of the circadian rhythm may decline somewhat with aging.

National Sleep Foundation http://www.thensf.org

American Academy of Sleep Medicine http://www.aasmnet.org/

American Insomnia Association http://www.americaninsomniaassociation.org/

Sleep Research Society http://www.sleepresearchsociety.org/

NIH National Center for Sleep Disorders Research http://www.nhlbi.nih.gov/sleep

The MayoClinic.com Sleep Center

(Blake, et al, Psychological Reports, 1998; National Heart, Lung and Blood Institute Working Group on Insomnia, 1998)

David F. Dinges, PhD , Professor of Psychology in Psychiatry, Chief, Division of Sleep and Chronobiology, University of Pennsylvania School of Medicine

Jack Edinger, PhD , of the VA Medical Center in Durham, North Carolina and Professor of Psychiatry and Behavioral Sciences at Duke University

Charles M. Morin, PhD , a Professor in the Psychology Department and Director of the Sleep Disorders Center at University Laval in Quebec, Canada

Timothy Roehrs, PhD , the Director of Research, Sleep Disorders and Research Center at Henry Ford Hospital

Edward Stepanski, PhD , who has studied sleep fragmentation at the Rush University Medical Center in Chicago

Related Reading

• Getting a good night’s sleep: How psychologists help with insomnia
• What to Do When You Dread Your Bed

Loading metrics

Open Access

Essays articulate a specific perspective on a topic of broad interest to scientists.

See all article types »

The new science of sleep: From cells to large-scale societies

Contributed equally to this work with: Omer Sharon, Eti Ben Simon

Roles Conceptualization, Visualization, Writing – original draft, Writing – review & editing

Affiliations Department of Psychology, University of California, Berkeley, California, United States of America, Helen Wills Neuroscience Institute, University of California, Berkeley, California, United States of America

Roles Visualization, Writing – original draft, Writing – review & editing

Roles Writing – original draft, Writing – review & editing

Roles Conceptualization, Supervision, Writing – original draft, Writing – review & editing

* E-mail: [email protected]

• Omer Sharon, 
• Eti Ben Simon, 
• Vyoma D. Shah, 
• Tenzin Desel, 
• Matthew P. Walker

Published: July 8, 2024

• https://doi.org/10.1371/journal.pbio.3002684
• Reader Comments

In the past 20 years, more remarkable revelations about sleep and its varied functions have arguably been made than in the previous 200. Building on this swell of recent findings, this essay provides a broad sampling of selected research highlights across genetic, molecular, cellular, and physiological systems within the body, networks within the brain, and large-scale social dynamics. Based on this raft of exciting new discoveries, we have come to realize that sleep, in this moment of its evolution, is very much polyfunctional (rather than monofunctional), yet polyfunctional for reasons we had never previously considered. Moreover, these new polyfunctional insights powerfully reaffirm sleep as a critical biological, and thus health-sustaining, requisite. Indeed, perhaps the only thing more impressive than the unanticipated nature of these newly emerging sleep functions is their striking divergence, from operations of molecular mechanisms inside cells to entire group societal dynamics.

Citation: Sharon O, Ben Simon E, Shah VD, Desel T, Walker MP (2024) The new science of sleep: From cells to large-scale societies. PLoS Biol 22(7): e3002684. https://doi.org/10.1371/journal.pbio.3002684

Copyright: © 2024 Sharon et al. This is an open access article distributed under the terms of the Creative Commons Attribution License , which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

Funding: The author(s) received no specific funding for this work.

Competing interests: The authors have declared that no competing interests exist.

Abbreviations: ADHD, attention deficit hyperactivity disorder; ASD, autism spectrum disorder; CSF, cerebrospinal fluid; DORA, dual orexin receptor antagonist; EEG, electroencephalogram; fMRI, functional MRI; HPA, hypothalamic-pituitary-adrenal; IRT, imagery rehearsal therapy; NREM, nonrapid eye movement; PTSD, posttraumatic stress disorder; RBD, REM behavior disorder; REM, rapid eye movement; SWA, slow-wave activity

Introduction

Sleep appears to be a universal, highly conserved state across the animal kingdom [ 1 , 2 ]. This fact would perhaps suggest a common single function of sleep that transcends phylogeny; however, proving this has been far more challenging than anticipated. Indeed, science has struggled to answer, with universal agreement, the basic question of why it is that we sleep and, to an ever greater degree in humans, why we dream. Yet, in the past 2 decades, more has arguably been uncovered about the polyfunctional nature of sleep than in the previous 200 years. Building on a wave of exciting recent discoveries, in this Essay, we provide a select collection of highlights from sleep research across genetic, molecular, cellular, whole body, whole brain, group-social, and societal levels.

This Essay is not meant to serve as a comprehensive review of sleep research nor an exhaustive cataloging of all recent discoveries. Rather, we aim to provide the reader with a sampling of representative new research areas. Towards that end, the Essay is structured into several main sections that traverse a descriptive narrative, from cells to society, each exploring different facets of sleep science. We start with recent discoveries at the level of DNA and genes, describing both genes that control sleep duration, and the newly revealed role of sleep in DNA repair. Thereafter, we ascend to physiological systems, one example of which focuses on very recent findings regarding an intimate and bidirectional link between sleep and the gut microbiome. Next, we address exciting recent work seeking to develop new technologies to augment and enhance human sleep, ranging from electrical to acoustic, kinesthetic, and thermal manipulations, all of which have marked therapeutic and intervention implications.

Having considered sleep functions within the body, we then move higher into the brain. We address novel sleep functions at the neural level, including sleep’s role in regulating the glymphatic cleansing system. Staying within the brain, we then address one of the newest emerging fields of sleep neuroscience, that of emotional wellness and mental health. Here, the latest findings move beyond sleep’s role in basic emotional regulation and, instead, signal a clear and intimate connection between sleep and complex socioemotional functions within an individual, between individuals, across large groups of individuals, and across entire societies.

Staying with the theme of sleep across groups, we then investigate sleep’s evolutionary roots across phylogenetic groups, providing a very different approach to understanding the functions of sleep. We describe new work that seeks to explain the vast, previously perplexing, and impressively large differences in sleep quantity and physiological sleep quality (Glossary) across species. From such an examination come powerful insights into the universal function(s) of sleep that only this type of approach can reveal. Finally, we move past the basic physiological state of sleep into the altered psychological state of human consciousness called dreaming. We outline both prior and the latest evidence regarding the functional importance of dreaming in service of memory enhancement, creativity, and emotional first aid, independent of the rapid eye movement (REM) sleep (Glossary) state such dreams emerge from.

Sleep quality.

Evaluated through both subjective means, which involves individual’s self-reporting their perceived quality of sleep, and objective methods, including measurements of sleep stages or quantitative electroencephalography brainwave metrics.

Rapid eye movement (REM) sleep.

Also referred to as paradoxical sleep, REM represents a sleep phase marked by a desynchronized electroencephalogram with high-frequency, low-amplitude activity (especially in the theta band), rapid movement of the eyes, muscle immobilization, and the occurrence of dreams.

Nonrapid eye movement (NREM) sleep.

Describes the sleep phase that encompasses the period between falling asleep and reaching deep sleep, yet is not REM sleep. The stages of NREM sleep are typically categorized into 3 categories: N1 (shallow sleep), N2 (light sleep), and N3 (deep sleep).

Slow-wave activity (SWA).

A characteristic electrophysiological pattern marked by slow, synchronized oscillations in the 0.5 to 4.0 Hz range. SWA reaches its peak during NREM sleep and diminishes across the night, reflecting the discharge of homeostatic sleep pressure that builds the longer an individual is awake.

Obstructive sleep apnea.

A sleep disorder characterized by recurrent impaired or absent breathing during sleep, as well as by reductions in blood oxygen saturation, caused by airway occlusion.

Sleep restriction.

A decrease (but not total absence) of sleep across the prior night or nights. Amounts typically range from 1 to 6 hours of sleep reduction. Sleep restriction is often termed chronic if it persists for more than 24 hours.

Gut dysbiosis.

An imbalance in the gut’s microbial community, potentially leading to health issues. It involves a decrease in beneficial bacteria and an increase in harmful ones, disrupting normal gut function. Restoring balance is crucial for overall health.

Disrupted sleep.

Irregular sleep patterns characterized by insufficient sleep duration, disrupted sleep cycles (such as altered sleep architecture), and/or reduced sleep quality (evaluated through measures like spectral electroencephalogram power).

Allostatic distress.

A state reflecting the cumulative physiological damage caused by chronic stress, in part stemming from prolonged activation of stress-related messengers like cortisol and adrenaline. Allostatic distress is associated with disruption of adaptive biological systems and responses, including those related to the hypothalamic-pituitary-adrenal (HPA) axis and immune function, ultimately contributing to various health issues.

Cognitive behavioral therapy for insomnia.

A scientifically supported approach to treating insomnia that involves a comprehensive psychological intervention aimed at addressing the underlying behaviors and thought patterns associated with insomnia.

Functional connectivity.

Within functional MRI, the statistical association observed between activity signals originating from 2 or more anatomically separate brain regions.

Through these exciting new discoveries, and many others like them, we have come to recognize that sleep has evolved to support polyfunctional processes for the brain and body. Moreover, such powerful new evidence reaffirms sleep as a biologically critical and health-sustaining requisite—a requisite for reasons: that are surprising in their nature.

Genes linked to short sleep need

Insufficient sleep exacts a significant toll on all cognitive and emotional brain functions and impacts all major physiological systems of the body, from the immune, cardiovascular, thermoregulatory, metabolic, and reproductive systems, to respiratory and endocrine systems ( Fig 1 ). Unsurprisingly, then, insufficient sleep also predicts all-cause mortality risk [ 1 , 3 , 4 ]. Nevertheless, there is a common claim by some that, “I’m one of those individuals who can function just fine on 5 hours of sleep or less.” While this is unlikely, based on the extent of empirical findings [ 5 – 8 ], a select collection of individuals do seem to be exceptions to the recommended 7- to 9-hour sleep requirement, on the basis of gene mutations that reduce sleep need [ 5 ]. Termed “natural short sleepers,” this small set of individuals appears to have a natural sleep requisite as low as 6 to 6.25 hours per night without showing any observable cognitive deficits assessed so far [ 5 ].

• PPT PowerPoint slide
• PNG larger image
• TIFF original image

Sleep serves a multitude of functions for humans. These functions exist at multiple physiological levels, from cells (bottom panel) to bodily systems (left panel), through to multiple brain functions and systems (right panel).

https://doi.org/10.1371/journal.pbio.3002684.g001

The first genetic variant accounting for these natural short sleepers centered on a variation in DEC2 gene identified in families of naturally short-sleeping humans. Initial work focused on dizygotic twins, each of whom differed on the basis of this DEC2 gene variant (standard versus mutation). The twins had their daily sleep–wake patterns measured and also came to the sleep laboratory for full sleep physiological recordings. The data revealed that the twin with the DEC2 mutation naturally slept 30 to 60 minutes less than their noncarrier twin in both real-world and laboratory-assessed environments [ 9 ].

This was not the most interesting result, however. Following a 38-hour sleep deprivation period, the twin carrying the short-sleeping genetic variant exhibited greater resilience to sleep deprivation, defined by performance on select cognitive tasks, having only half the number of attentional failures compared to their noncarrier sibling. The final revelation emerged during the subsequent night of recovery sleep. Typically, following sleep loss, individuals sleep notably longer, indicating a buildup of sleep debt that is proportional to the amount of extended time awake. The longer the prior waking period, the longer and deeper the recovery sleep. However, the DEC2 mutant carrier did not show this normal strong sleep–rebound response, obtaining 1.5 hours less recovery sleep than their noncarrier twin. This finding once again indicates a reduced innate sleep need, here even under the pressure of prior sleep deprivation. Similar results have been observed in DEC2 mutant mice [ 5 ], with wild-type mice showing a 70% increase in NREM sleep (Glossary) following sleep deprivation, compared to a 17% increase in the DEC2 mutant mice.

How is short sleep achieved?

Using mice genetically engineered to carry the short-sleeping genes identified in humans, new findings have revealed how and why the DEC2 mutation may afford a reduced sleep need [ 7 , 8 ]. The DEC2 mutation results in an increased expression of the wake-promoting neurochemical, orexin [ 10 ]; i.e., natural short sleepers with the DEC2 variant have an amplified neurochemical wake–drive, resulting in prolonged wakefulness across the day and thus shorter sleep duration at night. However, this insight does not wholly explain the reduced homeostatic sleep need after sleep deprivation in individuals carrying the DEC2 mutation. If anything, a strong drive for wakefulness may be predicted to result in a stronger buildup of sleep homeostatic factors, such as adenosine, that would increase homeostatic sleep needs during postdeprivation recovery.

An additional explanation for the innate reduced general sleep amount (approximately 6 hours), and one that may account for a reduced homeostatic sleep need, concerns the electrical efficiency of deep-sleep brain waves. A physiological measure of deep NREM sleep quality is slow electrical brainwave activity, also known as slow-wave activity (SWA, <4 Hz; Glossary). In the aforementioned DEC2 twin studies, across all 3 nights recorded in the laboratory, the short-sleeping twin exhibited significantly greater SWA, one interpretation of which is that their deep NREM sleep was of superior electrical quality. By means of this superior SWA power, short-sleeping individuals may be able to dissipate the accumulation of sleep needs based on time awake during the day, and in doing so, reduce the total amount of time needed for sleep [ 9 ], thus increasing sleep efficiency and decreasing sleep need.

Another mutation has also been discovered in natural short sleepers. ADRB1 gene governs the beta-1 adrenergic receptor, which influences sleep–wake regulation. Much like the DEC2 mutation, those carrying the ADRB1 mutation display increased SWA during NREM sleep early in the night. Moreover, the speed of decline in SWA across the night—potentially reflecting a more efficient evacuation of accumulated sleep pressure across the waking day—was faster in those carrying this mutation. Again, this points to the possibility of superior deep-sleep electrical brainwave activity, increasing sleep efficiency and, hence, decreasing the amount of sleep needed [ 6 ].

This emerging picture of superior deep-sleep physiology in short sleepers is not, however, exclusive to NREM sleep. In several short-sleeping studies, alterations in REM sleep have also been identified, the reasons and function(s) of which are more mysterious; e.g., in the dizygotic DEC2 twin studies, following a sleep deprivation phase, the noncarrier twin spent nearly 2 additional hours in REM sleep during recovery sleep, as is typical. However, the carrier twin showed almost no change in the rebound of REM sleep [ 9 ], indicative of a reduced REM sleep need as well. Similarly, wild-type mice exhibit a 175% increase in REM sleep after sleep deprivation, yet short-sleeping DEC2 mutant mice expressed only a 74% relative increase in REM sleep [ 5 ]. ADRB1 short-sleeping mutant mice similarly do not show the same REM sleep need relative to wild-type mice under normal (nondeprived) sleeping conditions [ 6 ]. Short-sleeping gene variants, therefore, seem to require less total sleep, but also less REM sleep. There are still no clear answers as to why.

Is short sleep without true cost?

Arguably the most fundamental question in the emerging description of short sleep is that of cost—is there truly no health cost to these short-sleeping individuals? Cross-sectional analyses suggest that cognitive functions do not suffer, relative to controls without the DEC2 genetic variant, yet there have been no systematic studies assessing other known sleep-dependent brain and body functions ( Fig 1 ). Furthermore, no prospective longitudinal studies of natural short sleepers have been conducted to determine whether the health span and/or life span are similar to controls, or for twins relative to their noncarrier sibling. An assumption of no true cost, therefore, remains a hopeful one, but an assumption nevertheless. One relevant example that may temper optimism concerns work in fruit flies using the “Shaker” gene mutation that shortens sleep duration [ 11 ]. Evaluated longitudinally, the life span of these mutant flies was significantly shorter relative to wild-type flies. This would suggest that some short sleep gene variants, at least in certain species, may come with a consequence only when assessed longitudinally, in this instance, premature mortality.

Genes not only affect sleep, but the reverse is also true. During time spent awake, the double-stranded backbone of DNA accumulates breaks. This damage is specific to neurons compared with nonneural brain cells such as Schwan cells or peripheral endothelial cells [ 12 ]. However, during sleep, these double-strand breaks are repaired rapidly [ 13 ], suggesting that a lack of sleep can induce excessive mutations and potentially explain why sleep is so evolutionary conserved. These findings also support the view that sleep is especially critical for the brain with regard to the cellular function of neurons, although it is possible that neural cells in the periphery (e.g., in the enteric system) are similarly affected. Fascinatingly, the DNA damage response, in turn, can impact sleep: Expression of the DNA repair enzyme PARP1 can induce sleep [ 14 ].

The gut microbiome: A sleep interface?

Sleep, it was logically believed, primarily serves the sleeping organism itself. This view has changed, or at least been revised, in a model of symbiosis. Within us lives a diverse community of microorganisms, particularly in our gut, collectively known as the gut microbiota. The gut microbiota is composed of several billion bacteria, viruses, fungi, and additional microbes [ 15 , 16 ] and is known to influence a broad swathe of host physiology and behavior [ 17 ]. Dysfunction of the microbiome is now linked to numerous disorders and conditions, including obesity, type 2 diabetes, cardiometabolic diseases, nonalcoholic liver disease, and several immune disorders, as well as neurological disorders such as autism spectrum disorder, Alzheimer’s disease, depression, multiple sclerosis, Parkinson’s disease, and stroke [ 18 – 20 ]. Seminal work by Toth and Krueger [ 21 , 22 ] first linked sleep and the microbiota in the 1980s. Although, this field of research is still in its embryonic stages, a plethora of recent work is now providing exciting, and many surprising, new insights to add to those made by Toth and Krueger many decades ago. This is of particular interest as it could further promote the way we think about the established link between sleep and immunity [ 23 , 24 ], as the microbiome is fundamental for the development, training, and operation of the host’s immune system [ 25 , 26 ]. Most alluring, this relationship between the microbiota and sleep is bidirectional, opening up the possibility that modifying the gut microbiota may be a new tool for improving human sleep.

How sleep impacts the gut microbiota

Chronic sleep disruption alters the configuration of the gut microbiota in several deleterious ways. A pioneering study in mice investigated the effects of 4 weeks of repeated sleep interruptions. The mice were gently handled every 2 minutes to trigger awakening, mimicking the frequency of interruptions as a model of obstructive sleep apnea (Glossary) in humans [ 27 ]. After 9 days, the amount of Firmicutes bacteria in the gut, which are associated with the fermentation processes involved in energy extraction, increased. Conversely, Bacteroidetes species decreased, which is notable as they serve anti-inflammatory functions. As predicted, the mice had increased markers of inflammation and infection, including the number of macrophages and neutrophils. In tandem with these microbiota changes caused by a lack of sleep came an increase in food intake [ 27 ]. This resulted in escalating amounts of visceral fat, even though total body weight remained constant [ 27 , 28 ], suggesting an impact on how the body partitions energy when sleep loss alters the microbiome. Encouragingly, these changes subsided within 2 weeks of restoring healthy sleep.

Similar causal evidence in humans has since emerged, although with some inconsistencies. Two consecutive nights of sleep restriction (approximately 4 hours per night; Glossary) moderately increased the ratio of Firmicutes to Bacteroidetes in humans [ 29 ], similar to the results observed in the mice [ 27 ]. By contrast, in a study that looked at 1 week of similar 4-hour per night sleep restriction, the authors failed to detect a change in microbiota composition [ 30 ]. Increasing the severity of sleep restriction to 2 hours each night for 3 consecutive nights did, however, significantly reduce the diversity of microbiota in the gut, leading to dysbiosis (an imbalance in the microbial communities living in the gastrointestinal tract; Glossary). This was especially true for a decrease in Ruminococcaceae, which normally contributes to the production of short-chain fatty acids (e.g., butyrate) [ 31 ]. Short-chain fatty acids help improve gut outer barrier integrity and metabolism and regulate immune function and blood pressure [ 32 ]. Yet, the changes in the diversity of the microbiome were not accompanied by changes in gut permeability, at least when assessed using urine samples [ 31 ].

While most of society’s sleep debt is brought about by sleep restriction, there are circumstances in which total sleep deprivation is common and necessary, including in medicine, and for those working as emergency responders, in the military, in aviation, and in law enforcement. When individuals are acutely sleep-deprived for 40 hours [ 33 ], a dose-dependent escalation of gut dysbiosis unfolds, the severity of which increases the longer without sleep an individual goes. Replicating earlier studies in mice, the progressive dysbiosis is paralleled by increases in circulating inflammatory markers, including the pro-inflammatory cytokines IL-1, IL-6, and TNFα. In addition to securing sufficient sleep, new findings point to sleep regularity as an independent emerging factor in protecting gut health [ 34 ]. In experiments in rats, circadian rhythm disturbances triggered by an 8-hour circadian shift every 3 days can lead to imbalances in gut microbiota composition and rhythms [ 35 ]. In humans, greater objectively measured night-to-night variability in sleep duration, together with increased time awake after sleep onset and lower sleep efficiency, are associated with lower microbiome diversity [ 36 ]. Thus, irregular sleep patterns, especially if coupled with poor-quality sleep, interfere with stable profiles of gut microbiota, one consequence of which is poor metabolic health [ 37 ].

A clever study has added new insight into the link between dysbiosis and inflammation caused by insufficient sleep by using a combination of species [ 33 ]. If the microbiota of sleep-deprived humans is transplanted into well-rested, non-sleep-deprived mice, those mice experienced a significant increase in inflammation relative to mice who received a transplant from well-rested humans. In addition, these pro-inflammatory effects caused by lack of sleep extended into the brain, with levels of pro-inflammatory cytokines IL-1 and IL-6 increasing in the medial prefrontal cortex and dorsal hippocampus, while levels of the anti-inflammatory cytokine IL-10 decreased. These findings confirm at least one of the directions of effect, such that changes in the gut microbiota caused by a lack of sleep represent an explanatory path leading to systemic inflammation [ 33 ]. In addition to changes in circulating markers of inflammation, there was increased expression of Iba-1protein, an index of microglia activity (the brain’s primary immune cells) in the medial frontal cortex and hippocampus following transplantation. These findings suggest that the cognitive effects of sleep deprivation could, in part, be mediated by brain inflammation caused by the sleep-loss-induced changes in gut microbiota composition. It also provides a possible biological mechanism—changes in glial inflammatory activity—that might explain how and why chronic gut dysbiosis and brain disorders are related.

How the microbiota impacts sleep

Like so many other core physiological consequences, the idea that a lack of sleep impairs the microbiome is perhaps to be expected, but the idea that the microbiome could conversely impact sleep is more novel. The first pioneering investigation into this topic involved a 4-week antibiotic regimen in mice to deplete their gut microbiota [ 38 ]. Following the antibiotic course, the mice experienced a 100,000-fold reduction in gut bacteria. However, the causal manipulation of the microbiome led to a significant impairment in their brain’s ability to generate normative sleep in several ways. First, the mice aberrantly flip-flopped back and forth between NREM and REM sleep, indicative of unstable sleep-state regulation. The wake phase also suffered after the microbiome had been depleted. The mice could not sustain robust wakefulness across this period, experiencing excessive wake-time sleepiness. Added to this were uncharacteristic intrusions of NREM and REM sleep during the wake phase when the mice should otherwise be alert; the latter stage also pervaded into the sleep phase. Even the electrical brainwave quality of REM sleep was abnormally slowed in the microbiome-depleted mice. While preliminary, and despite the potential impact of antibiotics treatment on sleep patterns, these findings offer promising therapeutic potential. If microbiota composition can alter sleep, microbiome-specific interventions to restore and improve sleep may be possible.

The microbiota, sleep, and disease

Given that experimental sleep loss impairs the gut microbiota, disorders showing sleep disruption would be expected to show co-occurring impairments in the composition of the microbiota. Insomnia is one such confirmatory example. Both acute (lasting days to weeks) and chronic insomnia (lasting months to years) have now been linked to significant gut dysbiosis and a decrease in bacteria that produce short-chain fatty acids. Indeed, individuals with these conditions showed increases in circulating levels of the pro-inflammatory cytokine IL-1β, suggesting the increases in inflammatory response observed in sleep disruption in the lab are the everyday reality of individuals with insomnia [ 39 ]. Collectively, these cross-sectional observations reinforce experimental data indicating that disrupted sleep (Glossary) robustly compromises the gut microbiome.

Longitudinal studies tracking several hundred patients over a 6-year period have since found similar impairments. No matter whether patients were recently diagnosed with insomnia or had been experiencing insomnia for many months or years, all went on to show gut dysbiosis, relative to healthy individuals who slept well [ 31 , 40 ]. This included a reduction in Ruminococcaceae bacteria, notable for their varied functions, including regulating the gut barrier integrity that normally shields an organism from pathogens. Notably, patients who went on to recover from their insomnia ultimately became indistinguishable from healthy individuals in their microbiome composition.

Possible mechanisms

Since sleep impacts the microbiome, and the microbiome alters sleep, how do these distant systems converse? We would tender several candidates. First, a lack of sleep skews eating behavior, increasing food intake, biasing preference for higher caloric foods, and driving up consumption of simple and complex carbohydrates [ 41 ]. This altered eating behavior could, by itself, alter the gut microbiota by increasing the level of energy-extracting bacteria, which are responsible for digesting 10% to 30% of the nutrients that the digestive system cannot digest on its own [ 42 ]. Since the relationship among different species of bacteria is often competitive, this increase in energy-extracting bacteria occurs at the expense of bacteria that regulate other functions, such as combating inflammation [ 27 ]. These changes in microbiota may then lead to even greater sleep impairment, further slanting eating behavior, and instigating a vicious cycle [ 43 ].

A second direct pathway is the vagus nerve, which connects the brain to the gut’s intrinsic nervous system, called the enteric system. If rats have their vagus nerve severed, they are not affected by microbiome-related inflammation caused by sleep deprivation [ 44 ]. This indicates that the gut microbiome and sleep communicate, in part, in almost real time by way of the vagus nerve.

A third indirect pathway involves allostatic distress (Glossary). Sleep disruption increases the activity of the sympathetic nervous system and the hypothalamic adrenal pathway, increasing heart rate, decreasing heart rate variability, and increasing stress-related chemicals including catecholamines and cortisol [ 45 ]. Arousal-related catecholamines, primarily norepinephrine, and overactivation of the sympathetic nervous system can stimulate the growth of pathogenic bacteria such as Escherichia coli [ 46 ]. Aberrant sympathovagal drive, paired with catecholamines and glucocorticoids, may then change the microbiota habitat by increasing gut motility [ 47 ] and relevant iron availability [ 48 ].

Therapeutic implications

With the multitude of pathways on offer, if an unhealthy microbiome impairs sleep, it follows that improving microbiome health may represent a novel therapeutic tool for improving sleep. While no causal interventions yet exist in humans, a recent study in mice offers early clues. Mice received a 4-week treatment of Lactobacillus fermentum PS150, a “psychobiotic” bacterium strain previously shown to reduce stress in rats [ 49 ]. At the end of the 4-week supplementation with L . fermentum , the mice were placed into the standard anxiogenic challenge of a new environment that reliably triggers sleep disruption [ 50 ]. The control mice displayed the typical reduction in NREM sleep caused by the anxiogenic challenge. By contrast, the mice who received the microbiome supplementation showed sleep resilience, suffering no such sleep impairment. While not a direct demonstration, it nevertheless hints at a functional pathway wherein improving gut microbiota may improve sleep. If correct, it may usher in a new concept of “physiobiotics,” here facilitating the physiological process of sleep (i.e., somnobiotics), beyond the psychobiotic field.

Therapeutic enhancement of human sleep

Throughout most industrialized nations, almost 1 out of every 3 individuals sleeps less than the recommended 7 to 9 hours of sleep per night [ 51 , 52 ]. Current pharmacological sleep aids have limitations and adverse effects [ 53 ] and the number of qualified individuals available to provide the behavioral alternative treatment of cognitive behavioral therapy for insomnia (Glossary) is limited, relative to the demand [ 54 ]. Thus, a need exists for new approaches that are cost-effective, low friction (i.e., interventions requiring minimal user effort or resources), have high compliance, and are scalable at a societal level. Emerging research developments, including electrical and acoustic brain stimulation, kinesthetic methods, and thermal manipulations, are beginning to show promise ( Fig 2 ).

Several different noninvasive methods have been developed for artificially augmenting human sleep. (A) Electrical brain stimulation, including when it is time-locked to the upcoming peaks of individual deep NREM sleep brain waves, can enhance the power of those slow waves in a mechanism similar to the external assistance, or pushing, of a swing. ( B ) A similar outcome can also be achieved by slowly rocking a bed at frequencies close to the slowest oscillations of deep NREM sleep (purple, approximately 0.25 Hz), leading to an increase in the amount of deep sleep, and helping with a faster sleep onset, relative to a stationary bed (gray). ( C ) Thermal stimulation of specific regions of the body represents another method for artificially improving human sleep. Normally, the mechanism instigating human sleep (sleep onset) involves an increase in skin peripheral temperature of vascular regions such as the hands and feet (yellow dashed line). As the blood rises to the surface away from the inner body, core body temperature decreases, and the coincidence of these 2 changes provides a thermal signal triggering sleep onset (red dashed line, left-side panel). Thereafter, further decreasing core body temperature is associated with increasing amounts of deep NREM sleep. By artificially accelerating these transitions, mostly by experimentally warming the hands and feet, core body temperature decreases more rapidly, therefore reducing the time it takes those individuals to fall asleep (right-side panel), with further such thermal intervention subsequently increasing the amount of deep NREM sleep and reducing the amount of nighttime awakenings (i.e., increasing sleep stability and the consolidated nature of sleep).

https://doi.org/10.1371/journal.pbio.3002684.g002

Electrical sleep stimulation

Slow brain waves are the hallmark of deep NREM sleep and quickly became a natural candidate for approaches using noninvasive electrical brain stimulation. Early findings demonstrated that applying 1 Hz transcranial direct current stimulation during NREM sleep over the frontal lobe (a main epicenter of NREM SWA) can boost naturally occurring slow waves by up to 60% in healthy adults [ 55 ]. The sleep enhancement was meaningful, with individuals consolidating memories during this enhanced sleep in a superior manner, therefore forgetting less the next day [ 55 ]. A number of replication studies have since been published, though with some exceptions [ 56 ]. There has, however, been an unexpected change in sleep in the story of slow brainwave stimulation. In numerous electrical stimulation studies, the boost in SWA came with a secondary enhancement of sleep spindle activity, as was observed with kinesthetic rocking. This would indicate that, independent of the stimulation method (movement or electricity), when SWA is boosted, increases in faster-frequency bursts of sleep spindles also follow.

Although SWA has classically been linked to the enhancement of fact-based memory (i.e., textbook-like memory), so too have sleep spindles [ 57 ]. New closed-loop monitoring methods of electrical brain stimulation (i.e., a control system wherein the deviation signal of sleep is measured in real time and used to control the action of ongoing brain stimulation to fine-tune and perfect) have selectively targeted sleep-spindle frequencies [ 58 ]. Artificial sleep-spindle enhancements also led to superior next-day memory recall of previously learned facts [ 59 ], although interestingly, they did not improve motor-skill motor memories, which are also known to be improved by naturally occurring sleep spindles [ 58 ].

One of the most reliable and striking physiological changes as we age is a pernicious erosion of sleep, with a disproportionately large decline in deep NREM sleep [ 60 ]. This change is further exacerbated in those with dementia [ 61 ]. Considering the cognitive hallmark of aging linked to memory failure, and the fact that deep NREM sleep aids overnight memory consolidation, the direct health and disease applicability of electrical brain stimulation in older individuals and those with dementia has become a target. To date, electrical brain stimulation has, with some degree of consistency, improved the quantity and quality of deep NREM SWA in older adults, and those with dementia [ 62 – 64 ]. While large-scale randomized controlled trials are still required, transcranial stimulation is seen as promising since it is inexpensive and somewhat pragmatic and, therefore, scalable.

At least 2 applications have emerged. First is the use of electrical brain stimulation for facilitating healthy aging and potentially reducing the cognitive burden of dementia and/or enhancing glymphatic brain clearance of amyloid and tau proteins (see the section on “ To sleep, perchance to cleans the brain ”). Second, and lofty in speculation, is the question of whether such technology could offer a future in which we shift from a model of late-life treatment of aging and age-related disorders to a model of midlife prevention. It is during the fourth decade of human life that the decline in deep NREM sleep begins [ 65 ]. Starting a regimen of sleep augmentation at this time (e.g., as we commonly do with calcium supplementation to prevent osteoporosis) could help bend the arrow of age-related ill-health and dementia risk down on itself by maintaining life-long quality sleep.

Acoustic sleep stimulation

Electrical brain stimulation still requires some degree of proactive motivation from an individual (applying the device each night, charging it, etc.). However, an alternative, low-to-no friction method for sleep enhancement is acoustic stimulation. When sounds are played without respect to ongoing slow waves, SWA is increased but memory retention is not improved [ 66 ]. A more sophisticated auditory stimulation approach has since emerged. Slow waves are detected in real time, with specialized algorithms predicting the timing peak of the next slow wave. At this time, a short sound is delivered to arrive at the peak of the next slow wave. This timed acoustic stimulation approach enhanced the expression of slow waves for some seconds after, and upon awakening, participants’ memory was 2-fold better compared with the unstimulated sleep nights [ 67 ]. A recent meta-analysis [ 68 ] has confirmed reliable and moderate effect sizes of acoustic sleep stimulation and the associated memory benefits.

Kinesthetic sleep stimulation

In the human historical record, there is ample reference to rocking a small infant to invite sleep with alacrity. Several recent reports, in humans and nonhuman species, provide physiological data that support this long-known parental wisdom of kinesthetic sleep stimulation [ 69 ]. When healthy adults sleep on a bed suspended from the ceiling during a nap period, and the bed is then rocked laterally at an even, slow frequency of 0.25 Hz, sleep is enhanced [ 69 ]. Seeking to mimic the frequency of the very slowest NREM sleep slow waves, this 0.25 Hz stimulation had participants falling asleep significantly faster, spending less time in the shallowest stage of NREM sleep, entering a deeper stage of NREM sleep sooner, and obtaining more of that deeper sleep, relative to when they slept without the rocking motion. Deconstructing the sleeping brainwaves, the rocking method boosted the amount of ultraslow NREM sleep waves (0.5 to 1 Hz) and increased another physiological bursting oscillation often paired with these slow waves, called sleep spindles (10 to 15 Hz).

Recently, these findings were replicated across a whole night’s sleep [ 70 ], with the study further showing that these rocking-induced benefits also had functional effects. Participants performed almost 10% better on a memory test after sleeping on the rocking bed compared to when sleeping on the stationary bed (not dissimilar to a full grade increase on an exam). Similarly, mice that were rocked gently by having their cage placed on a moving platform fell asleep faster, and spent more time in NREM sleep, although without changes in brainwaves. Elegantly, when the same experiment was performed on mice lacking sensitivity to linear movement, they did not experience any changes in their sleep patterns, confirming that it is the kinesthetic movement that augmented the sleep benefit [ 71 ]. By employing a vibrating pad, set at a specific frequency, even fruit flies can be lured into slumber [ 72 ]. Interestingly, with each repetition of the rocking procedure, the flies fell asleep more rapidly. However, this enhancement occurred only when the frequency remained unchanged; any slight alteration prompted the flies to reacquaint themselves with the new rhythm.

These latter findings suggest that the process of getting used to sensory stimulation helps in reducing arousal levels and, thus, promoting sleep [ 72 ]. More generally, the idea that a slow rocking kinesthetic improves sleep has already spurred the development of at least 1 commercial appliance at the time of writing this article. The device—essentially a set of 4 sturdy motor-driven movement pads—is placed under the feet of the bed. The pads instigate a rocking motion at the aforementioned slow frequency with the hope of sleep improvement (Enseven LLC, Arizona, United States of America).

Thermal sleep stimulation

If you isolate an individual from time and context cues, they will unwittingly report the greatest natural urge to sleep precisely when their core body temperature begins to plummet [ 73 ]. Temperature, therefore, offers 1 novel and newly harnessed pathway for enhancing human sleep [ 74 , 75 ]. The main evidence for this comes from pioneering work carried out by a team of sleep scientists led by Eus van Someren [ 76 ]. The team ingeniously developed a thermal bodysuit filled with tubes, much like veins, capable of selectively perfusing water of different temperatures to any specific part of the body. To artificially accelerate a drop in core body temperature, the scientists first focused on increasing the temperature of the peripheral extremities (hands, feet, arms, legs). When these peripheral areas are warmed, blood rises to the skin’s surface. As a result, warm blood from the inner core of the body is encouraged outward, allowing the rapid expulsion of core body heat, dropping central body temperature, and thereby inducing sleep. By controlling the temperature of the perfused water, they effectively accelerated the natural temperature drop that facilitates sleep (i.e., peripheral body warming to cause core body cooling; Fig 2 ). As a result, they had participants falling asleep approximately 25% faster than was normal for them. As they continued to mimic the body’s natural thermal sleep change further into the night, more sleep benefits unfolded. By continuing to cool the body into the first half of the night using the same suit, the scientists reduced the amount of time awake, thus increasing the amount of time spent in stable sleep, and the electrical quality of deep NREM sleep also increased [ 76 ].

Elderly individuals are one population that struggles with sleep and thermoregulation. Van Someren and colleagues have since targeted these older adult populations [ 77 ]. Before the body-cooling therapy, older adults in the study had more than a 50% probability of waking up in the last half of the night. After applying the thermal cooling manipulation throughout the night, the number decreased to less than 5% likelihood, and deep NREM sleep also increased.

Of course, thermal suits are not scalable owing to high cost and low compliance. However, baths and showers are a simpler, cheaper, and accessible alternative. Upon exiting the warm bath or shower, heat is again expelled faster and more efficiently from the body than without either of these thermal manipulations, leading to a drop in core body temperature [ 78 ]. A collection of studies utilizing warm baths or showers before bed [ 78 – 81 ] have, on average, resulted in individuals falling asleep between 10% and 30% faster, having fewer awakenings at night, and increasing the amount of NREM sleep by 50 additional minutes, relative to nights without prior hot bath or shower interventions. There may be a cost though. Some studies have reported a co-occurring decrease in REM sleep following hot baths or showers, either due to the NREM increase or to a change in body temperature shifting away from that which is optimal for REM sleep. Notably, manipulating REM sleep using temperature has been achieved by changing the ambient temperature in the room of the sleeper, rather than skin temperature. Absent sheet bedding, when the ambient temperature is close to thermal neutrality for endotherms (which, for humans, is between 29°C and 31°C, or 84°F and 88°F), REM sleep is maximal [ 82 , 83 ]. In rodents, when the ambient temperature is increased from 22°C to 29°C, moving more toward the thermal neutral zone, REM sleep more than doubles [ 84 , 85 ]. Nevertheless, the effect follows an inverted U-shape function, with REM sleep decreasing back down if the temperature is increased to 36°C [ 84 , 85 ]. Consumer technology groups have taken note. Smart home thermostats for ambient room temperature, and thermal-modulating mattresses controlling the temperature below the covers, all offer scalable approaches to altering human body temperature during sleep, although no formal peer-reviewed articles have been published to date.

Novel pharmacological sleep aid

Another development for enhancing REM sleep has emerged from the pharmacological arena. Over the past decade, drugs targeting receptors for orexin (also known as hypocretin) have emerged. Orexin is a neuropeptide that stimulates wakefulness and food intake [ 86 , 87 ]. These drugs, known as dual orexin receptor antagonists (DORAs), block both orexin receptors (OX1 and OX2), thereby inhibiting wakefulness and promoting sleep. Unlike previously developed hypnotic drugs, such as benzodiazepines and Z-drugs, which predominantly augment NREM sleep in a sedative-hypnotic manner, DORAs promote a different sleep signature. The 3 dominant DORAs (suveraxant, lemborexant, and daridorexant) not only enhance sleep by reducing sleep onset latency, wakefulness after sleep onset, and total sleep time [ 88 ], but these medications also reduce the time to the first appearance of REM sleep and increase the total amount of time spent in REM (suverxant [ 89 ], lemborexant [ 90 ], Deoraxant: N/A). Surprisingly, only 1 study (looking at suverxant) has published electroencephalogram (EEG) spectral data that offers insight into the effect of the drugs on sleep oscillations [ 91 ]. No significant changes to electrical EEG activity in REM or NREM sleep were observed at any of the wide-ranging doses of the drug used (even after 28 days of use). While preliminary, such data suggest that the DORAs consolidate and lengthen sleep without altering its fundamental oscillatory characteristics of cortical activity. Notably, when administered to older adults with suspected Alzheimer’s disease, suverxant increased sleep duration by 73 minutes per night (28 minutes more than placebo) [ 92 ]. In addition, recent findings in a small group of unimpaired middle-aged adults indicated that suverxant use decreased amyloid-β levels overnight by 10% to 20% in the cerebrospinal fluid (CSF) [ 93 ], the consequences of which we discuss in the next section.

To sleep, perchance, to cleanse the brain?

The body’s cleansing system, or lymphatic system, was first described in the 17th century by Olaus Rudbeck and Thomas Bartholin [ 94 ], yet the existence of any such cleansing system within the brain was not discovered until 1984, when Patricia Grady and Marshall L Rennals replaced the CSF of anesthetized cats and dogs with a tracer solution that could be tracked in brain slices under the microscope [ 95 ]. Still, it was only in 2013 that a team of researchers led by Maiken Nedergaard published a landmark set of discoveries that associated this cleansing system with sleep and postulated that it may explain why animals (or metazoans) with nervous systems require sleep.

The glymphatic system of the brain is made up of a matrix of glial cells that are nonneuronal in nature and utilize a set of water channels called aquaporins on their end feet [ 96 ]. Glial cells combine to form a space around the brain’s vasculature, called the perivascular space, in which CSF flows [ 97 – 100 ]. The glymphatic system services the removal of metabolic detritus, solutes, and toxins from the brain, specifically from the interstitial space between neural cells [ 98 ].

Sleep and the glymphatic system

Nedergaard and colleagues’ discovery, together with the contributions of many others [ 96 , 101 ], has established that the pulsing, cleansing glymphatic mechanism is not always switched on in high-flow volume across the 24-hour period. Instead, it is during sleep, and particularly during NREM sleep, that the glymphatic system shifts into full tempo. A seminal study in mice utilized CSF tracers to measure the CSF pulsing flux throughout the brain. When the mice were awake, CSF flow was minimal; however, when the mice entered NREM sleep, CSF flow increased considerably [ 97 ]. Strikingly, the extracellular space between the brain’s cells and structures (interstitial space) increased by 60%. As a result, there was markedly greater CSF flow coursing through the interstitial space, enhancing the exchange of waste products between the CSF and brain cells. Two notable waste products removed are amyloid-β and tau proteins, the excess accumulation of which is the hallmark of Alzheimer’s disease, and which we will return to in the section on “Disease implications” [ 102 ].

In humans, various studies have demonstrated that sleep has a causal role in removing waste products from the brain. Depriving individuals of sleep for an entire night, or even just selectively reducing the amount of deep NREM sleep (while holding a constant total sleep time), results in a next-day increase in amyloid-β and tau. This has been measured by markers in the circulating bloodstream [ 103 ], within the CSF (assessed using lumbar puncture) [ 104 ], and directly in the brain using amyloid-β- and tau-sensitive PET scans [ 105 ].

Sleep-dependent mechanism

Why is the sleep state essential for glymphatic clearance? First, the high levels of brain noradrenaline that dominate during arousal drop during sleep. Within the brain, one structural consequence is that the interstitial space expands [ 97 ], allowing for better-flowing conditions. Second, cardiorespiratory oscillations change markedly during NREM sleep. Both cardiac and respiration cycles slow down, respiration becomes deeper, and the temporal coupling between the two increases [ 106 ]. These pulses drive the mechanical contraction and dilation of the blood vessels, which, in turn, results in a corresponding and respective expansion and shrinkage of the space surrounding the vessels in which CSF resides [ 100 ]. Indeed, these cleansing fluctuations are 2 to 5 times larger in NREM sleep relative to the waking state [ 107 ]. Third, recent studies show that neural activity itself might influence CSF flow locally [ 108 ]. When neural activity decreases, the demand for fresh oxygenated blood decreases as well, which translates to narrower surrounding blood vessels and wider perivascular spaces that fill with CSF [ 108 ]. During NREM sleep, brain activity shows synchronous rhythmic SWA spanning vast brain areas, as opposed to the faster and desynchronized brain activity observed during wakefulness. The newly discovered involvement of brain activity affecting CSF flow could explain how spatially coordinated and rhythmic neural activity during NREM sleep, as opposed to the erratic and spatially diverse metabolic demands during wakefulness, supports efficient cleansing by synchronously widening the vascular space across larger brain territories.

The majority of mechanistic data illustrating the sleep-dependent operation of the glymphatic system has been in mouse models. However, a recent seminal study in humans employing a novel functional MRI (fMRI) marker to measure the strength of the CSF flow signal has provided the first hints of the same mechanistic system at work. As participants went into NREM sleep inside the MRI scanner, a significant increase in CSF flow was observed at the fourth ventricle, a large CSF cavern deep in the brain. Interestingly, this surge in CSF flow was preceded by a coupled increase in whole-brain oxygenated cerebral blood flow, which was, in turn, preceded by the electrical SWA that is prevalent in NREM sleep [ 109 ]. Thus, a physiomechanical rhythm creates a corresponding pulse and flow of CSF fluid, thereby representing a sleep-dependent pathway that supports the glymphatic sanitary service.

Disease implications

Impaired glymphatic clearance has been described and/or proposed in a collection of neurological disorders, including Alzheimer’s disease, traumatic brain injury, and Parkinson’s disease, as well as in psychiatric disorders [ 110 ]. Of note, every one of these conditions has well-established impairments in sleep. Of these, the most studied is the relationship between impaired sleep, Alzheimer’s disease, and the glymphatic system [ 89 ].

Hour-to-hour fluctuations in amyloid-β levels across the 24-hour period correlate strongly with the sleep–wake cycle in both mice and humans, rising during the wake phase when sleep is absent, and declining during the sleep phase when sleep occurs. However, mouse models of Alzheimer’s disease, in which sleep is impaired, do not show such diurnal fluctuations [ 111 ], suggesting that appropriate waste clearance is not taking place due to deficient sleep. Relatedly, mice whose sleep is pharmacologically suppressed for 9 hours experience a 2-fold increase in tau levels [ 112 ] and a 17% increase in amyloid-β levels within the brain [ 111 ]. In humans, the lower average duration of sleep across the life span, together with the disorders of sleep apnea and insomnia, are all associated with increased amyloid-β levels in later life and/or with a higher risk of developing early cognitive decline and Alzheimer’s disease. Moreover, there is a progressive linear impairment of fMRI-measured CSF flow—a proxy for aspects of glymphatic activity—in later life, with the severity of impairment increasing with the transition in older adults from health, to those showing signs of mild cognitive impairment, and, finally, to those with Alzheimer’s disease [ 113 ]. Showing bidirectionality, treating sleep apnea in midlife delays the onset of cognitive decline by over a decade [ 60 , 114 ].

While these data offer an explanatory mechanism for the well-known link between insufficient sleep and Alzheimer’s disease, they also raise the question of sleep as therapy. If the decline in deep NREM sleep, which begins as early as the fourth decade of human life [ 65 ], can be prevented, one could conceivably be able to decrease Alzheimer’s disease risk.

Sleep and emotional health

Any parent knows that poor sleep in a child the night before leads to poor emotional reactivity the following day. The same, it turns out, holds true for adults. Insufficient sleep quantity, quality, and select NREM and REM sleep abnormalities are associated with emotional dysregulation, anxiety, aggression, and worse mood (effect-size range g = 0.39 to 0.94) [ 115 – 118 ]. Recent neuroimaging studies have further revealed a unique neural mechanism accounting for these alterations in mental health caused by a lack of sleep [ 119 – 121 ]. Most intriguing, the sleep manipulations used to produce these affective changes in healthy adults mimic those expressed in specific psychiatric and neurodevelopmental disorders, including major and bipolar depression, anxiety, schizophrenia, autism spectrum disorder (ASD), and attention deficit hyperactivity disorder (ADHD) [ 122 – 126 ]. Indeed, no major psychiatric disorder has been studied to date in which sleep is normal [ 124 ].

Sleep loss and emotional health

Three key domains of affective brain function become compromised when sleep becomes short or of poor quality: mood and emotional baseline; (mis)perception of other people’s emotions; and an individual’s outward emotional expressivity to other people.

Concerning the basic tenor of an individual’s emotional baseline, complete or partial sleep restriction worsens mood states and increases emotional reactivity. Consequently, negative feelings of anxiety, agitation, hostility, anger, and restlessness [ 116 , 117 , 127 , 128 ] and, to a lesser degree, impulsivity [ 129 – 131 ], are increased. However, the adverse effect of a lack of sleep on blunting positive emotions is even greater than that of amplifying negative mood. Almost all dimensions of positive mental health diminish with insufficient sleep, including feelings of happiness, excitement, energy, motivation, and the general ability to gain pleasure from normally pleasurable experiences (anhedonia) [ 115 , 117 , 132 , 133 ]. Sufficient research enabled 2 very recent meta-analyses to be performed that quantify how sleep compromises mental health. A large effect size was found for the blunting of positive affect by sleep loss (g = −0.94, n = 25 studies), while increases in negative mood and increases in anxiety were also robust, although less pronounced (g = 0.45, n = 55 studies; and g = 0.39, n = 34 studies, respectively [ 115 , 116 ]). Interestingly, recent data indicate an important role of sleep regularity in protecting better mood and emotional health [ 134 ]. For example, increased variability of sleep duration (as measured across a week) predicts lower satisfaction with life, greater depressive symptoms, and increased anxiety [ 135 ]. Similarly, variability in sleep timing from day to day precedes poor mood, and worsening mood the following week, and does so independently of age, sex, level of physical activity, and sleep duration [ 136 ]. These findings collectively support the realization that, in addition to sleep duration and quality, the consistency of sleep can also be linked to numerous mental health outcomes.

Beyond dulling pleasure while increasing states of negativity, sleep loss also impacts the intensity with which these emotions are experienced [ 137 ]. When facing a modest cognitive challenge (such as counting backward in steps of 2), sleep-deprived participants will rate it as more stressful than those who had a night of sleep [ 132 ]. This suggests that sleep loss changes the internal cutoff or emotional threshold the brain uses to determine our transition into emotional distress. As a result, sleep restriction, poor sleep quality, and irregular sleep have all been linked to heightened subjective stress [ 137 – 139 ], an association that is only exaggerated in children with ADHD or ASD [ 140 ]. Notably, sensitivity to stress is known as the “lowest common denominator” that promotes vulnerability, or exacerbates symptoms of almost all mental illnesses, the majority of which include sleep loss or insomnia as part of their diagnostic criteria [ 141 – 143 ].

The underlying mechanisms explaining these changes in our innate emotional balance have been linked to aberrative physiological changes to the brain and body. Within the brain, sleep loss increases limbic reactivity and decreases functional connectivity (Glossary) between the medial prefrontal cortex and limbic structures, thereby diminishing emotion regulation capabilities ( Fig 3A ) [ 133 , 144 – 147 ]. Notably, the neural circuit connecting the amygdala to the anterior cingulate cortex has recently been shown to protect against mood disruption triggered by one night of sleep deprivation in both healthy individuals and those with depression [ 145 ]. Such findings indicate that changes to amygdala connectivity following a lack of sleep have a significant role in shaping both emotion and mood regulation without sleep. These changes in connectivity can be viewed more generally as confirmatory to the synaptic homeostasis hypothesis [ 148 ], suggesting that one function of sleep may be to rebalance or downscale synaptic strength that is potentiated during the day.

(A) Within an individual, sleep loss (pink) triggers a sharp reduction in positive mood and, to a lesser extent, an increase in negative mood (left-side panel). The emotional intensity felt by sleep-deprived individuals is also amplified by lack of sleep. However, there is a paradoxical decrease in the outward emotional expressivity triggered by sleep deprivation (right-side panel). These affective changes are further reflected in the brain. Here, sleep loss increases activity in the limbic network involved in emotional processing (red, left-side brain) yet reduces activity in the mPFC (blue, right-side brain). In addition, functional connectivity between the mPFC and amygdala is also reduced by sleep loss (dashed blue line), which is a communication pathway that normally regulates emotion. ( B ) Interindividual affective processes and behaviors are also altered by sleep loss. For example, sleep loss increases feelings of loneliness within the sleep-deprived individual and lowers feelings of empathy towards others (left panel). This asocial phenotype within an individual is further reflected in the reduced desire to interact with other, rested individuals. This effect is bidirectional. Rested individuals, unknowing of the sleep-deprived state of their conspecific, nevertheless show a similar reduction in the desire to interact with underslept others (right panel). ( C ) Across larger societal scales, insufficient sleep impairs prosocial behavior observed in large groups of individuals. For example, underslept groups express a reduced overall trend of helping behaviors and reduced motivation of typical societal civic duties, such as volunteering or voting (left panel). One underlying mechanism accounting for these collective asocial consequences is impaired activity in the social cognition brain network of underslept individuals (right panel), which is relevant as this network normally supports the ability to understand the state of others (i.e., theory of mind), and also promotes prosocial helping and cooperation. ACC, anterior cingulate cortex; mPFC, medial prefrontal cortex; TPJ, temporal parietal junction.

https://doi.org/10.1371/journal.pbio.3002684.g003

Potentially related to the aforementioned changes in limbic brain connectivity, or contributing to them, are increases in autonomic pupillary reactivity, increased skin conductance, up-regulated cortisol release, and increased blood pressure following lack of sleep [ 149 – 154 ]. Such a collection of changes suggests an explanatory biological framework of skewed brain–body sympathetic drive in response to emotionally inciting events, although, paradoxically, when quiescent, a new study has shown an opposite pendulum swing to excess parasympathetic drive under sleep-loss conditions [ 155 ]. Similarly, habitual short sleep (<7 hours) has recently been linked with reduced amygdala reactivity compared to normal sleep duration (7 to 9 hours), potentially indicating long-term desensitization of limbic reactivity following chronic insufficient sleep [ 156 ].

In addition to internal emotional feelings, contemporary work has established that emotional perception becomes skewed when sleep is insufficient. As a result, individuals can perceive a distorted view of incoming emotional signals from others and from the world.

Following reductions in either sleep quantity or quality, participants pay greater attention to and react faster to negative emotional stimuli (relative to neutral or positive stimuli) [ 129 , 157 – 159 ]. More than a change in the rose tint of an individual’s emotional perception is the recent discovery of emotional misperception. Here, sleep-deprived individuals fail to discriminate accurately between the different gradings of emotional facial expressions [ 160 , 161 ], with sleep loss biasing individuals to perceive greater threat signals relative to safety [ 162 ]; i.e., sleep-deprived individuals will more commonly mistake friend for foe [ 163 ], consistent with the proposal that the underslept brain loses the appropriate “tuning curve” of accurate emotional stimulus discrimination [ 45 ]. Nevertheless, when using short clips of individuals enacting varied emotional expressions, rather than still images, sleep loss does not significantly impair emotion recognition [ 164 ]. One explanation for this is that richer, more dynamic stimuli might sufficiently heighten attentional focus, motivation, or levels of arousal to compensate for the otherwise observed discrimination impairments triggered by lack of sleep.

The third domain of emotional function altered by a lack of sleep is one uncovered only recently, perhaps in part because it was so paradoxical. Contrary to the prediction one would make based on the internal sensation of amplified negative emotions, combined with the physiological sympathetic and limbic reactivity, the outward emotional expressiveness of underslept individuals is stunted ( Fig 3A ). This has been demonstrated across the emotive level of vocal expressiveness and facial expressivity [ 165 – 169 ]; e.g., sleep loss reduces pitch variations when individuals speak, making their voice sound more monotonic or “flattened” [ 165 , 166 ]. Therefore, sleep-deprived individuals experience increased emotional sensitivity themselves yet suffer a paradoxical outward reduction in expressivity (of that amplified emotional state).

There are many implications for these discoveries. One of the most powerful ways that human beings communicate nonverbally is through emotional behavioral expressions (e.g., voice, face, movement) [ 170 ]. Consider a sleep-deprived patient in a hospital not being fully communicative of their pain state and, thus, not being given appropriate pain treatment by medical staff (particularly relevant as sleep-deprived individuals feel noxious stimuli as more painful relative to when they are well rested [ 171 – 173 ]). Indeed, this very absence of signaled outward expression may explain why sleep-deprived participants are routinely viewed as less desirable to interact with, propagating the impact of sleep loss into the social domain (as we discuss below).

Benefits of sleep for emotional health

Sleep loss and sleep restriction lead to clear detrimental effects on our emotional well-being. The latest work has inverted the question: What is it about sleep, when we do get it, that beneficially improves mental health? Initial findings highlighted the role of REM sleep in the support of emotional processes [ 174 – 177 ] and in providing a form of overnight therapy, dissipating the subjective intensity of emotion when individuals are reexposed to an emotionally challenging event from the previous day [ 178 , 179 ].

However, the most recent findings have offered a revision of this REM sleep focus, establishing a role of NREM SWA in offering complementary effects on the mood state of anxiety, more than moment-to-moment emotional reactivity. More specifically, the amount of time spent in deep NREM sleep, as well as the electrical brainwave quality of that deep sleep indexed in SWA, service an overnight amelioration of anxiety in healthy adults, returning it to baseline levels. The greater the amount and quality of NREM SWA, the less anxious the individual felt the next day. When sleep was absent, however, anxiety progressively increased across the night and into the next day [ 128 ]. Interestingly, the underlying neural mechanism associated with this deep-sleep anxiolytic effect was somewhat similar to the effects of REM sleep. Both the amount and the quality of SWA predicted the extent of medial prefrontal cortex reengagement the next day, a region essential for the down-regulation of anxiety, and which is impaired in those with anxiety disorders (who also have co-occurring deficiencies in NREM sleep) [ 180 – 182 ]. Sleep, and the unique biological states of REM and deep NREM, may therefore explain the prophetic wisdom of American entrepreneur, Joseph E Cossman, who once declared, “The best bridge between despair and hope is a good night’s sleep.”

Sleep-dependent prosocial control?

Humans are a social species, psychologically and biologically requiring social connectedness. Collectively, as a species, survival necessitates such social, interindividual cooperation [ 183 ]. Indeed, without prosocial cooperation and helping, the advent of modern societies would not have occurred.

Sleep is a fundamental prosocial glue that binds human beings and entire societies together. The impact of sleep, and a lack thereof, has now been elicited from the level of a single individual’s social proclivity (e.g., social approach, social withdrawal, and loneliness) through to the prosocial interactions between humans (including the complicated processes of empathetic understanding and cooperative helping), and all the way up to the en masse coordination of societal behaviors ( Fig 3 ).

Sleep loss and the (a)social individual

Within an individual, a lack of sleep leads to feelings of social disconnection and loneliness. Insufficient sleep, including that caused by insomnia, poor sleep quality, difficulty falling asleep, and greater daytime sleepiness, are all associated with greater loneliness and a reduced desire to interact with others [ 184 – 187 ]. Moreover, sleep loss changes the way individuals evaluate their own social experiences, reducing a sense of connectedness and related positive affect and reducing the desire to interact further [ 188 ]. In longitudinal studies, initial poor sleep quality (including sleep fragmentation) and lower sleep satisfaction are predictive of higher levels of loneliness 2 to 7 years later [ 189 , 190 ], while preexisting loneliness is predictive of worsened subjective sleep quality, highlighting the bidirectional link between sleep and social isolation [ 186 ].

By contrast, superior sleep quality, including an ability to fall asleep more quickly with fewer nighttime awakenings, is associated with a higher likelihood of daytime active socializing [ 191 ]. This relationship is especially true regarding prior NREM slow wave sleep (SWS), with greater amounts and quality of SWS resulting in increased amounts of real-world social interactions the following day [ 192 ]. Offering bidirectional evidence once again, the social isolation of mice triggered a significant decrease in sleep amount, most notably reductions in the electrical quality of deep NREM sleep [ 193 , 194 ]. Thus, insufficient sleep, specifically reduced amount and electrical quality of NREM, can lead to a behavioral phenotype of social withdrawal and loneliness, while loneliness and social isolation instigate impairments in sleep quantity and NREM quality—a self-perpetuating cycle. Yet, REM sleep also appears highly relevant. Recent work has established a causal role for REM sleep in the consolidation of social memory [ 195 ], such that REM-specific suppression of hippocampal neural circuits in sleeping mice lowered the typical preference for novel social interaction the next day [ 196 ]. Similar impairments in social novelty preference were also recently observed following sleep disruption in adolescent mice, an effect that was linked to impaired reward-related dopaminergic activity when meeting a new conspecific [ 197 ]. Together, such findings indicate that sleep disruption of numerous kinds and stages leads to a phenotype of social withdrawal and disengagement driven by sleep-dependent neural circuits that otherwise sustain adaptive prosocial behavior.

Sleep and interpersonal social interaction

In addition to changes within an individual, interactions between individuals are also dependent on sleep ( Fig 3B ) [ 119 , 198 , 199 ]. Among romantic partners, poor sleep quality is associated with greater conflict the following day, higher levels of aggression, and lower marital satisfaction [ 200 , 201 ]. In children and teens, poor sleep quality predicts increased hyperactivity, more conduct problems, more disagreements with peers, more violent behavior, and a greater propensity for bullying [ 202 – 204 ]. Similar outcomes are observed in children with ASD, in whom short sleep duration and poor sleep quality are also related to difficulties in social interactions and fewer prosocial behaviors [ 205 , 206 ]. Notably, improving sleep in individuals with ASD can alleviate their symptoms, increase social communication skills, improve appropriate emotional reactivity, and decrease maladaptive and repetitive behaviors [ 207 ].

Further leading to the interindividual erosion of social bonds by a lack of sleep, underslept individuals are rated as less interesting or desirable to interact with by well-rested individuals, even when those well-rested individuals know nothing about the sleep status of the people they are rating [ 208 , 209 ]. Sleep-deprived individuals are further rated as lonelier, less attractive, less charismatic, more anxious, and more unhealthy-looking by independent judges who are similarly blind to the sleep status of those individuals they are rating [ 184 , 210 ]. This suggests that sleep deprivation curates a form of individuals who are socially repulsing (in the literal sense of the word) to the rest of society.

Our workplaces also suffer the deleterious impact of sleep loss on social functioning. A lack of sleep decreases the extent of helping behavior among colleagues in the workplace [ 211 , 212 ] and raises levels of overall hostility between employees. Morality suffers, too. Underslept employees show a significantly higher probability of unethical behaviors, such as blaming someone else for their own mistakes, or dishonestly taking credit for someone else’s work [ 213 ]. The social disconnection between individuals that ensues from a lack of sleep has also been identified within the hospital setting, to ill effect. Doctors who have insufficiently slept when working a night shift are significantly less empathetic to their patients’ pain and, as a result of this deficient empathy, prescribe fewer analgesic medicines to help alleviate patients’ pain, relative to doctors working a day shift [ 214 ].

A new development has added a peculiar feature to our understanding of sleep’s influence on interindividual dynamics. When a well-rested individual interacts with an underslept individual, the nonverbal signals of loneliness emitted by the sleep-deprived participant can be “transmitted” to the well-rested individual, making the well-rested person feel lonelier themselves [ 184 ]. Such virus-like propagation from sleep-deprived to well-rested conspecifics intimates that the ill effects of sleep loss can spread to nearby social circles and further aggravate loneliness, leading to a wider-reaching impact of insufficient sleep on social withdrawal.

Sleep and society

Moving beyond interpersonal interactions, new developments point to an influence of sleep loss in altering the unique societal forces that shape human communities. Humans help each other—helping is a fundamental aspect of social humanity and one that is eroded by a lack of sleep [ 215 ]. For example, decreasing sleep simply by 1 hour diminishes helping acts of civic engagement, such as signing petitions and volunteering [ 216 ], and reduces the likelihood of voting across multiple different nations [ 216 , 217 ]. Insufficient sleep, be it total deprivation or simply modest night-to-night fluctuations in sleep quality, also leads individuals to withdraw their normal proclivity to help others [ 215 ] ( Fig 3C ). One study examined over 3 million charitable donations made in the USA in the past decade. The loss of 1 hour of sleep opportunity, using the manipulation of the change to Daylight Saving Time, substantially decreased altruistic helping across all states that undergo a clock transition [ 215 ]. This same dent in compassionate gift-giving was not seen in regions of the country that did not change their clocks and, thus, whose sleep was uncompromised.

How a lack of sleep produces this potent impact on human sociability appears to be driven, in part, by alterations in brain networks that compute and make complex social choices. The social cognition network, which involves regions of the medial prefrontal cortex, mid and superior temporal sulcus, temporal–parietal junction, and the precuneus [ 218 – 220 ], helps support social computation and, consequently, decisions on appropriate prosocial actions [ 221 – 223 ]. Two recent studies have shown that a lack of sleep impairs the activity and social responsivity of this network [ 184 , 215 ]. Furthermore, the magnitude of impairment predicted a greater withdrawal of choices to help others [ 215 ], suggesting a neural basis for asociality when sleep gets short. Such an effect of sleep on the higher-order complex social computations of the brain remains even when taking into account changes in negative mood and motivation. Moreover, sleep loss could stunt the altruistic helping nature of the individuals in a manner that discounted close social bonds, such that participants who had had insufficient sleep withdrew their help to others regardless of whether those in need were strangers or people they personally knew, such as close friends or family members. These results suggest that sleep loss can trigger a phenotype of asocial behavior with a broad and indiscriminate impact.

Parenthetically, data have indicated a steady decline in empathy behavior and civic participation in the USA over several recent decades [ 224 , 225 ] that is paralleled by declines in sleep quality and aspects of sleep quantity across the same time period [ 226 , 227 ]. Reductions in sleep quantity and quality in industrialized nations may thus be a previously unconsidered factor contributing to some asocial trends.

What is in a dream?

Each night, individuals experience a state of altered consciousness known as dreaming. At times, they are notably disorientated, losing track of time, place, and person. They experience hallucinations, perceiving things that are not present, and show signs of being delusional, believing things that are clearly not possible. Added to this are large emotional pendulum swings, vacillating between extreme positive and intense negative emotions. Finally, upon awakening, they endure a degree of amnesia, forgetting large segments of the bizarre journey that has just happened, if not the entire experience. If this was not peculiar enough, almost all of this experience unfolds without any volitional control. This is the state of dreaming, and since the record of human species began, dreams have been a noted part of it [ 228 ]. However, only recently have sleep scientists begun to understand some fundamental aspects of dreaming, including how human brains dream and if other species show similar neural instantiation of the dream state; what, if any, function(s) dreams serve (above and beyond the state of sleep they come from), leading to the development of dream therapies to restore these benefits; how to “mind read” the dreams of others using fMRI; and if and how individuals volitionally control their dreams (known as lucid dreaming).

How the brain dreams

Depending on the definition, dreaming occurs in almost every sleep stage. However, prototypical dreams—those that most people would label as such—principally occur during REM sleep. As a result, neuroimaging studies were initially focused on REM sleep to uncover the objective neural underpinnings that explain dreaming [ 229 – 234 ]. A canonical signature emerged ( Fig 4A ). First, both primary and higher-order visual regions became strongly active as the brain entered REM sleep, aligning with the vivid visual nature of dreams. Second, areas involved in motor functions such as motor and premotor cortices, the cerebellum, and the basal ganglia also became activated, consistent with the perception of first-person actioned movements. Third, limbic brain areas responsible for emotional processing, including the amygdala, hippocampal formation, and anterior cingulate cortices, display heightened activity, potentially accounting for the intense emotional tone dreams commonly take [ 235 – 237 ]. More interesting, however, were large regions of the brain that showed a converse decrease in activity during this otherwise highly active brain state of REM sleep, including the prefrontal cortex, the functions of which include volitional control and deliberative decision-making. Without knowing the experience of the individual, or even their state, should one look at this stereotypical pattern of brain activity and predict what subjective experience the individual was having, it would be a reasonable description of dreaming: perception of visual elements, motor action, emotionally laden, layered with autobiographical memories, yet disorganized, illogical, and without volitional control.

(A) Brain activation during REM sleep—one of the principal stages associated with vivid dreaming. Relative to brain activity when an individual is either awake or in non-REM sleep, there is increased activation of visual, sensorimotor, and affective pathways during REM sleep (golden clusters). Additional regions then come online and are activated when individuals experience lucid REM sleep (red clusters; relative to nonlucid REM sleep). These include regions of the anterior prefrontal cortex involved in volitional executive decisions and actions, and the precuneus, involved in self-referential processing. ( B ) Incorporation of recent waking events into dreams unfolds in a 2-peak reliable pattern over time. The first temporal peak of waking incorporations occurs on the first 2 nights and then fades. However, these same prior waking experiences reemerge as a second peak 5–7 days later. This temporal pattern of waking life incorporation is known as the dream lag effect. ( C ) IRT is a behavioral intervention method for treating and dissipating nightmares. IRT includes the waking rehearsal of alternatives to nightmare scenarios, developed between the patient and their therapist. These more neutral or positive alternatives to the nightmare scenario are rehearsed daily by the patient for up to 2 weeks. As a result, the nightmares become significantly less distressing. A recent study added an additional methodological step. During the daytime rehearsal of the nightmare alternative, an auditory tone (here, a piano chord) was played every 10 seconds in the background. Then, as the patient slept and went into REM sleep—the stage most commonly associated with nightmares—the same piano chord was played at a level that did not wake the patient up. The goal was to reactivate the memory of the alternative scenario as the sleeping brain is processing. As a result, patients experienced an even larger decrease in the distressing nature of the nightmare, relative to standard IRT. IRT, imagery rehearsal therapy; REM, rapid eye movement.

https://doi.org/10.1371/journal.pbio.3002684.g004

This neuroimaging signature was a key first step in answering a more fundamental question of whether other species dream. Of course, animals cannot provide verbal dream reports, making proof of the dream process difficult to ascertain for anyone other than humans. Evidence from the study of animal models of REM behavior disorder (RBD) provides added clues. Human RBD is a disorder characterized by dream enactment behaviors caused by the loss of muscle paralysis that accompanies the dreaming state of REM sleep [ 238 ]. Commonly violent, these movements may endanger the patient and their bed partners and, as recently affirmed, can reliably anticipate Parkinson’s disease [ 239 ]. Genetic, surgical, and pharmacological manipulation of the neural mechanisms that otherwise instigate muscle paralysis in rodents and cats results in remarkably similar behavioral repertoires during REM sleep, suggesting the possibility of dreams in animals (although there remains debate as to the acceptance of this premise [ 240 , 241 ]).

However, knowing the neural brain signature of human REM sleep that is associated with dreaming, scientists have started to ask whether a similar, objective neural signature could be found in other species and are getting closer to positive proof. The first fMRI-measured indications were recently published in Columba livia (pigeons). The researchers imaged the pigeon brains during the waking state and then again during REM sleep. What emerged was a strikingly similar pattern of brain activity to that associated with the experience of dreaming in humans; increased neural activity in visual regions, areas of the motor cortex, and subcortex, together with regions that regulate emotional affective states [ 242 ]. Of course, this finding does not prove that pigeons dream, but it does suggest that pigeons, despite their evolutionary divergence from mammals, nevertheless express a REM sleep neural pattern resembling that of humans, who do dream. Since neuroimaging methods in humans are fast becoming capable of deconstructing and then visually reconstructing the subjective waking experience of humans [ 243 – 245 ], a similar visual reconstruction of pigeon REM sleep brain activity may soon be on the horizon.

Not only does the brain show surges in stereotypical activity during human REM sleep, but so too do the peripheral nervous system, respiratory system, and vascular system [ 246 ]. A surprising recent discovery was made in cephalopods, specifically octopi, who have no central structured brain. During their offline state of sleep, the researchers systematically observed very clear, cycling swells of nervous system activity that repeated in bouts (approximately 1 minute) that are now believed to potentially be primitive REM sleep [ 247 , 248 ]. Also matching human REM sleep dreaming, it was harder to provoke the octopi to respond during these REM-like, fast-breathing, neural activation cycles relative to when awake [ 247 ]. Uniquely, these sleeping surges involved rapid pulsating body movements and synchronized changes in skin patterning. While this too does not prove dreaming, it is of note that octopi typically alter their skin patterning for camouflage during situations of threat and mating, both themes (threat and sex) that are present in human dreams [ 249 , 250 ].

Why brains dream

The “why” of human dreaming has been one of the most contentious, and fiendishly difficult, questions to answer scientifically. Although subtle in distinction, to establish a function of dreaming, one has to determine that any such benefit is not simply that of the underlying biological sleep state from whence those dreams came (e.g., REM sleep) but is instead specific to the dream itself. Using this framework, 2 main functions of dreaming (above and beyond sleep or REM sleep) have so far emerged: associative memory and creativity, and emotional processing and mood recalibration.

Memory, association, and creativity.

Although sleep is documented to boost learning and memory, only recently has dreaming been understood in terms of information processing independent of sleep. The benefits linked to dreaming are arguably even more powerful than the simple strengthening of individual facts that takes place during NREM sleep. Dreams can help interconnect large amounts of information, such that an individual wakes with a revised mind-wide web of associations capable of creatively divining solutions to problems previously faced while awake.

One recent study affirming this memory benefit assessed how efficiently individuals were able to weave together different memory components of a virtual maze they had been initially exposed to [ 251 ]. Those participants who obtained sleep after the learning phase were far better at assimilating the individual maze elements into a coherent whole, denoted by participants navigating their way through the maze faster, relative to a group that did not sleep during this time. This alone was not proof that dreaming itself was necessary. For that, researchers obtained dream reports throughout the sleep phase of those in the sleep group. Participants who slept and reported dreaming about the maze demonstrated a 10-fold improvement in navigation upon awakening, relative to those participants who slept, and still dreamt, but did not dream about the maze itself. It was not, therefore, enough to sleep or even to dream. Individuals had to dream about the waking problem itself in order to gain the associative memory benefit helping them to navigate the maze.

The process by which the dreaming brain accomplishes information assimilation, abstraction, and creativity is not completed in a single night. When studying dream content and waking life events systematically, information that individuals experience is most strongly integrated into their dreams over the first 2 nights, after which that information reprocessing appears to fade [ 252 , 253 ] ( Fig 4B ). Yet, these waking events then unexpectedly but very reliably resurface again 5 to 7 nights later—a phenomenon known as the “dream lag” effect [ 254 ]. These findings suggest that the conscious act of dreaming, and perhaps its memory function, evolves in 2 distinct temporal waves. The end product of these processes is arguably the difference between knowledge (learning individual facts, largely the role of NREM sleep [ 255 ]) and wisdom (knowing what they mean when we put them together, the role of conscious dreaming). Indeed, there is no shortage of science-related anecdotes of dream-instigated creativity. Examples include the dreams of Otto Loewi, which inspired experiments that led to his Nobel Prize–winning discovery of neurochemical transmission [ 256 ], and the equally impressive dream-inspired creative insights gifting Dmitri Mendeleev the elemental, universal (in the literal sense), conception of the periodic table of elements. Little wonder the advice is never to “stay awake on a problem.”

Emotional processing.

Posttraumatic stress disorder (PTSD), which reflects an inability of the brain to process and ultimately overcome a mentally damaging event, epitomizes the disability that occurs when the brain’s otherwise normal ability to resolve and move past difficult, painful experiences becomes impaired. Reactive depression to a specific event, such as bereavement or divorce, offers another clinical example of challenging mental health resolution. Dreaming appears to be one mechanism through which such emotional restitution (or overnight therapy) is accomplished [ 175 ]. Although Sigmund Freud arguably opined some version of this dream benefit [ 257 ], it was seminal works by Rosalind Cartwright and her colleagues in the 1990s that provided initial, scientifically credible evidence. Cartwright studied individuals with reactive depression, assessing their sleep and dream content, and tracking their clinical progress over time. Patients with depression exhibit significantly fewer dream reports relative to controls [ 258 , 259 ], and the more severe the patient rated their depression, the fewer dream reports they mustered [ 260 ]. Yet, it was what the patients were dreaming about, more than simply if they dreamt, that predicted recovery. Patients who ultimately overcame their depression, accomplishing remission a year later, were dreaming expressly about the trigger of their depression (i.e., the content of their dream), relative to those who were dreaming, yet not about the inciting experience as much [ 261 , 262 ]. Adding to this evidence, recent data have confirmed that the negative and positive emotions nested within the dream content predict next-day waking mood changes [ 263 ], with negative dreams increasing negative mood and vice versa. Thus, more than just the state of REM sleep, indeed more than the act of dreaming, it seems that the content of one’s dreams, and their emotionality, offers a form of nocturnal emotional first aid [ 264 ].

Understanding how dreams are curated and used by the brain has led to the development of new dream therapies, such as imagery rehearsal therapy (IRT), specifically targeting the most distressing dreams common in nightmare disorder and prevalent in PTSD [ 265 ]. IRT is a cognitive-behavioral technique aimed at reducing nightmares by modifying the content of distressing dreams. Individuals learn to “rescript” and mentally rehearse revised versions of their nightmares while awake, which helps transform the narrative and reduce the frequency and intensity of distressing dreams ( Fig 4C ). For example, having been in a serious car accident, someone might say they have a terrible repeating nightmare where they are unable to steer their car out of the way of incoming traffic, the brakes stop working, and then BANG … they wake up utterly distraught. The therapist will ask them to imagine alternative endings to their nightmare (the imagery part). So, in our example, perhaps they now reimagine a different ending where they realize they can reach down and gently use the handbrake to slow the car down. Next is the rehearsal part, where patients would rehearse this less distressing alternate ending daily for a couple of weeks in the hope of modifying and updating nightmare memories. Indeed, in a recent study using IRT, patients with nightmare disorder experienced a significant reduction in their nightmare frequency [ 266 ].

However, the therapeutic potential of IRT was even greater. In a second group of patients, the researchers asked participants to rehearse their alternative endings while listening to a pleasing piano chord played every 10 seconds in the background. Then, over the ensuing 2 weeks of the study, that same chord was played to participants at sub-awakening volume whenever they entered REM sleep at night. The purpose was to trigger the memory of those rehearsed alternative endings when nightmares often manifest. This dual manipulation strategy resulted in an even greater reduction in nightmare frequency. Indeed, they experienced an 80% greater relative reduction in nightmare frequency compared with the group that received IRT alone. Moreover, these sound-paired participants also reported a 2-fold greater increase in the number of positive emotions in their dreams, relative to the control group. Even more remarkable, the added benefits of the combined IRT and sound protocol were still significant in a 3-month follow-up, despite the fact participants were no longer receiving any cues during the night. Such advances illuminate a path forward in altering dream content to better facilitate the innate “overnight therapy” of dreams long after awakening.

Peering into dreams

Until recently, an individual’s dreams have been their own: a private experience that one decides if and when to reveal to others. Using advanced fMRI scanning methods, new data suggest this may no longer be the case [ 267 ]. While awake inside the MRI scanner, participants viewed many different objects across category themes (faces, cars, houses, etc.), with scientists then training a machine-learning model on this waking “ground truth” data of brain activity. The participants then performed a second fMRI scanning session. Now they were allowed to fall asleep, and the researchers obtained dream reports from these scanned sleeping periods. With high statistical probability, and using only the brain activity, blind to what the individuals had been dreaming of, the fMRI scans were able to predict what the individuals had experienced in their dreams with 70% accuracy. More specifically, the scientists could predict the category themes the individuals were dreaming about; e.g., they could decode that the dream included a car, predicting the form of the dream someone else was having. However, they could still not predict the unique content of the dreams (e.g., the make or model of the car), that level of detailed knowledge remains private—the purview of the dream owners themselves, at least for now. Based on recent EEG findings focused on specific regional brainwave frequencies, that time may be closer than once believed [ 268 ]. These developments could give rise to significant privacy concerns, considering that EEG is increasingly applicable to the home environment, and in the future, perhaps might even be as commonplace as contemporary smart wristbands [ 269 ].

Although most people do not have volitional control over their dreams within dreams, some individuals do. Such volitional awareness of, and controlling choices and actions, is called lucid dreaming. The challenge has been to empirically prove such a seemingly unprovable assertion, considering that the lucid dreamer in question is asleep, and thus unable to communicate with scientists, paralyzed by the dream state. Yet, scientists have overcome this challenge by harnessing one of the few muscle groups spared from REM sleep paralysis; the extraocular eye muscles. It is, therefore, possible to train lucid dreamers in a pre-agreed-upon pattern of what is essentially eye movement Morse code. Using this, it enabled the participants to signal to scientists the moment when they gain lucid control of their dream and further signal what they claim to be doing as they were lucid dream [ 270 ].

One elegant experiment dispelling any doubt of lucidity combined this eye movement communication method with neuroimaging [ 271 ]. After signaling the initial state of lucidity when asleep inside the scanner, the participants provided a pre-agreed eye movement signal that they were about to deliberately clench their left hand in their dream, and another signal that they were then clenching their right hand. When compared to the waking “ground truth” brain activity of actual physical hand movement, the brain activity occurring during the claimed lucid dream hand movement was an unmistakable match. Thus, scientists obtained objective proof of the subjective claim of lucid dreaming.

Researchers have now gone further. Using these communication methods, they have had back-and-forth, real-time dialogues with lucid dreamers, in objectively convincing ways. After a participant indicated that they had gained lucidity, the experimenter posed simple mathematical questions to the dreamer (e.g., 8 minus 6) using either speakers or visual flashing codes that participants had previously learned [ 272 ]. The dreamer then responded using eye movements while still asleep in the lucid state (confirmed by EEG), providing their deliberated answer. The participants were able to respond correctly, with a level of accuracy far above chance. This finding offers further ratification of the lucid dreaming claim and indicates the ability of lucid dreamers to comprehend information in a volitionally conscious way, offering deliberate logical answers under willful control. While rudimentary, such evidence may open up the opportunity for sleep-dependent, and dream-dependent, interventions, boosting the innate benefits of dreaming to new realms.

Lessons from the diversity of sleep across species

Every organism that has been carefully studied to date sleeps. From vertebrates to boneless species such as jellyfish [ 273 ], octopuses [ 274 ], and even worms [ 275 ], sleep appears to be evolutionarily ancient, strongly conserved, and near universal. Yet, there is confusing controversy within this narrative of consistency. Being as strongly preserved across evolution as it is, one would assume that the amount of sleep, and how that sleep is structured, would similarly be consistent across species or, at the very least, more similar than different. The opposite is true: The only thing more axiomatic and surprising than the homogeneity of sleep across species is the heterogeneity of how sleep is expressed across and even within species. This is mirrored by the nearly equal numbers of hypotheses attempting to explain these differences. In this section, we outline long-standing evidence and several new discoveries seeking to decipher this perplexing heterogeneity ( Fig 5 ).

Sleep duration varies markedly across the entire animal kingdom, from invertebrates to mammals. In most invertebrates and fish, sleep is defined behaviorally (e.g., for fire ants [ 276 ] and Port Jackson sharks [ 277 ]). Physiological evidence of NREM sleep can be found in a few amphibian species (e.g., the common frog [ 278 ]), as well as in reptiles [ 279 ]. In birds and mammals, evidence of sleep includes physiological recordings of both REM and NREM sleep, often measured in the lab [ 280 – 282 ]. NREM, nonrapid eye movement; REM, rapid eye movement.

https://doi.org/10.1371/journal.pbio.3002684.g005

Sleep variability

In mammals, sleep duration can range from as little as 2 hours in elephants [ 283 ], to 20 hours in the little brown bat [ 282 ]—a 10-fold difference in sleep duration. Indeed, some [ 284 ] have pointed out how idiosyncratic sleep duration is by highlighting clever comparisons [ 284 ]. One example is the ground squirrel, which sleeps for 15.9 hours on average, while the degu, which is ranked within the same taxonomic order, sleeps for an average of just 7.7 hours. By contrast, animals from different taxonomic orders, such as the guinea pig and the baboon, sleep for an identical amount of time (9.4 hours).

Recent data have added a new dimension of sleep variability within the same species. Elephant seals sleep for a little over 2 hours when making their months-long trips at sea, yet once they return to the land, they will defy that trend and consistently sleep for 10 hours or more each day ( Fig 5 ) [ 285 ]. Similarly, male pectoral sandpipers reduce their sleep amount 2-fold when females are present and fertile, relative to their sleep during nonbreeding periods. This adaptive act of ecologically pressured sleep reduction comes with a benefit. Those birds that slept the least during the breeding period gave rise to the most offspring [ 286 ]. Therefore, just when a fixed sleep duration label for a given species had been assumed from short-term, in-laboratory evaluations, it turned out that sleep duration within the same animal is far from fixed when tracked longitudinally in the wild.

Beyond sleep duration, species also differ in how their brains obtain sleep. During their trans-oceanic migrations, birds can switch off an entire hemisphere of their brain, putting it into a deep sleep while the other half of the brain remains wide awake. This feature, termed “unihemispheric sleep,” allows the migrating birds to have an open eye (linked to the respective waking hemisphere) turned to face the direction of flight [ 280 ]. The other eye, connected to the sleeping hemisphere, is closed shut. Ducks use this same sleep adaptation in response to a different evolutionary pressure. When ducks are lined up in a row, those individuals at the far ends of the flock sleep unihemispherically, directing the open waking eye to the vulnerable side of the flock to monitor predatory threats, while the eye (and corresponding opposite hemisphere) facing inwards to the safety of the flock is closed due to sleep. Those ducks seated within the flock have the luxury of sleeping with both hemispheres, since 360° perimeter threat detection is covered by the 2 sentinel ducks sitting at each end of the flock [ 287 ]. Many aquatic mammals show similar unihemispheric sleep patterns, driven by the equally different evolutionary pressure of needing to continue surface breathing. Nevertheless, they still manage to accomplish their sleep needs without drowning, one-half of the brain at a time.

Satisfying one’s full sleep need while keeping one-half of the brain awake to continue waking activities would seem like an envious ability that humans do not possess. Or so it was thought. Recent reports have shown that humans do, in fact, perform a version of unihemispheric sleep, albeit one that does not afford us the ability to continue functioning as if one hemisphere is completely awake. Have you ever had the experience of feeling as though you did not sleep well in a strange new environment [ 288 ]? A study has shown that when individuals sleep in a new environment, one hemisphere of the brain sleeps in a more shallow state of deep NREM sleep than the other. As with the ducks, the interpretation is that the human brain adapted to a change in how it sleeps when the potential for threat increases. While not fully awake, half of the brain in the proposed threat detection mode of lighter sleep is more responsive to sensory stimuli [ 289 ].

Theories of sleep variability

Building on these findings, new theories have been set forth regarding the explanatory functions of how sleep developed across the tree of life. Specifically, since REM sleep appears to be exclusive to warm-blooded animals, it has been proposed that thermoregulation was the original evolutionary force behind the development of REM sleep as a novel state designed to maintain homeothermy while still accomplishing sleep [ 290 , 291 ]. Consistent with this view, brain temperature drops in homeotherms (including humans) as they go deeper into NREM sleep. However, this trend reverses during REM sleep, when brain temperature reliably increases. Thus, REM sleep is thought to have emerged due to the evolutionary need for a reheat cycle during sleep; otherwise, the cognitively slowed state of brain functioning and the impeded autonomic function often necessary upon waking up quickly would be unacceptable for survival and fitness. Thus, the evolutionary reason that REM sleep emerged in warm-blooded mammals and birds (the classes that show reliable REM sleep) was to protect against excessive central brain hypothermia that would otherwise occur by experiencing NREM sleep alone [ 291 ]. However, the recent discovery of a “proto” version of REM sleep in cold-blooded reptiles [ 279 , 292 , 293 ], zebrafish [ 294 ], and marine invertebrates (including cuttlefish and octopuses [ 247 , 248 ]) has challenged the REM sleep thermoregulation hypothesis. Instead, these new findings suggest that the features of REM sleep, from muscle paralysis to rapid eye movements and increased cortical activity, developed earlier than previously thought. Therefore, the evolutionary reason for developing REM sleep must have preceded the need for temperature regulation. As with all good new discoveries, these data have only led to more interesting, as yet unanswered, questions about the function of REM sleep. The initial evolutionary reason for the emergence of paradoxical sleep, or REM sleep, therefore, still remains a paradox.

Even theories that sought to explain the variability in sleep duration across species, above and beyond the individual stages, remain controversial. A prominent and simple first theory was that brain size is the explanatory factor. The brain is, after all, a disproportionately demanding metabolic organ, and this size-related cost may, therefore, explain differences in sleep amount. Not so. The variability in sleep amount across species is not explained by brain size nor is it explained by cognitive ability [ 295 ]. Modified theories focused next on metabolic rate. One may logically predict that the more metabolically active a species, the more sleep (i.e., energy savings) it requires. Yet, metabolic rate only marginally accounts for variability in sleep amount, and even there, the association is in the opposite direction. Species with a high metabolic rate sleep less than those with a lower rate [ 284 ]. The current explanation is that more metabolically active species must spend more time awake foraging for food to satisfy their greater caloric demand and, thus, sleep less [ 2 , 291 ]. Here, too, as in the case of the flocking ducks, predatory risk further shapes sleep variability. Analysis of sleep duration across 58 species of mammals indicated that indeed those exposed to higher predatory risk sleep less, even when correcting for the size of the animal [ 295 ]. But since predation risk and being a herbivore tend to correlate, which factor is the more important is still an open question. One especially interesting species is the omnivore baboon ( Papio anubis ), which is subject to nightly predation risk imposed by leopards and lions. To mitigate the risk, and similar to the ducks, the baboons sleep in groups and also alternate sleep locations, 2 modifications that tend to compromise their sleep amount due to, what seems like, the first night effect (described for humans above) and awakenings caused by fellow baboons [ 296 ]. Despite the survival benefit of sleeping close to conspecifics, the price, in the form of insufficient sleep, has been observed across many mammals sleeping in the wild [ 295 ].

These are just some of the many examples of theories seeking to explain the heterogeneity of sleep among species. What all of these examples (from unihemispheric sleep to a 10-fold difference in sleep needs) have taught us is perhaps obvious, but worth reiteration: If sleep were dispensable and, thus, optional, or even if certain stages of sleep were desirable but not required, evolutionary pressures would have led to sleep, or a specific stage of sleep, being forfeited a long time ago. Nevertheless, the fact that sleep has consistently persevered throughout the evolution process, and done so in ingenious ways (within an individual, and across groups of individuals), serves to reinforce the conclusion that sleep is a critical necessity, serving numerous functions within and across species. This may not be so surprising, considering we have long recognized the polyfunctional nature of wakefulness.

Conclusions

This collection of recent discoveries not only affirms the role of sleep as a biological life-sustaining necessity but also extends the polyfunctional nature of sleep and the conscious state of dreaming in unexpected ways. These include DNA repair, immune function governance, effects on the gut microbiota, brain cleansing, controlling and enhancing complex social and emotional functioning, novel means of memory optimization, and the co-opting of divergent creativity. Moreover, through a growing understanding of basic sleep physiology, mechanism, and function, a plethora of new technologies are emerging that are capable of manipulating and enhancing human sleep physiology. As a result, there is a distinct possibility in the future that humans will be able to therapeutically manipulate sleep in precise ways for the treatment of specific diseases and disorders. These may range from regulating the gut microbiota to managing the mental health of an individual, slowing brain aging and its pathologies, aiding in trauma resolution, and even facilitating prosocial engagement in the face of a growing loneliness epidemic [ 297 – 299 ].

Apart from this, a different discussion theme emerges from the new wave of research discoveries, i.e., the elemental “why” of sleep, and more specifically, how researchers conceptualize the question, aside from any answers they arrive at. Wakefulness, the antithesis of sleep, becomes a meaningful lens through which to explore a claimed sleep-dependent benefit/process. In this framework of questioning, the guiding principle has been to search for a sleep function that cannot be served by wakeful rest. The query, therefore, becomes, for any functions thought to be ascribed to sleep, is there any evidence that this function can be supported by wakefulness, and if not, why not?

Another nonmutually exclusive framework for answering the question of sleep’s why is in its absence. Classical methods of total and selective sleep deprivation were scientifically limited based on the confounds of the deprivation methods used, such as stress, or the fact that selective deprivation of a sleep stage also meant that total sleep time was defacto reduced. Now, however, there are much more sophisticated methods that obviate many of these concerns and offer stronger causal affirmations. A good example is the method of sub-awakening auditory tones. Using this method, the individual is selectively deprived of deep NREM sleep in a specific brain area by the tones that lift them into lighter NREM sleep without waking them, and so total NREM sleep duration is preserved [ 300 ]. Another example is using implanted electrodes in animal models. Here, the electrodes are used to selectively disrupt neural events, such as forward memory-sequence replay during NREM sleep (the replaying of the order of memory-cell firing that was coded during initial spatial learning while the animal was awake), thereby demonstrating a causal dependence on a physiological sleep mechanism for memory consolidation [ 301 ]. As new methodological advances grow in their nuance and ability to selectively excise other stages of sleep, or even specific electrical brain-wave oscillations, the dissection of the “why” of sleep dependency will become ever more concrete. And “dependent” not only in the sense of sleep versus wake, but also of one sleep state relative to another, or even to the extent of one specific brain region’s experiences of a sleep-oscillation state relative to other brain regions.

More generally, the revelations brought forth by these new, highly diverse functions of sleep do not negate the possibility that one consensus and common function of sleep nevertheless exists across species. There may very well be a singular (original and/or common) function of sleep that transcends taxonomy. Moreover, the notions that a single common function of sleep exists, while additional multiple functions of sleep have later evolved across time, are not mutually exclusive or antagonistic.

As the polyfunctional view of sleep grows, another fruitful framework is that of the interdependence and interconnectedness of different sleep functions that achieve benefits to the organism greater than the sum of each part. Here again, it is something that has long been accepted regarding many of the functions of wakefulness. For example, without sleep’s interconnected support, the ensuing free radical damage caused by sleep deficiency may increase inflammation, which, in turn, leads to sickness behavior, which consequently triggers social withdrawal and loneliness in the sleep-deprived individual. Another possible example would be the emotional and social changes in behavior caused by sleep loss that impair the immune system, which leads to worse gut microbiome health and, through afferent vagal signaling, alters mood and emotional states, each of which only further disrupts sleep, leading to an interconnected negative spiral. For sleep and its functions, cinematically speaking, it is “Everything, Everywhere, All At Once.”

• View Article
• PubMed/NCBI
• Google Scholar
• 170. Mehrabian A. Nonverbal Communication. 1st ed. Routledge; 2017.
• 244. Takagi Y, Nishimoto S. High-resolution image reconstruction with latent diffusion models from human brain activity. bioRxiv [Preprint]. 2023. p. 2022.11.18.517004. https://doi.org/10.1101/2022.11.18.517004
• 257. Freud S. On Dreams. W. W. Norton & Company; 1989.
• 269. Azemi E, Moin A, Pragada A, Lu JH-C, Powell VM, Minxha J, et al. Biosignal Sensing Device Using Dynamic Selection of Electrodes. United States patent 20230225659:A1. 2023. Available from: https://patentimages.storage.googleapis.com/e2/4d/92/a20ceacf02d9db/US20230225659A1.pdf

A monthly newsletter from the National Institutes of Health, part of the U.S. Department of Health and Human Services

Search form

Print this issue

Good Sleep for Good Health

Get the Rest You Need

Sometimes, the pace of modern life barely gives you time to stop and rest. It can make getting a good night’s sleep on a regular basis seem like a dream.

But sleep is as important for good health as diet and exercise. Good sleep improves your brain performance, mood, and health.

Not getting enough quality sleep regularly raises the risk of many diseases and disorders. These range from heart disease and stroke to obesity and dementia.

There’s more to good sleep than just the hours spent in bed, says Dr. Marishka Brown, a sleep expert at NIH. “Healthy sleep encompasses three major things,” she explains. “One is how much sleep you get. Another is sleep quality—that you get uninterrupted and refreshing sleep. The last is a consistent sleep schedule.”

People who work the night shift or irregular schedules may find getting quality sleep extra challenging. And times of great stress—like the current pandemic—can disrupt our normal sleep routines. But there are many things you can do to improve your sleep.

Sleep for Repair

Why do we need to sleep? People often think that sleep is just “down time,” when a tired brain gets to rest, says Dr. Maiken Nedergaard, who studies sleep at the University of Rochester.

“But that’s wrong,” she says. While you sleep, your brain is working. For example, sleep helps prepare your brain to learn, remember, and create.

Nedergaard and her colleagues discovered that the brain has a drainage system that removes toxins during sleep.

“When we sleep, the brain totally changes function,” she explains. “It becomes almost like a kidney, removing waste from the system.”

Her team found in mice that the drainage system removes some of the proteins linked with Alzheimer’s disease. These toxins were removed twice as fast from the brain during sleep.

Everything from blood vessels to the The system that protects your body from invading viruses, bacteria, and other microscopic threats. immune system uses sleep as a time for repair, says Dr. Kenneth Wright, Jr., a sleep researcher at the University of Colorado.

“There are certain repair processes that occur in the body mostly, or most effectively, during sleep,” he explains. “If you don’t get enough sleep, those processes are going to be disturbed.”

Sleep Myths and Truths

How much sleep you need changes with age. Experts recommend school-age children get at least nine hours a night and teens get between eight and 10. Most adults need at least seven hours or more of sleep each night.

There are many misunderstandings about sleep. One is that adults need less sleep as they get older. This isn’t true. Older adults still need the same amount. But sleep quality can get worse as you age. Older adults are also more likely to take medications that interfere with sleep.

Another sleep myth is that you can “catch up” on your days off. Researchers are finding that this largely isn’t the case.

“If you have one bad night’s sleep and take a nap, or sleep longer the next night, that can benefit you,” says Wright. “But if you have a week’s worth of getting too little sleep, the weekend isn’t sufficient for you to catch up. That’s not a healthy behavior.”

In a recent study, Wright and his team looked at people with consistently deficient sleep. They compared them to sleep-deprived people who got to sleep in on the weekend.

Both groups of people gained weight with lack of sleep. Their bodies’ ability to control blood sugar levels also got worse. The weekend catch-up sleep didn’t help.

On the flip side, more sleep isn’t always better, says Brown. For adults, “if you’re sleeping more than nine hours a night and you still don’t feel refreshed, there may be some underlying medical issue,” she explains.

Sleep Disorders

Some people have conditions that prevent them from getting enough quality sleep, no matter how hard they try. These problems are called sleep disorders.

The most common sleep disorder is insomnia. “Insomnia is when you have repeated difficulty getting to sleep and/or staying asleep,” says Brown. This happens despite having the time to sleep and a proper sleep environment. It can make you feel tired or unrested during the day.

Insomnia can be short-term, where people struggle to sleep for a few weeks or months. “Quite a few more people have been experiencing this during the pandemic,” Brown says. Long-term insomnia lasts for three months or longer.

Sleep apnea is another common sleep disorder. In sleep apnea, the upper airway becomes blocked during sleep. This reduces or stops airflow, which wakes people up during the night. The condition can be dangerous. If untreated, it may lead to other health problems.

If you regularly have problems sleeping, talk with your health care provider. They may have you keep a sleep diary to track your sleep for several weeks. They can also run tests, including sleep studies. These look for sleep disorders.

Getting Better Sleep

If you’re having trouble sleeping, hearing how important it is may be frustrating. But simple things can improve your odds of a good night’s sleep. See the Wise Choices box for tips to sleep better every day.

Treatments are available for many common sleep disorders. Cognitive behavioral therapy can help many people with insomnia get better sleep. Medications can also help some people.

Many people with sleep apnea benefit from using a device called a CPAP machine. These machines keep the airway open so that you can breathe. Other treatments can include special mouthguards and lifestyle changes.

For everyone, “as best you can, try to make sleep a priority,” Brown says. “Sleep is not a throwaway thing—it’s a biological necessity.”

Popular Stories

When Blood Vessels Grow Awry

Buffering Childhood Stress

The Mighty Fruit Fly

Beyond Basic Blood Tests

NIH Office of Communications and Public Liaison Building 31, Room 5B52 Bethesda, MD 20892-2094 [email protected] Tel: 301-451-8224

Editor: Harrison Wein, Ph.D. Managing Editor: Tianna Hicklin, Ph.D. Illustrator: Alan Defibaugh

Attention Editors: Reprint our articles and illustrations in your own publication. Our material is not copyrighted. Please acknowledge NIH News in Health as the source and send us a copy.

For more consumer health news and information, visit health.nih.gov .

For wellness toolkits, visit www.nih.gov/wellnesstoolkits .

Save BIG on mattresses this July 4th! Shop the best deals .

Why Do We Need Sleep?

Contributing Writer

Lucy Bryan is a writer and editor with more than a decade of experience in higher education. She holds a B. A. in journalism from the University of North Carolina at Chapel Hill and an M.F.A. in creative writing from Penn State University.

Want to read more about all our experts in the field?

Dr. Brandon Peters

Sleep Physician, Sleep Psychiatry Expert

Brandon R. Peters, M.D., FAASM, is a double board-certified neurologist and sleep medicine specialist and fellow of the American Academy of Sleep Medicine who currently practices at Virginia Mason Franciscan Health in Seattle. He is a leading voice in sleep medicine who works at the cutting edge of medicine and technology to advance the field.

Sleep Foundation

Fact-Checking: Our Process

The Sleep Foundation editorial team is dedicated to providing content that meets the highest standards for accuracy and objectivity. Our editors and medical experts rigorously evaluate every article and guide to ensure the information is factual, up-to-date, and free of bias.

The Sleep Foundation fact-checking guidelines are as follows:

• We only cite reputable sources when researching our guides and articles. These include peer-reviewed journals, government reports, academic and medical associations, and interviews with credentialed medical experts and practitioners.
• All scientific data and information must be backed up by at least one reputable source. Each guide and article includes a comprehensive bibliography with full citations and links to the original sources.
• Some guides and articles feature links to other relevant Sleep Foundation pages. These internal links are intended to improve ease of navigation across the site, and are never used as original sources for scientific data or information.
• A member of our medical expert team provides a final review of the content and sources cited for every guide, article, and product review concerning medical- and health-related topics. Inaccurate or unverifiable information will be removed prior to publication.
• Plagiarism is never tolerated. Writers and editors caught stealing content or improperly citing sources are immediately terminated, and we will work to rectify the situation with the original publisher(s)
• Although Sleep Foundation maintains affiliate partnerships with brands and e-commerce portals, these relationships never have any bearing on our product reviews or recommendations. Read our full Advertising Disclosure for more information.

Table of Contents

Why Getting Enough Sleep Is Important

The science behind why we sleep, how much sleep do i need, the effects of a lack of sleep, how to always get a good night’s sleep.

If you’ve stayed awake all night—by choice, out of necessity, or in spite of your efforts to sleep—you know just how critical sleep is to your wellbeing. Everyone needs sleep, but about one in three American adults don’t get enough of it.

The consequences of sleep deprivation are serious, so it’s worth learning why sleep matters, how it works, and how to give yourself the best chances of getting a good night’s sleep.

Sleep is an essential function that allows your body and mind to recharge, leaving you refreshed and alert when you wake up. Healthy sleep also helps the body remain healthy and stave off diseases. Without enough sleep, the brain cannot function properly, impairing your abilities to concentrate, think clearly, and process memories.

Sleep serves a variety of important physical and psychological functions, including:  

• Learning and memory consolidation: Sleep helps with focus and concentration—and it allows the brain to register and organize memories —all of which are vital to learning.
• Emotional regulation: Sleep helps people regulate their emotions Trusted Source National Library of Medicine, Biotech Information The National Center for Biotechnology Information advances science and health by providing access to biomedical and genomic information. View Source and better manage the physical and psychological effects of stress.
• Judgment and decision making: Sleep influences a person’s ability to recognize danger and threats. Trusted Source National Library of Medicine, Biotech Information The National Center for Biotechnology Information advances science and health by providing access to biomedical and genomic information. View Source Healthy sleep supports sound judgment, good decision making, and other executive functions.
• Problem solving: Research shows that “sleeping on” a complex problem improves a person’s chance of solving it. Trusted Source National Library of Medicine, Biotech Information The National Center for Biotechnology Information advances science and health by providing access to biomedical and genomic information. View Source
• Energy conservation: Sleep allows people to conserve energy through an extended period of reduced activity.
• Growth and healing: Sleep provides the release of growth hormone necessary for the body’s tissues to grow and repair damage.
• Immunity: Sleep supports immune function , allowing the body to fight off diseases and infections.

Human beings, like all species on Earth, evolved to survive and thrive on a planet with a 24-hour cycle of day and night. According to some theories of sleep, Trusted Source National Library of Medicine, Biotech Information The National Center for Biotechnology Information advances science and health by providing access to biomedical and genomic information. View Source sleeping in one consolidated block at night allowed early humans to simultaneously avoid predators, conserve energy, and meet their need for rest. It also kept them from having to adapt to life in two very different conditions—daylight and darkness.

The biological patterns that help humans live according to the 24-hour day-night cycle are called circadian rhythms . These rhythms work alongside the sleep drive —a desire to sleep that grows in intensity the longer a person has been awake—to cause people to feel sleepy at night and alert in the morning. 

Circadian rhythms, including the sleep-wake cycle, operate according to environmental cues. Every evening, as darkness sets in, the body begins releasing the sleep hormone melatonin—and every morning, with the arrival of light , the body’s melatonin levels become undetectable. An evening drop and morning rise in body temperature accompanies this cycle, enhancing sleepiness and alertness at the right times.

Stages of Sleep

Our sleep architecture—that is, the way the body cycles through specific stages of sleep —enables the beneficial processes that occur during sleep, such as healing and learning. There are three non-rapid eye movement (non-REM) stages of sleep followed by rapid eye movement (REM), the final stage of sleep. Experiencing all four usually takes anywhere from 1.5 to 2 hours. Trusted Source UpToDate More than 2 million healthcare providers around the world choose UpToDate to help make appropriate care decisions and drive better health outcomes. UpToDate delivers evidence-based clinical decision support that is clear, actionable, and rich with real-world insights. View Source

• Stage N1: This is the lightest stage of sleep, and it usually only lasts a few minutes.
• Stage N2: Healthy adults usually spend about half of the night in N2 sleep. While brain activity slows, there are bursts of activity that may help with memory retention and learning.
• Stage N3: N3 sleep, also called “slow wave sleep” or “deep sleep,” helps a person wake up feeling refreshed. During this stage, blood pressure lowers, heart rate and breathing rate slow, and the body secretes growth hormone. People generally spend about 10% to 20% of the night in this stage. 
• REM Sleep: As its name suggests, people’s eyes intermittently move rapidly during this sleep stage. Most vivid dreaming takes place during REM sleep, and skeletal muscles become temporarily paralyzed to prevent a person from acting out their dreams. Memory consolidation occurs in this stage. It accounts for 20% to 25% of a typical night of sleep, with more of it occurring towards morning.

Healthy individuals cycle through all four stages of sleep multiple times a night. Regular sleep disruptions, as well as sleep disorders that affect sleep architecture like sleep apnea, can have serious consequences for physical health and mental health .

Experts generally recommend that adults get at least seven hours of sleep per night. Trusted Source National Library of Medicine, Biotech Information The National Center for Biotechnology Information advances science and health by providing access to biomedical and genomic information. View Source However, sleep needs can vary dramatically from person to person. Your activity level, your health status, and many other factors influence how much sleep you need , but the optimal number of hours typically falls within a specific range depending on your age and stage in life.

Not getting the amount of sleep your body needs can have serious consequences. Just one sleepless night can make it harder for you to focus and think clearly, and you might feel tired or sluggish during the day. You’re more likely to feel irritable and to exercise poor judgment when you haven’t had enough sleep. And sleep deprivation significantly elevates your risk Trusted Source UpToDate More than 2 million healthcare providers around the world choose UpToDate to help make appropriate care decisions and drive better health outcomes. UpToDate delivers evidence-based clinical decision support that is clear, actionable, and rich with real-world insights. View Source of making a mistake at work or having a car accident.

Long-term sleep deprivation carries all these risks and more. Chronic insufficient sleep may:

• Suppress your immune system, increasing your susceptibility to sickness and infection 
• Increase your risk of developing heart problems, type 2 diabetes, and high blood pressure 
• Interfere with your metabolism and elevate your risk for obesity 
• Cause your relationships to suffer at work and at home 
• Lead to depression and anxiety 

The effects of sleep debt compound quickly, so the sooner you can address sleep difficulties, the better.

The good news is that many sleep problems improve and even disappear when you take the right steps to treat them. Start by implementing healthy sleep hygiene practices at home.

• Get at least 20 minutes of exposure to natural light in the morning. 
• Commit to a regular sleep schedule.
• Adopt a relaxing bedtime routine.
• Make sure your bedroom environment is cool, dark, quiet, and comfortable.
• Avoid electronics with screens in the hour before bed.
• Exercise regularly and early in the day. 
• Avoid alcohol, nicotine, and caffeine in the hours before bed. 

If you have trouble sleeping even after taking these steps, contact your doctor. With the right treatments, you can get the sleep your body needs.

• New Research Evaluates Accuracy of Sleep Trackers
• Listening to Calming Words While Asleep Boosts Deep Sleep
• Distinct Sleep Patterns Linked to Health Outcomes
• Association Between Sleep Duration and Disturbance with Age Acceleration

About Our Editorial Team

Lucy Bryan, Contributing Writer

Medically Reviewed by

Dr. Brandon Peters, Sleep Physician, Sleep Psychiatry Expert

References 7 sources.

Vandekerckhove, M., & Wang, Y. L. (2017). Emotion, emotion regulation and sleep: An intimate relationship. AIMS neuroscience, 5(1), 1–17.

Khan, M. A., & Al-Jahdali, H. (2023). The consequences of sleep deprivation on cognitive performance. Neurosciences (Riyadh, Saudi Arabia), 28(2), 91–99.

Sio, U. N., Monaghan, P., & Ormerod, T. (2013). Sleep on it, but only if it is difficult: effects of sleep on problem solving. Memory & cognition, 41(2), 159–166.

Freiberg A. S. (2020). Why We Sleep: A Hypothesis for an Ultimate or Evolutionary Origin for Sleep and Other Physiological Rhythms. Journal of circadian rhythms, 18, 2.

Kirsch, D. (2024, March). Stages and architecture of normal sleep. In S. Harding & A.Eichler (Ed.). UpToDate.

Consensus Conference Panel, Watson, N. F., Badr, M. S., Belenky, G., Bliwise, D. L., Buxton, O. M., Buysse, D., Dinges, D. F., Gangwisch, J., Grandner, M. A., Kushida, C., Malhotra, R. K., Martin, J. L., Patel, S. R., Quan, S. F., Tasali, E., Non-Participating Observers, Twery, M., Croft, J. B., Maher, E., … Heald, J. L. (2015). Recommended amount of sleep for a healthy adult: A joint consensus statement of the American Academy of Sleep Medicine and Sleep Research Society. Journal of Clinical Sleep Medicine, 11(6), 591–592.

Maski, K. (2024, March). Insufficient sleep: Evaluation and management. In T. Scammell & A. Eichler (Ed.). UpToDate.

Learn More About How Sleep Works

How to Become a Morning Person

How Much Sleep Do You Need?

How Memory and Sleep Are Connected

What Causes Excessive Sleepiness?

What Causes Restless Sleep?

Biphasic Sleep: What It Is And How It Works

Polyphasic Sleep: Benefits and Risks

Sleep Inertia: How to Combat Morning Grogginess

REM Rebound: Causes and Effects

Do Moon Phases Affect Your Sleep?

Alpha Waves and Sleep

How Age Affects Your Circadian Rhythm

How Is Sleep Different For Men and Women?

Circadian Rhythm

Chronotypes: Definition, Types, & Effect on Sleep

Sleep Drive and Your Body Clock

8 Health Benefits of Sleep

Daylight Saving Time: Everything You Need to Know

How To Get a Good Night’s Sleep in a Hotel

Does Napping Impact Your Sleep at Night?

Does Daytime Tiredness Mean You Need More Sleep?

Why Do I Wake Up at 3 am?

Sleep Debt: The Hidden Cost of Insufficient Rest

Sleep Satisfaction and Energy Levels

How Sleep Works: Understanding the Science of Sleep

What Makes a Good Night's Sleep

What Happens When You Sleep?

Sleep and Social Media

Adenosine and Sleep: Understanding Your Sleep Drive

Oversleeping

Hypnagogic Hallucinations

Hypnopompic Hallucinations

What All-Nighters Do To Your Cognition

Long Sleepers

How to Wake Up Easier

Sleep Spindles

Does Your Oxygen Level Drop When You Sleep?

100+ Sleep Statistics

Short Sleepers

How Electronics Affect Sleep

Myths and Facts About Sleep

What’s the Connection Between Race and Sleep Disorders?

Sleep Latency

Microsleep: What Is It, What Causes It, and Is It Safe?

Light Sleeper: What It Means and What To Do About It

Other articles of interest, best mattresses, sleep testing and solutions, bedroom environment, sleep hygiene.

An official website of the United States government

Here’s how you know

Official websites use .gov A .gov website belongs to an official government organization in the United States.

Secure .gov websites use HTTPS A lock ( A locked padlock ) or https:// means you’ve safely connected to the .gov website. Share sensitive information only on official, secure websites.

• Heart-Healthy Living
• High Blood Pressure
• Sickle Cell Disease
• Sleep Apnea
• Information & Resources on COVID-19
• The Heart Truth®
• Learn More Breathe Better®
• Blood Diseases and Disorders Education Program
• Publications and Resources
• Blood Disorders and Blood Safety
• Sleep Science and Sleep Disorders
• Lung Diseases
• Health Disparities and Inequities
• Heart and Vascular Diseases
• Precision Medicine Activities
• Obesity, Nutrition, and Physical Activity
• Population and Epidemiology Studies
• Women’s Health
• Research Topics
• Clinical Trials
• All Science A-Z
• Grants and Training Home
• Policies and Guidelines
• Funding Opportunities and Contacts
• Training and Career Development
• Email Alerts
• NHLBI in the Press
• Research Features
• Ask a Scientist
• Past Events
• Upcoming Events
• Mission and Strategic Vision
• Divisions, Offices and Centers
• Advisory Committees
• Budget and Legislative Information
• Jobs and Working at the NHLBI
• Contact and FAQs
• NIH Sleep Research Plan
• Health Topics
• < Back To How Sleep Works
• Why Is Sleep Important?
• How Sleep Works
• Your Sleep/Wake Cycle
• Sleep Phases and Stages
• How Much Sleep Is Enough?

MORE INFORMATION

How Sleep Works Why Is Sleep Important?

Language switcher.

Sleep plays a vital role in good health and well-being throughout your life. The way you feel while you are awake depends in part on what happens while you are sleeping. During sleep, your body is working to support healthy brain function and maintain your physical health.

In children and teens, sleep also helps support growth and development. Getting inadequate sleep over time can raise your risk for chronic (long-term) health problems. It can also affect how well you think, react, work, learn, and get along with others. Learn how sleep affects your heart and circulatory system, metabolism , respiratory system, and immune system and how much sleep is enough.

This brochure describes the differences between the types of sleep needed to feel awake and to be healthy and offers tips for getting a good night’s sleep.

Heart and circulatory system

When you fall asleep and enter non-REM sleep , your blood pressure and heart rate fall. During sleep, your parasympathetic system controls your body, and your heart does not work as hard as it does when you are awake. During REM sleep and when waking, your sympathetic system is activated, increasing your heart rate and blood pressure to the usual levels when you are awake and relaxed. A sharp increase in blood pressure and heart rate upon waking has been linked to angina, or chest pain, and heart attacks .

People who do not sleep enough or wake up often during the night may have a higher risk of:

• Coronary heart disease
• High blood pressure

Hormones and sleep

Your body makes different hormones at different times of day. This may be related to your sleep pattern or your circadian clocks. In the morning, your body releases hormones that promote alertness, such as cortisol, which helps you wake up. Other hormones have 24-hour patterns that vary throughout your life; for example, in children, the hormones that tell the glands to release testosterone, estrogen, and progesterone are made in pulses at night, and the pulses get bigger as puberty approaches.

Metabolism and sleep

The way your body handles fat varies according to various circadian clocks, including those in the liver, fat, and muscle. For example, the circadian clocks make sure that your liver is prepared to help digest fats at appropriate times. Your body may handle fat differently if you eat at unusual times.

Studies have shown that not getting enough quality sleep can lead to:

• Higher levels of the hormones that control hunger, including leptin and ghrelin, inside your body
• Decreased ability to respond to insulin
• Increased consumption of food, especially fatty, sweet, and salty foods
• Decreased physical activity
• Metabolic syndrome

All of these contribute to overweight and obesity .

Respiratory and immune systems

During sleep, you breathe less often and less deeply and take in less oxygen. These changes can cause problems in people who have health problems such as asthma or chronic obstructive pulmonary disease (COPD) . Asthma symptoms are usually worse during early morning sleep. Likewise, breathing problems in people who have lung diseases such as COPD can become worse during sleep.

Sleep also affects different parts of your immune system, which become more active at different times of day. For example, when you sleep, a particular type of immune cell works harder. That is why people who do not sleep enough may be more likely to get colds and other infections.

Lung Health Basics: Sleep

People with lung disease often have  trouble sleeping. Sleep is critical to overall health, so take the first step to sleeping better: learn these sleep terms, and find out about treatments that can help with sleep apnea.

Problems with thinking and memory

Sleep helps with learning and the formation of long-term memories. Not getting enough sleep or enough high-quality sleep can lead to problems focusing on tasks and thinking clearly. Read our Sleep Deprivation and Deficiency page for more information on how lack of sleep affects performance of daily activities, including driving and schoolwork.

• Skip to main content
• Skip to secondary menu
• Skip to primary sidebar
• Skip to footer

A Plus Topper

Improve your Grades

Importance of Sleep Essay | Essay on Importance of Sleep for Students and Children in English

February 13, 2024 by Prasanna

Importance of Sleep Essay:  Sleep is one of the most important things you need to do for your body because it is your body’s way of recharging its batteries. When you begin to feel sleepy at night, it means that you have reached the limit that your body has, and you should sleep so that you do not over-exert yourself.

Many people don’t get enough sleep at night, mostly because so many of us have turned into night owls who love to do so many things at night instead of the daytime. These are terrible habits, and we must learn to get rid of them by paying attention to the importance of sleep. For example, a bad habit like this would be watching TV shows late at night despite knowing that we have to wake up early the next morning.

You can also find more  Essay Writing  articles on events, persons, sports, technology and many more.

Long and Short Essays on Importance of Sleep for Students and Kids in English

Let’s look at some essays of different, increasing word lengths to know and understand the importance of sleep. These ‘Importance of Sleep’ Essays can also be like your inspiration to write your essay about the same.

Short Essay on Importance of Sleep 150 Words in English

Short Essay on Importance of Computer is usually given to classes 1, 2, 3, 4, 5, and 6.

When we sleep, the brain recharges itself and heals our bodies in whichever parts we need healing. When we sleep, our blood vessels and circulatory system heal themselves. If you have a bruise, you will notice that it has healed a little bit when you go to sleep and wake up in the morning. Sleep does the same thing for the rest of the body as well, and it is essential to allow your batteries to charge while you heal yourself.

Many of us struggle with our sleep because of the prevalence of mobile phones and other addictive screens in our lives. Some severe problems can enter our lives when we do not get enough sleep. This can range from mental health problems like depression and anxiety to even physical ailments and issues like diabetes, cardiac arrest, obesity, high blood pressure, etc. We must be careful and get a good 6-8 hours of sleep every night.

The average hours that one adult should be sleeping every night is 8 hours, or you can give or take one or two hours. The problem with all the generations in the world is that there are so many disturbances around us that can easily distract us from what is essential. One such example of this is mobile phones – it is easy to get addicted to mobile phones that contain an entire world and keep scrolling through it instead of going to sleep.

It is essential to understand the reason why sleep is vital. Getting enough sleep helps heal your bodies from any pain or injuries; it betters your immune system, cognitive memory, and thinking capacity. Furthermore, getting adequate sleep is vital for keeping our hearts and other systems clean and with a good bill of health. Without getting a good number of hours worth of sleep at night, we are putting ourselves at the risk of mental health disruptions as well as physical disorders and problems such as depression, anxiety, heart attacks, obesity (leading to various other issues), and even exhaustion which can ultimately disrupt one’s life. We must get enough sleep to look and feel fresh and healthy every day.

Introduction

Many of us do not realise the importance that a good night’s sleep holds in our lives. It is so important to sleep well at night to prevent us from getting health problems which can be disruptive for our whole lives. Let’s talk a little bit more about the importance of sleep in our lives.

Healthy Living with Good Sleep

It is essential to sleep well to live a healthy life. There are many health benefits of getting a good night’s sleep, and there are many hindrances to when you don’t get a good night’s sleep. The benefits of good sleep are that it can boost your immune system, boost your cardiovascular health, improve our abilities to think and remember things more clearly, and contain our mental health by preventing some symptoms of anxiety and depression. Sleep also helps us out with containing our exhaustion of course, the best thing to do when you are tired is to go to sleep and regain the energy you need to carry forth with your life. Most importantly, sleeping well and sleeping enough helps prevent obesity, diabetes, heart problems, and various other issues.

We must all sleep for about 8 hours in our adult lives. It can be about an hour less or an hour more, but think about it this way – you must spend about one third to one-fourth of your day recharging your batteries to get ready for the remainder of the days.

You can also read many interesting facts equipped about the importance of sleep essay furthermore in the given here, Importance of sleep essay. Never miss it!

Importance of Sleep Essay 400 Words in English

Sleep is one of the most essential and inevitable things that we have to do in our lives. Whether you eat food or drink water, sleep is inevitable because it’s what the body does naturally. Sometimes it can be tough to get a full night’s sleep, but it is imperative to try.

The Trio of Good Health

We can deny nothing about the fact that there are three things we need to improve our lives – a good diet with tonnes of nutrition, an exercise routine, and, of course, a good night’s sleep every day. These are the three things that are very imperative in our lives to inculcate and follow. Sleeping well has impressive health benefits, such as improving our cardiovascular health and preventing obesity, which even come a lot of other problems. A balanced diet filled with nutritious foods helps us remain fit and healthy, and a good exercise plan will be good for the same, too. Sleeping enough also helps us out with our strength and performance during exercise. Thus, it is a good cycle that we should create for ourselves.

Benefits of Good Sleep

There are several benefits of getting a good sleep at night. It helps you maintain your body weight so that you do not become obese and add to this; there’s also the fact that people who sleep well at night often eat less than those who don’t, which also helps with the weight. Getting adequate sleep also increases your productivity by making you feel more energetic and giving you the time you need to rest. It also helps our lives be in a good mood, and good sleep puts a person in a good mood. Sleeping enough also allows our minds to function correctly and in a better way. Thus we can think better, and we also have a better memory power upon sleeping enough.

Getting adequate sleep is incredibly vital to our mental health and physical well-being. If we do not get enough sleep, we might get burnt out and not be able to carry out our lives in the way that we should be able to. Without the ability to do this, life can become painful and full of difficulties that may become complex over time. Thus, we must all take the initiative in our own lives to sleep on time and wake up on time to prevent any mental or physical blockages and hindrances.

Long Essay on Importance of Sleep 500 Words in English

Long Essay on Importance of Computer is usually given to classes 7, 8, 9, and 10.

Sleep is one of the most essential parts of our lives; still, most of us neglect it as though there’s nothing wrong with that. It is understandable that we barely ever get any time to rest when we have a hectic life. For so many of us workaholics, sleeping can even seem like something you can do later, that there are more things you can do in the time that you could be sleeping. However, working like this may be alright for a short while, but not getting enough sleep for a long-stretched period has been found to have terrible effects on the body in the long run. We must all learn how to take care of ourselves, and this begins by forming a good routine with an adequate amount of sleep inculcated in it, alongside a good diet and regular exercise.

It is a lesser-known fact that sleeping well and sleeping a fair amount of hours when we are supposed to supplements the maintenance of our weight – this means that if you sleep better, you’re less likely to put on more weight! This is corroborated because those who sleep more need fewer calories to function in a day, as they are more refreshed and energised and thus require less food to keep them afloat throughout the day calories mean less weight.

Sleep is when our body and brains regenerate, meaning that your blood vessels and your heart and the other parts of your body heal themselves while you are sleeping. Think about it this way – you are not doing anything, your eyes are closed, and at this time, your brain has no other work because you are not conscious of doing anything in particular that the brain needs to function for. Thus, this is the best time for your body to heal itself. You’ll notice that when you wake up after getting an injury the previous day, the bruises may have already begun to heal – scabs are created in the process of healing through the night while you sleep. Thus, sleep is so crucial for healing the body.

Getting your good 7-9 hours of sleep every night is imperative for our bodies to work well the next day. Sleeping removes the tiredness from our bodies, and it rejuvenates and re-energises us for the next day. With adequate sleep, we can focus on our work better, we can do more things in our day to make it more productive, and we will be able to think, read and do everything else much better through the course of the day with good sleep.

What Happens When We Don’t Sleep Well?

Not sleeping enough is one of the worst things that a person can do to their bodies. As mentioned before, sleeping is great for rejuvenating our bodies and healing our systems inside. So, it is the complete opposite that takes place when we don’t get enough sleep.

If we do not get enough sleep at night, we will end up with terrible health. Most of us end up binge-watching television shows, movies, and even things like YouTube videos at night, and we usually do this at night because, in the daytime, we generally remain busy with other things, like school, office, other work, running errands, and stuff like that. We all think that because we do a lot of work in the daytime, the nighttime is, in a way, free time for us to do as we want. However, this is not the right way to go about life.

We need to get enough sleep because, without it, our blood vessels and heart and other organs as such will stop healing by themselves. Without adequate sleep daily, our minds will always be occupied by one thing or another, especially about how tired we all may feel, and how we want to sleep. Sadly, many us don’t even realise this, and go about their day without sleeping much without knowing how it can affect them in the long run.

Risks for all kinds of health issues, including physical and mental health go up manifold without getting a good night’s sleep every day. Depression, anxiety, stress disorders, sleep disorders, heart attacks, diabetes, obesity, etc. are just a few of the dangers that come from not sleeping well at night.

How Should I Get More Sleep?

Good sleep does not necessarily mean that you get your 8 hours a night of sleep, which is enough. No, that is not enough – it also matters that the quality of this sleep is good. If you go to sleep with your mind disturbed, you will have disturbed sleeping – maybe you will have trouble falling off to sleep in the first place, or even keep on waking up at night because of nightmares and similar things.

The best ways to get some great sleep at night would be to turn off your phone early, maybe at 10 pm or 11 pm, and only turn it back on when you wake up in the morning, possibly at 7 am to 8 am. This is the best way to get more sleep.

• Picture Dictionary
• English Speech
• English Slogans
• English Letter Writing
• English Essay Writing
• English Textbook Answers
• Types of Certificates
• ICSE Solutions
• Selina ICSE Solutions
• ML Aggarwal Solutions
• HSSLive Plus One
• HSSLive Plus Two
• Kerala SSLC
• Distance Education

Essay on Importance of Sleep

Students are often asked to write an essay on Importance of Sleep in their schools and colleges. And if you’re also looking for the same, we have created 100-word, 250-word, and 500-word essays on the topic.

Let’s take a look…

100 Words Essay on Importance of Sleep

Understanding sleep.

Sleep is a crucial part of our lives. It helps us rest, rejuvenate, and prepare for the next day. Without sleep, our bodies and minds cannot function properly.

Why is Sleep Important?

Sleep contributes to our overall health. It allows our brain to process information and memories. It also gives our body time to repair and grow.

Effects of Lack of Sleep

Lack of sleep can lead to health issues like heart disease and obesity. It also affects our mood, making us feel irritable and stressed.

So, quality sleep is essential for our well-being. Make sleep a priority to stay healthy and happy.

250 Words Essay on Importance of Sleep

The necessity of sleep, role in physical health.

Sleep plays a significant role in the body’s healing and repair processes, particularly for the heart and blood vessels. Chronic sleep deficiency is linked to heart disease, kidney disease, high blood pressure, diabetes, and stroke. Furthermore, it aids in maintaining a healthy balance of hormones that regulate feelings of hunger and satiety, thereby indirectly influencing our body weight and food choices.

Cognitive Function and Emotional Well-being

Sleep is vital for various aspects of brain function. This includes cognition, concentration, productivity, and performance. During sleep, your brain forms new pathways to help you learn and remember information. A good night’s sleep improves problem-solving skills and enhances memory. Lack of sleep impairs these functions, leading to decreased productivity and increased mistakes.

The Impact on Mental Health

Sleep deficiency has been linked to an increased risk of developing mental health disorders, including depression, anxiety, and mood swings. Sleep helps reset our emotional brain circuits, allowing us to manage daily stress and adapt to change.

In conclusion, sleep is not a luxury, but a necessity. It’s a vital part of our lives that impacts our physical health, cognitive function, emotional well-being, and overall quality of life. Recognizing the importance of sleep and making necessary adjustments to prioritize it is a crucial step towards improved health and productivity.

500 Words Essay on Importance of Sleep

The importance of sleep: an underrated aspect of health.

Sleep, often overlooked, is a crucial aspect of our overall health and well-being. In our fast-paced society, sleep is frequently sacrificed for more seemingly productive activities, however, this neglect can have serious health consequences.

The Science of Sleep

The health implications of sleep deprivation.

Chronic sleep deprivation can lead to a host of health problems. Physically, it can increase the risk of conditions such as obesity, diabetes, and cardiovascular disease. It weakens the immune system, making one more susceptible to infections. Neurologically, lack of sleep can impair cognition, memory, and mood. Studies have shown that sleep deprivation can lead to decreased concentration, memory lapses, loss of creativity, and mood swings. Furthermore, chronic sleep deprivation has been linked to mental health disorders such as depression and anxiety.

Sleep and Academic Performance

For college students, sleep is especially important. Numerous studies have demonstrated a correlation between sleep and academic performance. Adequate sleep can enhance learning and memory, improve concentration, and boost creativity, all of which are crucial for academic success. Conversely, sleep deprivation can impede these cognitive functions, leading to decreased academic performance.

Improving Sleep Quality

In conclusion, sleep is a crucial aspect of health that is often undervalued. The implications of sleep deprivation are far-reaching, affecting physical health, mental health, and cognitive functions. As college students, it is essential to prioritize sleep to maintain overall health and optimize academic performance. By understanding the importance of sleep and adopting good sleep hygiene practices, we can reap the benefits of this vital physiological process.

That’s it! I hope the essay helped you.

Happy studying!

Leave a Reply Cancel reply

Your email address will not be published. Required fields are marked *

4.2 Sleep and Why We Sleep

Learning objectives.

By the end of this section, you will be able to:

• Describe areas of the brain involved in sleep
• Understand hormone secretions associated with sleep
• Describe several theories aimed at explaining the function of sleep
• Name and describe three theories about why we dream

We spend approximately one-third of our lives sleeping. Given the average life expectancy for U.S. citizens falls between 73 and 79 years old (Singh & Siahpush, 2006), we can expect to spend approximately 25 years of our lives sleeping. Some animals never sleep (e.g., some fish and amphibian species); other animals sleep very little without apparent negative consequences (e.g., giraffes); yet some animals (e.g., rats) die after two weeks of sleep deprivation (Siegel, 2008). Why do we devote so much time to sleeping? Is it absolutely essential that we sleep? This section will consider these questions and explore various explanations for why we sleep.

What is Sleep?

You have read that sleep is distinguished by low levels of physical activity and reduced sensory awareness. As discussed by Siegel (2008), a definition of sleep must also include mention of the interplay of the circadian and homeostatic mechanisms that regulate sleep. Homeostatic regulation of sleep is evidenced by sleep rebound following sleep deprivation. Sleep rebound refers to the fact that a sleep-deprived individual will fall asleep more quickly during subsequent opportunities for sleep. Sleep is characterized by certain patterns of activity of the brain that can be visualized using electroencephalography (EEG), and different phases of sleep can be differentiated using EEG as well.

Sleep-wake cycles seem to be controlled by multiple brain areas acting in conjunction with one another. Some of these areas include the thalamus, the hypothalamus, and the pons. As already mentioned, the hypothalamus contains the SCN—the biological clock of the body—in addition to other nuclei that, in conjunction with the thalamus, regulate slow-wave sleep. The pons is important for regulating rapid eye movement (REM) sleep (National Institutes of Health, n.d.).

Sleep is also associated with the secretion and regulation of a number of hormones from several endocrine glands including: melatonin, follicle stimulating hormone (FSH), luteinizing hormone (LH), and growth hormone (National Institutes of Health, n.d.). You have read that the pineal gland releases melatonin during sleep ( Figure 4.6 ). Melatonin is thought to be involved in the regulation of various biological rhythms and the immune system (Hardeland et al., 2006). During sleep, the pituitary gland secretes both FSH and LH which are important in regulating the reproductive system (Christensen et al., 2012; Sofikitis et al., 2008). The pituitary gland also secretes growth hormone, during sleep, which plays a role in physical growth and maturation as well as other metabolic processes (Bartke, Sun, & Longo, 2013).

Why Do We Sleep?

Given the central role that sleep plays in our lives and the number of adverse consequences that have been associated with sleep deprivation, one would think that we would have a clear understanding of why it is that we sleep. Unfortunately, this is not the case; however, several hypotheses have been proposed to explain the function of sleep.

Adaptive Function of Sleep

One popular hypothesis of sleep incorporates the perspective of evolutionary psychology. Evolutionary psychology is a discipline that studies how universal patterns of behavior and cognitive processes have evolved over time as a result of natural selection . Variations and adaptations in cognition and behavior make individuals more or less successful in reproducing and passing their genes to their offspring. One hypothesis from this perspective might argue that sleep is essential to restore resources that are expended during the day. Just as bears hibernate in the winter when resources are scarce, perhaps people sleep at night to reduce their energy expenditures. While this is an intuitive explanation of sleep, there is little research that supports this explanation. In fact, it has been suggested that there is no reason to think that energetic demands could not be addressed with periods of rest and inactivity (Frank, 2006; Rial et al., 2007), and some research has actually found a negative correlation between energetic demands and the amount of time spent sleeping (Capellini, Barton, McNamara, Preston, & Nunn, 2008).

Another evolutionary hypothesis of sleep holds that our sleep patterns evolved as an adaptive response to predatory risks, which increase in darkness. Thus we sleep in safe areas to reduce the chance of harm. Again, this is an intuitive and appealing explanation for why we sleep. Perhaps our ancestors spent extended periods of time asleep to reduce attention to themselves from potential predators. Comparative research indicates, however, that the relationship that exists between predatory risk and sleep is very complex and equivocal. Some research suggests that species that face higher predatory risks sleep fewer hours than other species (Capellini et al., 2008), while other researchers suggest there is no relationship between the amount of time a given species spends in deep sleep and its predation risk (Lesku, Roth, Amlaner, & Lima, 2006).

It is quite possible that sleep serves no single universally adaptive function, and different species have evolved different patterns of sleep in response to their unique evolutionary pressures. While we have discussed the negative outcomes associated with sleep deprivation, it should be pointed out that there are many benefits that are associated with adequate amounts of sleep. A few such benefits listed by the National Sleep Foundation (n.d.) include maintaining health, lowering stress levels, improving mood, and increasing motor coordination, as well as a number of benefits related to cognition and memory formation.

Cognitive Function of Sleep

Another theory regarding why we sleep involves sleep’s importance for cognitive function and memory formation (Rattenborg, Lesku, Martinez-Gonzalez, & Lima, 2007). Indeed, we know sleep deprivation results in disruptions in cognition and memory deficits (Brown, 2012), leading to impairments in our abilities to maintain attention, make decisions, and recall long-term memories. Moreover, these impairments become more severe as the amount of sleep deprivation increases (Alhola & Polo-Kantola, 2007). Furthermore, slow-wave sleep after learning a new task can improve resultant performance on that task (Huber, Ghilardi, Massimini, & Tononi, 2004) and seems essential for effective memory formation (Stickgold, 2005). Understanding the impact of sleep on cognitive function should help you understand that cramming all night for a test may not be effective and can even prove counterproductive.

Link to Learning

Watch this brief video that gives sleep tips for college students to learn more.

Getting the optimal amount of sleep has also been associated with other cognitive benefits. Research indicates that included among these possible benefits are increased capacities for creative thinking (Cai, Mednick, Harrison, Kanady, & Mednick, 2009; Wagner, Gais, Haider, Verleger, & Born, 2004), language learning (Fenn, Nusbaum, & Margoliash, 2003; Gómez, Bootzin, & Nadel, 2006), and inferential judgments (Ellenbogen, Hu, Payne, Titone, & Walker, 2007). It is possible that even the processing of emotional information is influenced by certain aspects of sleep (Walker, 2009).

Watch this brief video about the relationship between sleep and memory to learn more.

As an Amazon Associate we earn from qualifying purchases.

This book may not be used in the training of large language models or otherwise be ingested into large language models or generative AI offerings without OpenStax's permission.

Want to cite, share, or modify this book? This book uses the Creative Commons Attribution License and you must attribute OpenStax.

Access for free at https://openstax.org/books/psychology-2e/pages/1-introduction

• Authors: Rose M. Spielman, William J. Jenkins, Marilyn D. Lovett
• Publisher/website: OpenStax
• Book title: Psychology 2e
• Publication date: Apr 22, 2020
• Location: Houston, Texas
• Book URL: https://openstax.org/books/psychology-2e/pages/1-introduction
• Section URL: https://openstax.org/books/psychology-2e/pages/4-2-sleep-and-why-we-sleep

© Jan 6, 2024 OpenStax. Textbook content produced by OpenStax is licensed under a Creative Commons Attribution License . The OpenStax name, OpenStax logo, OpenStax book covers, OpenStax CNX name, and OpenStax CNX logo are not subject to the Creative Commons license and may not be reproduced without the prior and express written consent of Rice University.

Brain Basics: Understanding Sleep

Sleep is an important part of your daily routine—you spend about one-third of your time doing it. Quality sleep – and getting enough of it at the right times -- is as essential to survival as food and water. Without sleep you can’t form or maintain the pathways in your brain that let you learn and create new memories, and it’s harder to concentrate and respond quickly.

Sleep is important to a number of brain functions, including how nerve cells (neurons) communicate with each other. In fact, your brain and body stay remarkably active while you sleep. Recent findings suggest that sleep plays a housekeeping role that removes toxins in your brain that build up while you are awake.

Everyone needs sleep, but its biological purpose remains a mystery. Sleep affects almost every type of tissue and system in the body – from the brain, heart, and lungs to metabolism, immune function, mood, and disease resistance. Research shows that a chronic lack of sleep, or getting poor quality sleep, increases the risk of disorders including high blood pressure, cardiovascular disease, diabetes, depression, and obesity.

Sleep is a complex and dynamic process that affects how you function in ways scientists are now beginning to understand. This booklet describes how your need for sleep is regulated and what happens in the brain during sleep.

Anatomy of Sleep

Several structures within the brain are involved with sleep.

The hypothalamus , a peanut-sized structure deep inside the brain, contains groups of nerve cells that act as control centers affecting sleep and arousal.  Within the hypothalamus is the suprachiasmatic nucleus (SCN) – clusters of thousands of cells that receive information about light exposure directly from the eyes and control your behavioral rhythm.  Some people with damage to the SCN sleep erratically throughout the day because they are not able to match their circadian rhythms with the light-dark cycle.  Most blind people maintain some ability to sense light and are able to modify their sleep/wake cycle.

The brain stem , at the base of the brain, communicates with the hypothalamus to control the transitions between wake and sleep.  (The brain stem includes structures called the pons, medulla, and midbrain.)  Sleep-promoting cells within the hypothalamus and the brain stem produce a brain chemical called GABA , which acts to reduce the activity of arousal centers in the hypothalamus and the brain stem.  The brain stem (especially the pons and medulla) also plays a special role in REM sleep; it sends signals to relax muscles essential for body posture and limb movements, so that we don’t act out our dreams.

The thalamus acts as a relay for information from the senses to the cerebral cortex (the covering of the brain that interprets and processes information from short- to long-term memory).  During most stages of sleep, the thalamus becomes quiet, letting you tune out the external world.  But during REM sleep, the thalamus is active, sending the cortex images, sounds, and other sensations that fill our dreams. 

The pineal gland , located within the brain’s two hemispheres, receives signals from the SCN and increases production of the hormone melatonin , which helps put you to sleep once the lights go down.  People who have lost their sight and cannot coordinate their natural wake-sleep cycle using natural light can stabilize their sleep patterns by taking small amounts of melatonin at the same time each day.  Scientists believe that peaks and valleys of melatonin over time are important for matching the body’s circadian rhythm to the external cycle of light and darkness.

The basal forebrain , near the front and bottom of the brain, also promotes sleep and wakefulness, while part of the midbrain acts as an arousal system.  Release of adenosine (a chemical by-product of cellular energy consumption) from cells in the basal forebrain and probably other regions supports your sleep drive.  Caffeine counteracts sleepiness by blocking the actions of adenosine.

The amygdala , an almond-shaped structure involved in processing emotions, becomes increasingly active during REM sleep. 

Sleep Stages and Mechanisms

Sleep stages.

There are two basic types of sleep:  rapid eye movement (REM) sleep and non-REM sleep (which has three different stages).  Each is linked to specific brain waves and neuronal activity.  You cycle through all stages of non-REM and REM sleep several times during a typical night, with increasingly longer, deeper REM periods occurring toward morning. 

Stage 1 non-REM sleep is the changeover from wakefulness to sleep.  During this short period (lasting several minutes) of relatively light sleep, your heartbeat, breathing, and eye movements slow, and your muscles relax with occasional twitches.  Your brain waves begin to slow from their daytime wakefulness patterns.  

Stage 2 non-REM sleep is a period of light sleep before you enter deeper sleep.  Your heartbeat and breathing slow, and muscles relax even further.  Your body temperature drops and eye movements stop.  Brain wave activity slows but is marked by brief bursts of electrical activity.  You spend more of your repeated sleep cycles in stage 2 sleep than in other sleep stages.

Stage 3 non-REM sleep is the period of deep sleep that you need to feel refreshed in the morning.  It occurs in longer periods during the first half of the night.  Your heartbeat and breathing slow to their lowest levels during sleep.  Your muscles are relaxed and it may be difficult to awaken you.  Brain waves become even slower.  

REM sleep first occurs about 90 minutes after falling asleep.  Your eyes move rapidly from side to side behind closed eyelids.  Mixed frequency brain wave activity becomes closer to that seen in wakefulness.  Your breathing becomes faster and irregular, and your heart rate and blood pressure increase to near waking levels.  Most of your dreaming occurs during REM sleep, although some can also occur in non-REM sleep.  Your arm and leg muscles become temporarily paralyzed, which prevents you from acting out your dreams.  As you age, you sleep less of your time in REM sleep.  Memory consolidation most likely requires both non-REM and REM sleep.

Sleep Mechanisms

Two internal biological mechanisms –circadian rhythm and homeostasis–work together to regulate when you are awake and sleep.  

Circadian rhythms direct a wide variety of functions from daily fluctuations in wakefulness to body temperature, metabolism, and the release of hormones.  They control your timing of sleep and cause you to be sleepy at night and your tendency to wake in the morning without an alarm.  Your body’s biological clock, which is based on a roughly 24-hour day, controls most circadian rhythms.  Circadian rhythms synchronize with environmental cues (light, temperature) about the actual time of day, but they continue even in the absence of cues. 

Sleep-wake homeostasis keeps track of your need for sleep.  The homeostatic sleep drive reminds the body to sleep after a certain time and regulates sleep intensity.  This sleep drive gets stronger every hour you are awake and causes you to sleep longer and more deeply after a period of sleep deprivation.

Factors that influence your sleep-wake needs include medical conditions, medications, stress, sleep environment, and what you eat and drink.  Perhaps the greatest influence is the exposure to light.  Specialized cells in the retinas of your eyes process light and tell the brain whether it is day or night and can advance or delay our sleep-wake cycle.  Exposure to light can make it difficult to fall asleep and return to sleep when awakened.

Night shift workers often have trouble falling asleep when they go to bed, and also have trouble staying awake at work because their natural circadian rhythm and sleep-wake cycle is disrupted.  In the case of jet lag, circadian rhythms become out of sync with the time of day when people fly to a different time zone, creating a mismatch between their internal clock and the actual clock. 

How Much Sleep Do You Need?

Your need for sleep and your sleep patterns change as you age, but this varies significantly across individuals of the same age.  There is no magic “number of sleep hours” that works for everybody of the same age.  Babies initially sleep as much as 16 to 18 hours per day, which may boost growth and development (especially of the brain).  School-age children and teens on average need about 9.5 hours of sleep per night.  Most adults need 7-9 hours of sleep a night, but after age 60, nighttime sleep tends to be shorter, lighter, and interrupted by multiple awakenings.  Older people are also more likely to take medications that interfere with sleep. 

In general, people are getting less sleep than they need due to longer work hours and the availability of round-the-clock entertainment and other activities. 

Many people feel they can "catch up" on missed sleep during the weekend but, depending on how sleep-deprived they are, sleeping longer on the weekends may not be adequate.

Dreaming and Sleep Tracking

Everyone dreams.  You spend about 2 hours each night dreaming but may not remember most of your dreams.  Its exact purpose isn’t known, but dreaming may help you process your emotions.  Events from the day often invade your thoughts during sleep, and people suffering from stress or anxiety are more likely to have frightening dreams.  Dreams can be experienced in all stages of sleep but usually are most vivid in REM sleep.  Some people dream in color, while others only recall dreams in black and white.

Tracking Sleep Through Smart Technology

Millions of people are using smartphone apps, bedside monitors, and wearable items (including bracelets, smart watches, and headbands) to informally collect and analyze data about their sleep.  Smart technology can record sounds and movement during sleep, journal hours slept, and monitor heart beat and respiration.  Using a companion app, data from some devices can be synced to a smartphone or tablet, or uploaded to a PC.  Other apps and devices make white noise, produce light that stimulates melatonin production, and use gentle vibrations to help us sleep and wake.

The Role of Genes and Neurotransmitters

Chemical signals to sleep      .

Clusters of sleep-promoting neurons in many parts of the brain become more active as we get ready for bed.  Nerve-signaling chemicals called neurotransmitters can “switch off” or dampen the activity of cells that signal arousal or relaxation.  GABA is associated with sleep, muscle relaxation, and sedation.  Norepinephrine and orexin (also called hypocretin) keep some parts of the brain active while we are awake.  Other neurotransmitters that shape sleep and wakefulness include acetylcholine, histamine, adrenaline, cortisol, and serotonin.

Genes and sleep

Genes may play a significant role in how much sleep we need.  Scientists have identified several genes involved with sleep and sleep disorders, including genes that control the excitability of neurons, and "clock" genes such as Per , tim , and Cry that influence our circadian rhythms and the timing of sleep.  Genome-wide association studies have identified sites on various chromosomes that increase our susceptibility to sleep disorders.  Also, different genes have been identified with such sleep disorders as familial advanced sleep-phase disorder, narcolepsy, and restless legs syndrome.  Some of the genes expressed in the cerebral cortex and other brain areas change their level of expression between sleep and wake.  Several genetic models–including the worm, fruit fly, and zebrafish–are helping scientists to identify molecular mechanisms and genetic variants involved in normal sleep and sleep disorders.  Additional research will provide better understand of inherited sleep patterns and risks of circadian and sleep disorders. 

Sleep studies

Your health care provider may recommend a polysomnogram or other test to diagnose a sleep disorder.  A polysomnogram typically involves spending the night at a sleep lab or sleep center.  It records your breathing, oxygen levels, eye and limb movements, heart rate, and brain waves throughout the night.  Your sleep is also video and audio recorded.  The data can help a sleep specialist determine if you are reaching and proceeding properly through the various sleep stages.  Results may be used to develop a treatment plan or determine if further tests are needed.

Tips for Getting a Good Night's Sleep

Getting enough sleep is good for your health.  Here are a few tips to improve your sleep:

• Set a schedule – go to bed and wake up at the same time each day.
• Exercise 20 to 30 minutes a day but no later than a few hours before going to bed.
• Avoid caffeine and nicotine late in the day and alcoholic drinks before bed.
• Relax before bed – try a warm bath, reading, or another relaxing routine.
• Create a room for sleep – avoid bright lights and loud sounds, keep the room at a comfortable temperature, and don’t watch TV or have a computer in your bedroom.
• Don’t lie in bed awake.  If you can’t get to sleep, do something else, like reading or listening to music, until you feel tired. 
• See a doctor if you have a problem sleeping or if you feel unusually tired during the day.  Most sleep disorders can be treated effectively.

Hope Through Research

Scientists continue to learn about the function and regulation of sleep.  A key focus of research is to understand the risks involved with being chronically sleep deprived and the relationship between sleep and disease.  People who are chronically sleep deprived are more likely to be overweight, have strokes and cardiovascular disease, infections, and certain types of cancer than those who get enough sleep.  Sleep disturbances are common among people with age-related neurological disorders such as Alzheimer’s disease and Parkinson’s disease.  Many mysteries remain about the association between sleep and these health problems.  Does the lack of sleep lead to certain disorders, or do certain diseases cause a lack of sleep?  These, and many other questions about sleep, represent the frontier of sleep research.

• Career Advice

Just Go to Bed

By  Nate Kreuter

You have / 5 articles left. Sign up for a free account or log in.

I’m more or less perpetually awed by how poorly we academics take care of ourselves much of the time. Sometimes I think that, almost by definition, the typical scholar-teacher is a neurotic who routinely puts work before his or her own health. Unnecessarily. Perhaps this is why I frequently find myself writing about self-care issues, because I’m worried about the ways in which many of us routinely neglect our own physical, mental, and emotional health. Obviously enough, ours isn’t the only line of work in which people give their careers precedence over health and comfort, but I do think that it’s a common problem in our profession. Credit it to selflessness if you like — caring about students, intellectual inquiry, the institutions we serve — but putting one’s career before one’s health is not a winning lifestyle over the long term. I recently had to re-address one of my own health-neglecting tendencies. I had to become a lot more conscientious about my sleep, and in particular about getting enough hours of quality sleep to, well, function. In my usual beginning of the semester effort to avoid falling behind, and in an attempt to fulfill all of the ambitious promises I made to myself after the fall semester (a predictable cycle for me), my work began to cut into my sleep. I normally get and can function well on about 6 hours of sleep, assuming that about twice a week, but not necessarily on weekends, I get a good, solid 8 hours. About once a month I might go on a 10-hour sleep bender. But in the beginning of the semester rush, I began to fatigue early in the evening, earlier than usual anyway, and it took me about a week to realize why, even though the reason was obvious. I had been clipping my 6 hour nights down to about 5, and sometimes 4. And my "long" nights were only about 6-7 hours. The effect was creeping and cumulative. After about 4 weeks of this reduced-sleep routine, which I had embarked on without ever intending to, I began to crash. It caught up with me, in a big way. I couldn’t focus on my work, I was fatiguing earlier in the day, and I was definitely more irritable than usual. Failing to exercise regularly has the same effects on me, but I had been keeping up with my workouts. During every major phase of my adult life — college, my first job after college, graduate school, and now as a junior faculty member — I have had to relearn the simple fact that there is a point of diminishing returns when it comes to burning the midnight oil. Especially when it comes to cognitively demanding tasks, I can get more done in one well-rested hour than I can in three sleep-deprived hours. The solution is simple, but sometimes difficult to allow ourselves: get more sleep. Napping, if your professional and family life can accommodate it, is one way to make up for sleep deprivation. I myself am not an accomplished napper. It takes me too long to fall asleep. In my own friend group, the best nappers I know were all in the military. I had a college friend who was in the National Guard and who could, in a living room full of rowdy guys playing videos games, simply decide to go to sleep. It was as if all he had to do was throw a switch and he would be out for an hour, falling asleep immediately, waking almost precisely an hour later, with nary a grain of sand in his eye, refreshed and recharged. I envied him this talent, and still do. Another friend of mine works two jobs, one from about 5 in the morning until noon, and the other from 4 in the afternoon until 9 at night. He never seems tired, in part because he takes a nap just about every day in between his two different jobs. Allowing yourself a night of extended sleep after several too-short nights, while less ideal than getting regular, reliable amounts of sleep, can also help make up for the deficits. When the semester is at its worst, I have to actually schedule sleep, as a way of conscientiously compelling myself not to over-schedule and set aside the time that my brain needs to recharge. I’m no expert on the science on circadian rhythms, but I know that mine have changed as I’ve aged. During college I was most productive in the late evening. I could hang out with friends and then return to my room, refocus on my work, and work until a large task was completed. Things have completely shifted. Now if I have important or cognitively demanding work to get done -- and I do all the time -- it’s better for me to turn in early and get up early as well, addressing my hardest work before the routine demands of the day interrupt my ability to concentrate. If I don’t write in the morning, I probably won’t get a chance to write all day. And the writing I do in the early morning is almost always better writing than the writing I do at other times. Managing my sleep has required that I protect my morning writing time, which basically means going to bed early instead of sleeping in. I simultaneously love sleep and resent it. I love it because it feels so good. But I resent it because of how much time it takes from other things. I might wake up one morning and think to myself, “Wow, what a great night’s sleep. I feel really good.” But in a month I won’t remember that particular evening’s sleep. What I will remember in a month is the great bike ride that I took in my waking hours, or a particularly excellent class discussion. The point is that we all require different amounts of sleep, within a range, to function at our best, but as overworking educators many of are inclined to cut our sleep time before anything else. That bill comes due eventually. I imagine that many readers are thinking to themselves things like, "This jerk obviously doesn’t have kids," or, "6 hours of sleep, I’d kill for 6 hours of sleep." I know, I know. This is easy advice to give, and it probably does a poor job of accounting for the demands of your particular life. But I stand by my point. You have 6 hours of grading to finish? Well, maybe it you get a couple extra hours of sleep tonight your 6 hours of grading will, in a more mentally rested state, really only be 4 or 5 hours of grading. Maybe even less. We all need sleep.  

GOP Platform: ‘Make Our College Campuses Safe and Patriotic Again’

Share this article, more from career advice.

Hiring for Humanity

To create an office culture marked by trust, humanity and collaboration, Diana Lawrence poses a rather unexpected que

In Praise of Lunch

Amid the stress and clutter of our daily lives, and the divisions straining our politics and culture, we need sustain

Bad-Faith Counteroffers

Black and other minoritized faculty don’t receive equitable ones if they receive them at all, which harms both them a

• Become a Member
• Sign up for Newsletters
• Learning & Assessment
• Diversity & Equity
• Career Development
• Labor & Unionization
• Shared Governance
• Academic Freedom
• Books & Publishing
• Financial Aid
• Residential Life
• Free Speech
• Physical & Mental Health
• Race & Ethnicity
• Sex & Gender
• Socioeconomics
• Traditional-Age
• Adult & Post-Traditional
• Teaching & Learning
• Artificial Intelligence
• Digital Publishing
• Data Analytics
• Administrative Tech
• Alternative Credentials
• Financial Health
• Cost-Cutting
• Revenue Strategies
• Academic Programs
• Physical Campuses
• Mergers & Collaboration
• Fundraising
• Research Universities
• Regional Public Universities
• Community Colleges
• Private Nonprofit Colleges
• Minority-Serving Institutions
• Religious Colleges
• Women's Colleges
• Specialized Colleges
• For-Profit Colleges
• Executive Leadership
• Trustees & Regents
• State Oversight
• Accreditation
• Politics & Elections
• Supreme Court
• Student Aid Policy
• Science & Research Policy
• State Policy
• Colleges & Localities
• Employee Satisfaction
• Remote & Flexible Work
• Staff Issues
• Study Abroad
• International Students in U.S.
• U.S. Colleges in the World
• Intellectual Affairs
• Seeking a Faculty Job
• Advancing in the Faculty
• Seeking an Administrative Job
• Advancing as an Administrator
• Beyond Transfer
• Call to Action
• Confessions of a Community College Dean
• Higher Ed Gamma
• Higher Ed Policy
• Just Explain It to Me!
• Just Visiting
• Law, Policy—and IT?
• Leadership & StratEDgy
• Leadership in Higher Education
• Learning Innovation
• Online: Trending Now
• Resident Scholar
• University of Venus
• Student Voice
• Academic Life
• Health & Wellness
• The College Experience
• Life After College
• Academic Minute
• Weekly Wisdom
• Reports & Data
• Quick Takes
• Advertising & Marketing
• Consulting Services
• Data & Insights
• Hiring & Jobs
• Event Partnerships

4 /5 Articles remaining this month.

Sign up for a free account or log in.

• Sign Up, It’s FREE

127 Sleep Essay Topics and Essay Examples

🏆 best sleep topic ideas & essay examples, 👍 good sleep topics to write about, 💡 interesting sleep topics, ❓ research questions about sleep.

• Problem of Sleep Deprivation This is due to disruption of the sleep cycle. Based on the negative effects of sleep deprivation, there is need to manage this disorder among Americans.
• The Role of Sleep in Humans’ Well-Being Each of the speakers in the videos focuses on a different characteristic of sleep, but all of them agree that without enough sleep, one does not perform to the fullest potential.
• Sleepwalking Through Life In this case, there is a large context of life that people can be part of which should be understood. All in all, there is a lot that can be done to ensure that people […]
• Effects of Lullaby Music on Quality of Sleep in Adults With Insomnia Insomnia consists of deprivation of the duration and quality of sleep, which affects the psychological and physical condition of people. In addition, the main limitation may be the unreliability of the information provided by the […]
• Sleeping Habits & Physical Health: Students’ Perception Using the survey as the data collection tool, the investigators state that most students do not have appropriate sleep habits, although they agree that their academic success and physical health suffer because of the lack […]
• The Effect of Sleep Quality and IQ on Memory Therefore, the major aim of sleep is to balance the energies in the body. However, the nature of the activity that an individual is exposed to determines the rate of memory capture.
• Cross-Cultural Sleeping Arrangements in Children The aim of this paper is to study the different sleep patterns such as solitary or co sleeping in the United States of America and different cultures around the world.
• Blue Light Effect on Human Sleep The introduction is comprised of a thesis statement and a description of the critical thoughts of the paper. At the end of the paper, recommendations on how to reduce the adversarial effect of the blue […]
• Effects of Sleeping Disorders on Human On the other hand, Dyssomnia relates to sleep disorders that develop as a result of lack of adequate sleep. In some cases, antidepressants have been used to cure sleep disorders that are as a result […]
• The Importance of Sleeping and Dreaming Finally, I would not take this pill since I love seeing dreams and realize that this “miracle medicine” will cause too many negative consequences.
• How the Modern Life Has Affected Sleep Czeisler mentioned in the DW documentary about sleep: “The electric light to which we are exposed in terms of resetting our internal clock is like light on steroids”. That is why we should affect the […]
• Sleep-Disordered Breathing and Acute Ischemic Stroke In this case study, the investigator focused on ischemic stroke, one of the most common types of stroke in the world.
• The Biological Basis of Sleep The authors suggest that it needs more accurate measurement of sleep and wake pattern by the use of the electrooculogram, the recording of the movement of the eye, EEG and electromyogram, the recording of the […]
• Psychology of Sleep: Article Study The field of sleep and sleep disorders has been an integral part of psychological investigations: a number of scientists find it necessary to contribute sleep education and offer the ideas which help people improve their […]
• Sleep Stages and Disorders A more elaborate look into understanding sleep take a look at the two aspects of sleep which is the behavior observed during sleeping periods as well as the scientific explanation of the physiological processes involved […]
• Sleep and Sensory Reactivity in the School-Aged Children The interaction of these elements should be considered in therapies expressly designed to improve sleep disruptions or sensory processing difficulties in children as a possible negative determinant that may adversely affect children’s health and normal […]
• Stages of Sleep, Brain Waves, and the Neural Mechanisms of Sleep As sleep is extremely important for a person’s well-being, I believe it is essential to pay attention to the mechanisms of sleep and how they work.
• The Issue of Chronic Sleep Deprivation The quality of sleep significantly impacts the health and performance of the human body. These findings point to significant promise for the use of exercise in the treatment of sleep disorders, but a broader body […]
• Sleep-Wake, Eating, and Personality Disorders Treatment On the other hand, treatment with prazosin and mianserin was effective; for example, the drug mianserin benefits patients suffering from sleep disorders. Psychotherapy approaches like Cognitive Behavioural Therapy for Insomnia and Imaginary Rehearsal Therapy are […]
• Sleep and Meditation Can Predict an Individual’s Satisfaction With Life This aim of this study is to investigate the effects of quality sleep and mindfulness on life satisfaction. In a nutshell, life satisfaction depends on the quality of sleep and meditation.
• Water Consumption and Sleep Hygiene Practices First, I will discuss that safe and sufficient water facilitates the practice of hygiene and well-being and is a critical determining factor for health.
• Depression Associated With Sleep Disorders Y, Chang, C. Consequently, it directly affects the manifestation of obstructive sleep apnea, restless leg syndrome, and periodic limb movement disorder in people with depression.
• How Technology Affects Sleep in Adolescents The critique will focus on the various sections of the article, where the strengths and weaknesses of each are outlined and discussed. The title of the article excellently reflects the essence of the research.
• Sleep Disturbance in Children Any disorder that alters the craniofacial or pharyngeal anatomy predisposes the child to obstructive narcolepsy is considered a medical problem associated with sleep disturbances in children. Central Sleep Apnea is the repeated cessation or decrease […]
• ADHD and Problems With Sleep This is because of the activity of a person in the middle of the day and the condition around them. The downside of the study is that the study group included 52 adults with ADHD […]
• Solving the Sleep Problem through TQM Principles The initiative to address the lack of sleep among employees and consequently improve their performance and the quality of services requires teamwork optimization.
• Eat, Sleep, and Console: Narcotic Abstinence Syndrome in Infants The choice of the quantitative design is justified by the necessity to prove the superiority of the proposed solution to the one that is currently deployed as the alternative way of managing the needs of […]
• Hippocampus-Dependent Memories During Sleep The smell was chosen because it was not necessary to interrupt the integrity of the subjects’ sleep to introduce it into the experiment.
• The Influence of Sleep Deprivation on Human Body It contradicts living in harmony with God, as when the person is irritated and moody, it is more difficult to be virtuous and to be a source of joy for others.
• Programs in Family Sleep Institute She explained to me the sleep cycle of the child and the adult, how many hours my child is supposed to sleep, the bedtime routine, and the method that we had to adopt during the […]
• Sleep Deprivation and Insomnia: Study Sources The topic of this audio record is a variety of problems with sleep and their impact on an organism. They proved the aforementioned conclusion and also paid attention to the impact of sleep deprivation on […]
• Sleep Problems Among Student-Athletes Despite the importance of the topic under study and the conclusions reached, the work raised additional questions and had some limitations.
• Excessive Sleepiness May Be Cause of Learning, Attention, and School Problems The information in the article “Excessive Sleepiness May Be Cause of Learning, Attention, and School Problems” by Calhoun and Fernandez-Mendoza is used to show that heavy daytime sleeping may be a cause of attention, learning, […]
• Sleep Hygiene Intervention Plan for Young Adults The main goals of this plan are to develop a list of guidelines for nurses on how they can offer a kind of educational program to their patients based on which young adults can understand […]
• Neurocognitive Consequences of Sleep Deprivation The CNS consists of the brain and the spinal cord while the PNS consists of all the endings of the nerve extensions in all organs forming the web that extends throughout the entire organ.
• Sleep Apnea, the Heart and the Brain in the Elderly They should get the necessary treatment of heart diseases and neuromuscular disorders Be attentive to yourself and live a full life!
• Sleepiness Level and Degree: Research Instruments A sum ranging from 0 to 24 of the score on the eight items makes the total score of the ESS.
• Evolutionary Biology: Sleep Patterns in Mammals This synthesis addresses the question of the origin of sleep in mammals and traces this phenomenon by studying the evolution of the mammalian brain and suggesting possible external factors that affect sleep patterns.
• “Childbirth Fear and Sleep Deprivation in Pregnant Women” by Hall To further show that the information used is current, the authors have used the APA style of referencing which demand the naming of the author as well as the year of publication of the article/book […]
• African Sleeping Sickness Using the various forms of detection and diagnosis it was discovered that African sleeping sickness is a major problem in Sub-Saharan Africa.
• The Use of Sleephormone in Children With Neuro-Developmental Disorders For the better management of the data that are planned to be retrieved from the clinical trial procedures, the following list of the definitions and acronyms used in the trial process is given.
• Sleep Deprivation and Learning at University It is a widely known fact that numerous people face the problem of lack of sleep. Second, sleeping is essential for increasing the productivity of students in the context of learning.
• Communication Between Sleep, Behavior and Obesity The purpose of the study seeks to evaluate the association between nighttime media use with sleep behaviors and variation in weight status for first-semester college students.
• Obstructive Sleep Apnea and Heart Diseases In children with Down syndrome, incidence rates of hypertension and sleepiness are high, and the problem is compounded in the presence of OSA.
• Sleep is a Vital Stage of a Day Cycle in Humans During the first stage of sleep, the EEG shifts to theta waves, with a frequency of 4 7 Hz. There are numerous sleep disorders, which can affect the well-being of a person.
• “The Effect of Nursing Quality Improvement and Mobile Health Interventions on Infant Sleep Practices” by Moon The following analysis is related to the article, “The effect of nursing quality improvement and mobile health interventions on infant sleep practices” by Moon et al.
• Sleep Deprivation: Biopsychology and Health Psychology Another theory that has been proposed in relation to sleep is the Circadian theory which suggests that sleep evolved as a mechanism to fit organisms into the light dark cycle of the world.
• Study of the Sleeping Process The paper entails a comprehensive analysis of the sleeping process in addition to evaluating the factors that affect the sleeping process.
• Sleep Disorders: Sleep Deprivation of the Public Safety Officers The effects of sleep disorders and fatigue on public safety officers is a social issue that needs to be addressed with more vigor and urgency so that the key issues and factors that are salient […]
• Sleep Versus Social Demands in Students The effects of has been exhibited more greatly in animals through studies and all animals have been shown to sleep in different forms.
• Sleep Deprivation: Personal Experiment As I had been perplexed, I did not take a step of reporting the matter to the police neither did I inform my neighbors.
• Recuperative Versus Circadian Theory of Sleep The Recuperative theory of sleep is based on the premise that humans require sleep to rejuvenate and recoup spent energy during the waking period.
• Biology. Adolescent Sleep Pattern The habit of sleep is very individual specific therefore a study of the pattern of sleep of a group needs to be evaluated to get an understating of the pattern of sleep.
• Non- and Rapid Eye Movement Sleep Non REM sleep represents 75% of sleep duration and occurs in four stages and REM sleep represents stage 5 of sleep.
• Main Information about Sleeping Disorders In the introduction part the paper provides an overview of sleep and sleep disorders. This led to the conclusion that instead of being a quite and peaceful period of rest and resuscitation as everyone would […]
• Memory Consolidation and Reconsolidation After Sleep The memory consolidation of the visual skill tasks is related to the REM sleep and the short wave component of the NREM.
• Sleep Disorders: Narcolepsy, Obstructive Sleep Apnea, Insomnia An important aspect of the pathogenesis is the autoimmune lesion of the orexin neurons of the hypothalamus, which leads to a decrease in the level of hypocretin-1.
• Sleep Helps to Repair Damaged DNA in Neurons The researchers found that the chromosomes in the fish’s neurons would often change shape while their owners slept, enabling the repair of the damage accumulated in periods of activity.
• Adolescent Sleep and the Impact of Technology Use Particularly, the authors of the study explain why there is the need to know the answer to the question by providing a profound background to the case and stating that innovative technology has a profound […]
• Coffee Effects on Sleeping Patterns: Experiment Consumption of coffee before going to bed will cause individuals to have difficulty falling asleep The amount of coffee the subjects drink before going to bed The time after going to bed that subjects fall […]
• Sleep Disruptions in Healthcare Professionals First of all, the sleep disruption may lead to a lack of coordination in the team because some members would be fatigued during the working hours, which would interfere with their functioning and concentration in […]
• Sleep May Be Nature’s Time Management Tool by Carey The author states that no one knows why sleep exists therefore setting the context for the article in which she advances the numerous theories that are advanced as to the role that sleep plays.
• Physical Activity and Sleep Health in Adults In the introduction to the analysed study, a substantial scientific background for the problem of improving physical activity and sleep in adults is presented.
• Insomnia and Narcolepsy: Sleeping Disorders Besides, it was established that people with insomnia are inclined to overestimate the negative effect of sleeping disorder and underestimate the total time of sleep.
• Sleep Patterns’ Impact on Academic Performance Because some university classes begin as early as 7 o’clock in the morning and finish in the evening, the only option for such students is to reduce the length of night-time sleep in order to […]
• Prevalence of Sleep Disorders among Medical Students Nightmares and dreams arise in the course of REM sleep as it is linked to desynchronized and quick brain waves, deferral of homeostasis, and failure of muscular tonus.
• Emotions Clusters and Sleep Failure Earlier critics had argued that PANAS was not suitable for children, and this led to the development of specific PANAS-C for children.
• Sleep Deprivation and Specific Emotions The purpose of this study is to develop an understanding of the relationship between sleep deprivation and emotional behaviors. The study looks to create a link between the findings of past researches on the emotional […]
• Sleep Disturbance, Depression, Anxiety Correlation The above imply that many questions are still unanswered with respect to the kinds of sleep complaints affecting undergraduates and the impact on their psychological health.
• Relationship Between Depression and Sleep Disturbance It was emphasized that persistent disturbance, its severity, and the intermittent nature of the sleep were not associated with depression and its recurrence in the following years. The sleeping disturbance is a risk factor that […]
• Sleep and Psychopathology Relationships – Psychology Generally, available evidence shows that feelings of negative emotions such as anxiety are characterized by the dysfunction in cognitive and interpersonal spheres.
• Sleep Disorder Consequences on the Immune System Consequently, the research question for this paper is: what are the consequences of sleep disorder on the immune system? The primary goal of the study is to determine the effects of sleep disorder on the […]
• Importance of Sleep – Psychology Precisely, most of the organs of the body are at rest during sleep. It is during sleep that the body encodes the information it obtains during the day into the memory.
• Dream and Sleep Cycle Dreams occur in any of the phases of sleep, nonetheless, the most concise, clear, vivid and memorable dreams are observed in the last phase of sleep (known as the rapid eye movement REM sleep.
• Changes of Sleep in the Course of One Night Furthermore, voltage generated by eye rotation in their sockets and electrical activities of the muscles all help in the study of the cycles of sleep in the course of one night.
• Sleep Deprivation Impacts on College Students Additional research in this field should involve the use of diverse categories of students to determine the effects that sleep deprivation would have on them.
• Relationship Between Sleep and Depression in Adolescence Using SPSS for data analysis, the results indicate the presence of a correlation between elements of depression and sleep duration and quality.
• Ethical Issues in Treating Obstructive Sleep Apnea with Exercise Independently The approaches should ensure that necessary preventive and curative measures are put in place to facilitate the process of eradicating the disease that is causing immense sleep related complications.
• How Sleep Deprivation Affects College Students’ Academic Performance The study seeks to confirm the position of the hypothesis that sleep deprivation leads to poor academic performance in college students.
• Insomnia: A Sleeping Disorder Type Causes of insomnia can be classified into two; factors contributing to acute insomnia and chronic insomnia. Chronic insomnia can be as a result of emotional stress.
• The Eight Hour Dilemma: Sleeping Time Reduction. When a Single Hour Makes a Difference While reducing the amount of sleeping hours to seven and less can possibly lead to sleep deprivation and the further changes for the worse in a human body, eight hours are no longer the borderline […]
• Infant Sleep Disturbance (ISD) The uniqueness of this study stems from the fact that it would provide a clear understanding of the most effective intervention/basis for physicians and parents to pursue in the management of sleep disorders among infants […]
• Underlying Issues Associated with Sleep Disorders and Stress Of fundamental importance to this research paper is the realization that the amount of sleep that an individual gets is one of the internal factors that influence his or her own capacity to handle stress.
• The Consequences of Poor Sleep Conducting a research devoted to human sleep habits in children and feeling the affect on their confidence as adults, the existing data should be evaluated and the conclusions are to be drawn in the sphere […]
• Effects of Sleep Deprivation While scientists are at a loss explaining the varying sleeping habits of different animals, they do concede that sleep is crucial and a sleeping disorder may be detrimental to the health and productivity of a […]
• The Role of Melatonin in Determining the Sleep-Wake Cycle Melatonin plays a significant role in the circadian control of sleep as well as in restraining the development of malignant cells.
• The Phantom Menace of Sleep-Deprived Doctors This is one of the problems that should be addressed by hospital administrators. Therefore, it is vital to develop strategies that can improve the work of medical institutions.
• Sleep and Dreams: How Do They Work? During sleep, the brain is at rest while the rest of the body system is in active state. Thus, to prevent most of the body disorders in human both psychiatrists and health experts recommend sleep.
• Sleep Disorders with Children and Adolescences This study is important in terms of understanding of the effectives of empirical and theoretical research in the field and attracting the scientist’s attention to the problem so that appropriate and effective treatment to be […]
• Sleep and Its Implication on Animals This paper is set to synthesize the evolution sleep in animals, its benefits and the recent knowledge that is linked to this natural phenomenon of near unconsciousness.”A Third of Life” addressed what is sleep and […]
• Sleep Process Research There are said to have five sleep stages, which are divided in to two: the rapid eye movement and the non rapid eye movement during which the dreams occur.
• A Day in the Sleep Clinic: Culture and Health The third aspect of the PEN-3 Model looks at the cultural issues and health beliefs. For instance, the Sudanese family belief in superstition may not affect the health outcome in the hands of the doctor.
• Using Depressants During Sleep Time The paper also holds up the notion that, today it is important to control the sleeping patterns, to conform to the lifestyle demands. The drugs are mainly used generally to reduce the sleep delays, thus […]
• Sleep Improves Memory It is possible to replace a traumatic memory with a pleasant one then take a brief moment of sleep to reinforce the pleasant memory.
• How Much Sleep Do You Need by Age?
• What Is an Sleep?
• What Is the Purpose of Sleep?
• What Is Good Sleep?
• Why Is Sleep Important for Health?
• What Happens if We Don’t Sleep?
• Why Is It Called Sleep?
• What Causes Lack of Sleep?
• What Age Gets the Most Sleep?
• What Is the Most Healthy Time to Wake Up?
• Why Do Older People Need Less Sleep?
• How Much Sleep Is Healthy?
• What Are Interesting Facts About Sleep?
• What Happens During Sleep?
• Why Should We Drink Water Before Sleeping?
• How to Fall Asleep Fast Within 5 Minutes?
• Which Foods Make Sleepy?
• What to Drink to Sleep Faster?
• What Are the Sleep Tricks?
• What Part of the Brain Causes Sleep?
• How Can I Get Better Sleep?
• Which Oil Helps You Sleep?
• Does Warm Milk Help You Sleep?
• How Can I Relax When I Can’t Sleep?
• At What Time Is the Body Ready for Sleep?
• Memory Research Ideas
• Mental Health Essay Ideas
• Hygiene Essay Topics
• Mind Research Ideas
• Music Therapy Ideas
• Nervous System Research Topics
• Oppression Research Topics
• Pharmacy Research Ideas
• Chicago (A-D)
• Chicago (N-B)

IvyPanda. (2024, February 29). 127 Sleep Essay Topics and Essay Examples. https://ivypanda.com/essays/topic/sleep-essay-topics/

"127 Sleep Essay Topics and Essay Examples." IvyPanda , 29 Feb. 2024, ivypanda.com/essays/topic/sleep-essay-topics/.

IvyPanda . (2024) '127 Sleep Essay Topics and Essay Examples'. 29 February.

IvyPanda . 2024. "127 Sleep Essay Topics and Essay Examples." February 29, 2024. https://ivypanda.com/essays/topic/sleep-essay-topics/.

1. IvyPanda . "127 Sleep Essay Topics and Essay Examples." February 29, 2024. https://ivypanda.com/essays/topic/sleep-essay-topics/.

Bibliography

IvyPanda . "127 Sleep Essay Topics and Essay Examples." February 29, 2024. https://ivypanda.com/essays/topic/sleep-essay-topics/.

Theses on Sleep

Summary: In this essay, I question some of the consensus beliefs about sleep, such as the need for at least 7 hours of sleep for adults, harmfulness of acute sleep deprivation, and harmfulness of long-term sleep deprivation and our inability to adapt to it.

It appears that the evidence for all of these beliefs is much weaker than sleep scientists and public health experts want us to believe. In particular, I conclude that it’s plausible that at least acute sleep deprivation is not only not harmful but beneficial in some contexts and that it’s that we are able to adapt to long-term sleep deprivation.

I also discuss the bidirectional relationship of sleep and mania/depression and the costs of unnecessary sleep, noting that sleeping 1.5 hours per day less results in gaining more than a month of wakefulness per year, every year.

Note: I sleep the normal 7-9 hours if I don’t restrict my sleep. However, stimulants like coffee, modafinil, and adderall seem to have much smaller effect on my cognition than on cognition of most people I know. My brain in general, as you might guess from reading this site , is not very normal. So, be cautious before trying anything with your sleep on the basis of the arguments I lay out below. Specifically do not make any drastic changes to your sleep schedule on the basis of reading this essay and, if you want to experiment with sleep, do it gradually (i.e. varying the average amount of sleep by no more than 30 minutes at a time) and carefully.

Also see Natália Coelho Mendonça Counter-theses on Sleep .

Comfortable modern sleep is an unnatural superstimulus. Sleepiness, just like hunger, is normal.

The default argument for sleeping 7-9 hours a night is that this is the amount of sleep most of us get “naturally” when we sleep without using alarms. In this section, I argue against this line of reasoning, using the following analogy:

• Experiencing hunger is normal and does not necessarily imply that you are not eating enough. Never being hungry means you are probably eating too much.
• Experiencing sleepiness is normal and does not necessarily imply that you are undersleeping. Never being sleepy means you are probably sleeping too much.

Most of us (myself included) eat a lot of junk food and candy if we don’t restrict ourselves. Does this mean that lots of junk food and candy is the “natural” or the “optimal” amount for health?

Obviously, no. Modern junk food and candy are unnatural superstimuli, much tastier and much more abundant than any natural food, so they end up overwhelming our brains with pleasure, especially given that we are bored at work, college, or in high school so much of the day.

What if the only food available to you was junk food and candy?

• If you don’t eat any, you starve.
• If you eat just enough to be lean, you’ll keep salivating at the sight of pizzas and ice cream and feel distracted and hungry all the time. Importantly, in this situation, the feeling of hunger does not mean that you should eat more – it’s your brain being overpowered by a superstimulus while being bored.
• And if you eat way too much candy or pizza at once, you’ll be feeling terrible afterwards, however tasty the food was.

Most of us (myself included) sleep 7-9 hours if we don’t have any alarms in the morning and if we get out of bed when we feel like it. Does this mean that 7-9 hours of sleep is the “natural” or the “optimal” amount?

My thesis is: obviously, no. Modern sleep, in its infinite comfort, is an unnatural superstimulus that overwhelms our brains with pleasure and comfort (note: I’m not saying that it’s bad, simply that being in bed today is much more pleasurable than being in “bed” in the past.)

Think about sleep 10,000 years ago. You sleep in a cave, in a hut, or under the sky, with predators and enemy tribes roaming around. You are on a wooden floor, on an animal’s skin, or on the ground. The temperature will probably drop 5-10°C overnight, meaning that if you were comfortable when you were falling asleep, you are going to be freezing when you wake up. Finally, there’s moon shining right at you and all kinds of sounds coming from the forest around you.

In contrast, today: you sleep on your super-comfortable machine-crafted foam of the exact right firmness for you. You are completely safe in your home, protected by thick walls and doors. Your room’s temperature stays roughly constant, ensuring that you stay warm and comfy throughout the night. Finally, you are in a light and sound-insulated environment of your house. And if there’s any kind of disturbance you have eye masks and earplugs.

Does this sound “natural”?

Now, what if the only sleep available to you was modern sleep?

• If you don’t sleep at all, you go crazy, because some amount of sleep is necessary.
• If you sleep just enough to be awake during the day, you’ll be dreaming of getting a nap at the sight of a bed and will be distracted and sleepy all the time. Importantly, I claim, in this situation, the feeling of sleepiness does not mean that you should sleep more – it’s your brain being overpowered by a superstimulus while being bored.
• And if you sleep way too much at once, you’ll be feeling terrible afterwards, however pleasant the sleep was.

Even if I convinced you about the “sleeping too much” part, you are still probably wondering: but what does depression have to do with anything? Isn’t sleeping a lot good for mental health? Well…

Depression <-> oversleeping. Mania <-> acute sleep deprivation

In this section, I argue that depression triggers/amplifies oversleeping while oversleeping triggers/amplifies depression. Similarly, mania triggers/amplifies acute sleep deprivation while acute sleep deprivation triggers/amplifies mania.

One of the most notable facts about sleep is just how interlinked excessive sleep is with depression and how interlinked sleep deprivation is with mania in bipolar people.

Someone in r/BipolarReddit asked: How many hours do you sleep when stable vs (hypo)manic? Depressed?

Here are all 8 answers that compare hours for manic and depressed states, I excluded answers that describe hypomania but do not describe mania or that only describe mania or only describe depression. note the consistency:

• “Manic/hypomanic: 0-6 hours Stable: 7-9 hours Depressed: 10-19 hours”
• “Manic, 2-3, hypo, 5-6, stable 8-9, depressed 10-12. 8 is the number I try to hit.”
• “Severely depressed w/o mixed features - 12 to 15 hours Low to Moderate depressed w/o mixed - 10 hours, if no alarm. With alarm less, but super hangover Stable -Usually 7-9 hours Hypomanic taking sedating evening meds - 5 to 7 hours Hypomanic with no sedating evening meds - 3 to 5 hours Manic out of hand - 0 to 3 hours Manic in hospital put on maximum sedating meds or injections - 4 to 6 hours Mixed episodes = same as hypo(manic)”
• “I try to get at least 8 hours but when I’m depressed I nap a lot. When I’m hypo I sleep pretty much the same but when I’m manic I’m lucky to get 3 hours. Huhs”
• “Just got out of a manic episode. A few all-nighters, a lot of 3 hour nights, and a good night of sleep was 6 hours. Now I’m depressed and I’ve been sleeping from 9pm to noon and staying in bed for much longer after I’m awake.”
• “Manic 2-4, stable 6-7, depressed 10-12”
• “Around 15 hours of sleep per night while depressed, and between 0-4 hours per night while manic.”

Lack of sleep is such a potent trigger for mania that acute sleep deprivation is literally used to treat depression. Aside from ketamine, not sleeping for a night is the only medicine we have to quickly – literally overnight – and reliably (in ~50% of patients) improve mood in depressed patients (until they go to bed, unless you keep advancing their sleep phase Riemann, D., König, A., Hohagen, F., Kiemen, A., Voderholzer, U., Backhaus, J., Bunz, J., Wesiack, B., Hermle, L. and Berger, M., 1999. How to preserve the antidepressive effect of sleep deprivation: A comparison of sleep phase advance and sleep phase delay. European archives of psychiatry and clinical neuroscience, 249(5), pp.231-237. ). NOTE: DO NOT TRY THIS IF YOU ARE BIPOLAR, YOU MIGHT GET A MANIC EPISODE.

Figure 1. Copied from Wehr TA. Improvement of depression and triggering of mania by sleep deprivation. JAMA. 1992 Jan 22;267(4):548-51.

Why does the lack of sleep promote manic states while long sleep promotes depression? I don’t know. But here are a couple of pointers to interesting papers relevant to the question: Can non-REM sleep be depressogenic? Beersma DG, Van den Hoofdakker RH. Can non-REM sleep be depressogenic?. Journal of affective disorders. 1992 Feb 1;24(2):101-8. Brain-derived neurotrophic factor (BDNF) is associated with synapse growth. Sleep deprivation appears to increase BDNF [and therefore neurogenesis?]. Papers that showed up when I googled “sleep deprivation bdnf”: The Brain-Derived Neurotrophic Factor: Missing Link Between Sleep Deprivation, Insomnia, and Depression . Rahmani M, Rahmani F, Rezaei N. The brain-derived neurotrophic factor: missing link between sleep deprivation, insomnia, and depression. Neurochemical research. 2020 Feb;45(2):221-31. The link between sleep, stress and BDNF . Eckert A, Karen S, Beck J, Brand S, Hemmeter U, Hatzinger M, Holsboer-Trachsler E. The link between sleep, stress and BDNF. European Psychiatry. 2017 Apr;41(S1):S282-. BDNF: an indicator of insomnia? . Giese M, Unternährer E, Hüttig H, Beck J, Brand S, Calabrese P, Holsboer-Trachsler E, Eckert A. BDNF: an indicator of insomnia?. Molecular psychiatry. 2014 Feb;19(2):151-2. Recovery Sleep Significantly Decreases BDNF In Major Depression Following Therapeutic Sleep Deprivation . Goldschmied JR, Rao H, Dinges D, Goel N, Detre JA, Basner M, Sheline YI, Thase ME, Gehrman PR. 0886 Recovery Sleep Significantly Decreases BDNF In Major Depression Following Therapeutic Sleep Deprivation. Sleep. 2019 Apr;42(Supplement_1):A356-.

Jeremy Hadfield writes:

My (summarized/simplified) hypothesis based on what I’ve read: depression involves rigid, non-flexible brain states that correspond to rigid depressive world models. Depression also involves a non-updating of models or inability to draw new connections (brain is even literally slightly lighter in depressed patients). Sleep involves revising/simplifying world models based on connections learned during the day, involves pruning unneeded or irrelevant synaptic connections. Thus, excessive sleep + depression = even less world model updating, even more rigid brain, even fewer new connections. Sleep deprivation can resolve this problem at least temporarily by ensuring that you stay awake for longer and keep adding connections, thus compensating for the decreased connection-building caused by depression and “forcing” a brain update (perhaps through neural annealing - see QRI article).

Occasional acute sleep deprivation is good for health and promotes more efficient sleep

One other argument for sleeping the “natural” (7-9) number of hours is that we feel bad on days when we sleep less. In this section, I argue against this line of reasoning by asking: if fasting and exercising are good, shouldn’t acute sleep deprivation also be good? And I conclude that it is probably good.

Let’s continue our analogy of sleep to eating and add exercise to the mix.

It seems to me that most common arguments against acute sleep deprivation equally “demonstrate” that fasting and exercise are bad.

For example, I ran 7 kilometers 2 days ago and my legs still hurt like hell and I can’t run at all. Does this mean that running is “bad”?

Well, consensus seems to be that dizziness, muscle damage (and thus pain) and decreased physical performance after the run, are not just not bad, but are in fact necessary for the organism to train to run faster or to run longer distances by increasing muscle mass, muscle efficiency, and lung capacity.

What about fasting? When I fast, I am more anxious, I think about food a lot, meaning that focus is more difficult, and I feel cold. And if I decided to fast too much, I would pass out and then die. Does this mean that fasting is “bad”? Well, consensus seems to be that occasional fasting actually activates some “good” kind of stress, promotes healthy autophagy, (obviously) helps to lose weight, etc. and is in fact good.

Now, what happens when I sleep for 2 hours instead of 7 one night? I feel somewhat tingly in my hands, my mood is heightened a little bit, and, if I start watching a movie with my wife at 6pm, I’ll fall asleep. Does this mean that sleeping 2 hours one night is bad for my health?

Obviously no. The only thing we observe is that my organism was subjected to acute stress. However, the reaction to acute stress does not tell us anything about the long-term effects of this kind of stress. As we know, both in running and in fasting, short-term acute stress response results in adaptation and in long-term increase in performance and in benefit to the organism.

I combed through a lot of sleep literature and I haven’t seen a single study that made a parallel to either fasting or exercise and I haven’t seen a single pre-registered RCT that tried to see what happens to someone if you subject them to 1-3 nights per week of acute sleep deprivation and allow to recover the rest of the nights. Do they perform better or worse in the long-term on cognitive tests? Do they have more or less inflammation? Do they need less recovery sleep over time?

I think that the answers are:

• Acute sleep deprivation combined with caffeine or some other stimulant that cancels out sleep pressure does not result in decreased cognitive ability at least until 30-40 hours of wakefulness (if this is true, then sleepiness , rather absence of sleep per se is responsible for decreased cognitive performance during acute sleep deprivation).
• Occasional acute sleep deprivation has no impact on long-term cognitive ability or health.
• Sleep does become more efficient over time and, in complete analogy to exercise, you withstand both acute sleep deprivation better and can function at baseline with a lower amount of sleep in the long-term.

(The only parallel to fasting I’m aware of anyone making is by Nassim Taleb… when he was quote-tweeting me.)

Appendix: anecdotes about acute sleep deprivation

Appendix: philipp streicher on homeostasis, its relationship to mania/depression, and on other points i make, our priors about sleep research should be weak.

In this section, I note that most sleep research is extremely unreliable and we shouldn’t conclude much on the basis of it.

Do you believe in power-posing? In ego depletion? In hungry judges and brain training?

If the answer is no, then your priors for our knowledge about sleep should be weak because “sleep science” is mostly just rebranded cognitive psychology, with the vast majority of it being small-n, not pre-registered, p-hacked experiments.

I have been able to find exactly one pre-registered experiment of the impact of prolonged sleep deprivation on cognition. It was published by economists from Harvard and MIT in 2021 and its pre-registered analysis found null or negative effects of sleep on all primary outcomes Bessone P, Rao G, Schilbach F, Schofield H, Toma M. The economic consequences of increasing sleep among the urban poor. The Quarterly Journal of Economics. 2021 Aug;136(3):1887-941. (note that both the abstract and the main body of this paper report results without the multiple-hypothesis correction, in contradiction to the pre-registration plan of the study. The paper does not mention this change anywhere. See comments for the details. ).

So why has sleep research not been facing a severe replication crisis, similar to psychology?

First, compared to psychology, where you just have people fill out questionnaires, sleep research is slow, relatively expensive, and requires specialized equipment (e.g. EEG, actigraphs). So skeptical outsiders go for easier targets (like social psychology) while the insiders keep doing the same shoddy experiments because they need to keep their careers going somehow .

Second, imagine if sleep researchers had conclusively shown that sleep is not important for memory, health, etc. – would they get any funding? No. Their jobs are literally predicated on convincing the NIH and other grantmakers that sleep is important. As Patrick McKenzie notes , “If you want a problem solved make it someone’s project. If you want it managed make it someone’s job.”

Figure 2. Relative risk of showing benefit or harm of treatment by year of publication for large NHLBI trials on pharmaceutical and dietary supplement interventions. Copied from Kaplan RM, Irvin VL. Likelihood of null effects of large NHLBI clinical trials has increased over time. PloS one. 2015 Aug 5;10(8):e0132382.

Figure 3. Eric Turner on Twitter: “Negative depression trials…Now you see ‘em, now you don’t. Published literature vs FDA, from [ Turner EH, Matthews AM, Linardatos E, Tell RA, Rosenthal R. Selective publication of antidepressant trials and its influence on apparent efficacy. New England Journal of Medicine. 2008 Jan 17;358(3):252-60. ]"

Even in medicine, without pre-registered RCTs truth is extremely difficult to come by, with more than one half Kaiser J. More than half of high-impact cancer lab studies could not be replicated in controversial analysis. AAAS Articles DO Group. 2021; of high-impact cancer papers failing to be replicated, and with one half of RCTs without pre-registration of positive outcomes being spun Kaplan RM, Irvin VL. Likelihood of null effects of large NHLBI clinical trials has increased over time. PloS one. 2015 Aug 5;10(8):e0132382. by researchers as providing benefit when there’s none. And this is in medicine, which is infinitely more consequential and rigorous than psychology.

Also see: Appendix: I have no trust in sleep scientists .

Decreasing sleep by 1-2 hours a night in the long-term has no negative health effects

In this section, I outline several lines of evidence that bring me to the conclusion that decreasing sleep by 1-2 hours a night in the long-term has no negative health effects. To summarize:

• A sleep researcher who trains sailors to sleep efficiently in order to maximize their race performance believes that 4.5-5.5 hours of sleep is fine.
• 70% of 84 hunter-gatherers studied in 2013 slept less than 7 hours per day, with 46% sleeping less than 6 hours.
• A single-point mutation can decrease the amount of required sleep by 2 hours, with no negative side-effects.
• A brain surgery can decrease the amount of sleep required by 3 hours, with no negative-side effects.
• Sleep is not required for memory consolidation.
• Claudio Stampi is a Newton, Massachusetts based sleep researcher. But he is not your normal sleep researcher whose career is built on observational studies or p-hacked n=20 experiments that always show “significant” results. He is one of the only sleep researchers with skin in the game: the goal of his research is to maximize performance of sailors by tinkering with their sleep cycles, and he believes that 4.5-5.5 hours of sleep is fine, The article uses the phrase “get by” and does not state that there’s no decrease in performance. However, it does state that the decrease in performance at 3 hours of sleep with lots of naps is 12-25%, so increasing sleep by 50-83% from this, seems unlikely to result in any decrease in performance, compared to 8 hours of sleep (“he had them shift to their three-hour routines. After more than a month, the monophasic group showed a 30 percent loss in cognitive performance. The group that divided its sleep between nighttime and short naps showed a 25 percent drop. But the polyphasic group, which slept exclusively in short naps, showed only a 12 percent drop."). as long as it’s broken down into core sleep and a series of short (usually 20-minute) naps. Here’s Outside :

“Solo sailing is one of the best models of 24/7 activity, and brains and muscles are required,” Stampi said one day at his home, from which he runs the institute. “If you sleep too much, you don’t win. If you don’t sleep enough, you break.” …

“For those sailors who are seriously competing, Stampi is a necessity,” says Brad Van Liew, a 37-year-old Californian who began working with Stampi in 1998 and went on to become America’s most accomplished solo racer and the winner in his class of the 2002-2003 Around Alone, a 28,000-mile global solo race. “You have to sleep efficiently, or it’s like having a bad set of sails or a boat bottom that isn’t prepared properly.” …

both Golding and MacArthur sleep about the same amount while racing, between 4.5 and 5.5 hours on average in every 24—the minimum amount, Stampi believes, on which humans can get by.

In 2013, scientists tracked the sleep of 84 hunter-gatherers from 3 different tribes Yetish G, Kaplan H, Gurven M, Wood B, Pontzer H, Manger PR, Wilson C, McGregor R, Siegel JM. Natural sleep and its seasonal variations in three pre-industrial societies. Current Biology. 2015 Nov 2;25(21):2862-8. (each person’s sleep was measured for about a week but measurements for different groups were taken in different parts of the year). The average amount of sleep among these 84 people was 6.5 hours. Judging by CDC’s “7 hours or more” recommendation , Consensus Conference Panel:, Watson, N.F., Badr, M.S., Belenky, G., Bliwise, D.L., Buxton, O.M., Buysse, D., Dinges, D.F., Gangwisch, J., Grandner, M.A. and Kushida, C., 2015. Joint consensus statement of the American Academy of Sleep Medicine and Sleep Research Society on the recommended amount of sleep for a healthy adult: methodology and discussion. Journal of Clinical Sleep Medicine, 11(8), pp.931-952. 70% out of these 84 undersleep:

• 6 people slept between 4 and 5 hours
• 19 people slept between 5 and 6 hours
• 34 people slept between 6 and 7 hours
• 21 people slept between 7 and 8 hours
• 4 people slept between 8 and 9 hours

One group of hunter-gatherers (10 people from Tsimane tribe studied in November/December of 2013) slept just 5.6 hours on average.

The authors of this study also note that “None of these groups began sleep near sunset, onset occurring, on average, 3.3 hr after sunset” (they are probably getting too much artificial light… or something).

What I’m getting from all of this is: there’s nothing “natural” about sleeping 7-9 hours. If you think that the amount of sleep hunter-gatherers are getting is the amount of sleep humans have evolved to get, then you should not worry at all about getting 4, 5, or 6 hours of sleep a night.

The CDC and the professional sleep researchers pull the numbers out of their asses without any kind of rigorous scientific evidence for their “consensus recommendations”. There’s no causal evidence that sleeping 7-9 hours is healthier than sleeping 6 hours or less. Correlational evidence suggests Shen X, Wu Y, Zhang D. Nighttime sleep duration, 24-hour sleep duration and risk of all-cause mortality among adults: a meta-analysis of prospective cohort studies. Scientific Reports. 2016 Feb 22;6:21480. that people who sleep 4 hours have the same if not lower mortality as those who sleep 8 hours and that people who sleep 6-7 hours have the lowest mortality.

Also see: Appendix: Jerome Siegel and Robert Vertes vs the sleep establishment

It appears that there is a distinct single-point mutation that allows some people to sleep several hours less than typical on average. A Rare Mutation of β1-Adrenergic Receptor Affects Sleep/Wake Behaviors : Shi G, Xing L, Wu D, Bhattacharyya BJ, Jones CR, McMahon T, Chong SC, Chen JA, Coppola G, Geschwind D, Krystal A. A rare mutation of β1-adrenergic receptor affects sleep/wake behaviors. Neuron. 2019 Sep 25;103(6):1044-55.

We have identified a mutation in the β1-adrenergic receptor gene in humans who require fewer hours of sleep than most. In vitro, this mutation leads to decreased protein stability and dampened signaling in response to agonist treatment. In vivo, the mice carrying the same mutation demonstrated short sleep behavior. We found that this receptor is highly expressed in the dorsal pons and that these ADRB1+ neurons are active during rapid eye movement (REM) sleep and wakefulness. Activating these neurons can lead to wakefulness, and the activity of these neurons is affected by the mutation. These results highlight the important role of β1-adrenergic receptors in sleep/wake regulation.

The study compares carriers of the mutation in one family to non-carriers in the same family and finds that carriers sleep about 2 hours per day less. Given the complexity of sleep and the multitude of its functions, it seems extremely implausible that just one mutation in the β1-adrenergic receptor gene was able to increase its efficiency by about 25%. It seems that it just made carriers sleep less (due to more stimulation of a group of neurons in the brain responsible for sleep/wakefulness) without anything else obviously changing when compared to non-carriers.

A similar example of a drop in the amount of sleep required without negative side effects and driven by a single factor was described in Development of a Short Sleeper Phenotype after Third Ventriculostomy in a Patient with Ependymal Cysts . Seystahl K, Könnecke H, Sürücü O, Baumann CR, Poryazova R. Development of a short sleeper phenotype after third ventriculostomy in a patient with ependymal cysts. Journal of Clinical Sleep Medicine. 2014 Feb 15;10(2):211-3. To sum up: a 59-year-old patient had chronic hydrocephalus. An endoscopic third ventriculostomy was performed on him. His sleep dropped from 7-8 hours a night to 4-5 hours a night without him becoming sleepy, he stopped being depressed, and his physical or cognitive performance stayed normal, as measured by the doctors.

Sleep is not required for memory consolidation. Jerome Siegel (the author of the hunter-gatherers study mentioned above) writes in Memory Consolidation Is Similar in Waking and Sleep : Siegel JM. Memory Consolidation Is Similar in Waking and Sleep. Current Sleep Medicine Reports. 2021 Mar;7(1):15-8.

Under interference conditions, such as exist during sleep deprivation, subjects, by staying awake, necessarily interacting with the experimenter keeping them awake and experiencing the laboratory environment, will remember more than just the items that are presented. But they may be less able to recall the particular items the experimenter is measuring. This can lead to the mistaken conclusion that sleep is required for memory consolidation [7].

Recent work has, for the first time, dealt with this issue. It was shown that a quiet waking period or a meditative waking state in which the environment is being ignored, produces a gain in recall similar to that seen in sleep, relative to an active waking state or a sleep-deprived state [8–16]. …

REM sleep has been hypothesized to have a key role in memory consolidation [20]. But it has been reported that near total REM sleep deprivation for a period of 14 to 40 days by administration of the monoamine oxidase inhibitor phenelzine has no apparent effect on cognitive function in humans [21]. A systematic study using serotonin or norepinephrine re-uptake inhibitors to suppress REM sleep in humans had no deleterious effects on a variety of learning tasks [22, 23]. Humans rarely survive the damage to the pontine region which when discretely lesioned in animals greatly reduces or eliminates REM sleep [20, 23–25]. However, one such subject with pontine damage that severely reduced REM sleep has been thoroughly studied. The studies show normal or above normal cognitive performance and no deficit in memory formation or recall [26•]. It has been claimed that learning results in greater total amounts of sleep, or greater amounts of REM sleep [27], or greater amounts of sleep spindles, or slow wave activity. However, a systematic test of this hypothesis in 929 human subjects with night-long EEG recording found no such correlation with retention [28•].

The entire Scientific Consensus™ about sleep being essential for memory consolidation appears to be heavily flawed, driven by people like Matthew Walker, and making me lose the last remnants of trust in sleep science that I had .

Appendix: how I wake up after 6 or less hours of sleep

Appendix: anecdotes about long-term sleep deprivation.

• Appendix: the idea that sleep’s purpose is metabolite clearance, if not total bs, is massively overhyped

Chadwick worked for several nights straight without sleep on the seminal discovery [of the neutron, for which he was awarded the 1935 Nobel in physics]. When he was done he went to a meeting of the Kapitza Club at Cambridge and gave a talk about it, ending with the words, “Now I wish to be chloroformed and put to sleep”.

I’m not what they call a “natural short sleeper”. If I don’t restrict my sleep, I often sleep more than 8 hours and I still struggle with getting out of bed. I used to be really scared of not sleeping enough and almost never set the alarm for less than 7.5 hours after going to bed.

My sleep statistics tells me that I slept an average of 5:25 hours over the last 7 days, 5:49 hours over the last 30 days, and 5:57 over the last 180 days hours, meaning that I’m awake for 18 hours per day instead of 16.5 hours. I usually sleep 5.5-6 hours during the night and take a nap a few times a week when sleepy during the day.

This means that I’m gaining 33 days of life every year. 1 more year of life every 11 years. 5 more years of life every 55 years.

Why are people not all over this? Why is everyone in love with charlatans who say that sleeping 5 hours a night will double your risk of cancer, make you pre-diabetic, and cause Alzheimer’s, despite studies showing that people who sleep 5 hours have the same, if not lower, mortality than those who sleep 8 hours? Convincing a million 20-year-olds to sleep an unnecessary hour a day is equivalent, in terms of their hours of wakefulness, to killing 62,500 of them.

I wrote large chunks of this essay having slept less than 1.5 hours over a period of 38 hours. I came up with and developed the biggest arguments of it when I slept an average of 5 hours 39 minutes per day over the preceding 14 days. At this point, I’m pretty sure that the entire “not sleeping ‘enough’ makes you stupid” is a 100% psyop. It makes you somewhat more sleepy, yes. More stupid, no. I literally did an experiment in which I tried to find changes in my cognitive ability after sleeping 4 hours a day for 12-14 days , I couldn’t find any. My friends who I was talking to a lot during the experiment simply didn’t notice anything.

What do I lose due to sleeping 1.5 hours a day less? I’m somewhat more sleepy every day and staying awake during boring calls is even more difficult now. On the other hand, just a prospect of playing an exciting video game, makes me 100% alert even after sleeping for 2-3 hours. Related: Horne JA, Pettitt AN. High incentive effects on vigilance performance during 72 hours of total sleep deprivation. Acta psychologica. 1985 Feb 1;58(2):123-39. There’s no guarantee that what I’m doing is healthy after all, although, as I explained above, I think that it’s extremely unlikely due to likely adaptation, and likely beneficial effects of sleep deprivation (e.g. increased BDNF, less susceptibility to depression), and since I take a 20-minute nap under my wife’s watch whenever I don’t feel good.

Subscribe to the updates here – I usually send them every 1-2 months (example: last update ):

Acknowledgements

I would like to thank (in reverse alphabetic order): Misha Yagudin , Guy Wilson , Bart Sturm, Ulysse Sabbag , Stephen Malina , Gavin Leech , Anastasia Kuptsova , Jake Koenig , Aleksandr Kotyurgin, Alexander Kim , Basil Halperin , Jeremy Hadfield , Steve Gadd , and Willy Chertman for reading drafts of this essay and for disagreeing with many parts of it vehemently. All errors mine.

Guzey, Alexey. Theses on Sleep. Guzey.com. 2022 February. Available from https://guzey.com/theses-on-sleep/ .

Or download a BibTeX file here .

• One popular sleep tip I’ve come to wholeheartedly believe is the importance of waking up at the same time: from my experience, it does really seem that the organism adjusts the time it is ready to wake up if you keep a consistent schedule.
• observation: I find staying awake during boring lectures impossible and reliably fall asleep during them, regardless of the amount of sleep I’m getting
• observation: I can play video games with little sleep for several days and feel 100% alert (a superstimulus of its own, but still a valuable observation)
• observation: I become sleepy when I’m working on something boring and difficult

Common objections

Objection: “When I’m underslept I notice that I’m less productive.”

Yes, this is expected as per the analogy to exercise I make above . After exercise you are tired but over time you become stronger.

It might be that undersleeping itself causes you to be less productive. However, it might also be the case that there’s an upstream cause that results in both undersleeping and lack of productivity. I think either could be the case depending on the person but understanding what exactly happens is much harder than people typically appreciate when they notice such co-occurrences.

As Nick Wignall notes on Twitter:

People are also not great at distinguishing true sleepiness from tiredness.

Analogy would be: of all the times when you feel hungry, how much of that is true hunger vs a craving?

Also related: when people say that e.g. they have a small child, are doing medical residency, etc. and feel terrible due to undersleep, note that there’s a big difference between being randomly forced to not sleep when you want to sleep and managing one’s sleep consciously. The analogy would be to saying that fasting is bad because if you are forbidden by someone from eating randomly throughout the day.

Objection: “Driving when you are sleepy is dangerous, therefore you are wrong.”

Answer: Yep, I agree that driving while being sleepy is dangerous and I don’t want anyone to drive, to operate heavy machinery, etc. when they are sleepy. This, however, bears no relationship on any of the arguments I make.

Objection: “The graph that shows more sleep being associated with higher doesn’t tell us anything because sick people tend to sleep more.”

Answer: It is true that some diseases lead to prolonged sleep. However, some diseases also lead to shortened sleep. For example, many stroke patients suffer from insomnia Sterr A, Kuhn M, Nissen C, Ettine D, Funk S, Feige B, Umarova R, Urbach H, Weiller C, Riemann D. Post-stroke insomnia in community-dwelling patients with chronic motor stroke: physiological evidence and implications for stroke care. Scientific Reports. 2018 May 30;8(1):8409. and people with fatal familial insomnia struggle with insomnia. Therefore, if you want to make the argument that the association between longer sleep and higher mortality is not indicative of the effect of sleep, you have to accept that the same is true about shorter sleep and higher mortality.

Appendix: I have no trust in sleep scientists

Why do I bother with all of this theorizing? Why do I think I can discover something about sleep that thousands of them couldn’t discover over many decades?

The reason is that I have approximately 0 trust in the integrity of the field of sleep science.

As you might be aware, 2 years ago I wrote a detailed criticism of the book Why We Sleep written by a Professor of Neuroscience at psychology at UC Berkeley, the world’s leading sleep researcher and the most famous expert on sleep, and the founder and director of the Center for Human Sleep Science at UC Berkeley, Matthew Walker.

Here are just a few of biggest issues (there were many more) with the book.

Walker wrote: “Routinely sleeping less than six or seven hours a night demolishes your immune system, more than doubling your risk of cancer”, despite there being no evidence that cancer in general and sleep are related. There are obviously no RCTs on this, and, in fact, there’s not even a correlation between general cancer risk and sleep duration.

Walker falsified a graph from an academic study in the book.

Walker outright fakes data to support his “sleep epidemic” argument. The data on sleep duration Walker presents on the graph below simply does not exist :

Here’s some actual data on sleep duration over time:

By the time my review was published, the book had sold hundreds of thousands if not millions of copies and was praised by the New York Times , The Guardian , and many other highly-respected papers. It was named one of NPR’s favorite books of 2017 while Walker went on a full-blown podcast tour.

Did any sleep scientists voice the concerns they with the book or with Walker? No. They were too busy listening to his keynote at the Cognitive Neuroscience Society 2019 meeting.

Did any sleep scientists voice their concerns after I published my essay detailing its errors and fabrications? No (unless you count people replying to me on Twitter as “voicing a concern”).

Did Walker lose his status in the community, his NIH grants, or any of his appointments? No, no, and no.

I don’t believe that a community of scientists that refuses to police fraud and of which Walker is a foremost representative (recall that he is the director of the Center for Human Sleep Science at UC Berkeley) could be a community of scientists that would produce a trustworthy and dependable body of scientific work.

Appendix: the idea that sleep’s purpose is metabolite clearance, if not total bs, is massively overhyped

Specifically, the original 2013 paper Xie L, Kang H, Xu Q, Chen MJ, Liao Y, Thiyagarajan M, O’Donnell J, Christensen DJ, Nicholson C, Iliff JJ, Takano T. Sleep drives metabolite clearance from the adult brain. science. 2013 Oct 18;342(6156):373-7. accumulated more than 3,000 (!) citations in less than 10 years and is highly misleading.

The paper is called “Sleep Drives Metabolite Clearance from the Adult Brain”. The abstract says:

The conservation of sleep across all animal species suggests that sleep serves a vital function. We here report that sleep has a critical function in ensuring metabolic homeostasis. Using real-time assessments of tetramethylammonium diffusion and two-photon imaging in live mice, we show that natural sleep or anesthesia are associated with a 60% increase in the interstitial space, resulting in a striking increase in convective exchange of cerebrospinal fluid with interstitial fluid. In turn, convective fluxes of interstitial fluid increased the rate of β-amyloid clearance during sleep. Thus, the restorative function of sleep may be a consequence of the enhanced removal of potentially neurotoxic waste products that accumulate in the awake central nervous system.

At the same time, the paper found that anesthesia without sleep results in the same clearance (paper: “Aβ clearance did not differ between sleeping and anesthetized mice”), meaning that clearance is not caused by sleep per se, but instead only co-occurrs with it. Authors did not mention this in the abstract and mistitled the paper, thus misleading the readers. As far as I can tell, literally nobody pointed this out previously.

And on top of all of this “125I-Aβ1-40 was injected intracortically”, meaning that they did not actually find any brain waste products that would be cleared out. This is an exogenous compound that was injected god knows where disrupting god knows what in the brain.

Max Levchin in Founders at Work :

The product wasn’t really finished, and about a week before the beaming at Buck’s I realized that we weren’t going to be able to do it, because the code wasn’t done. Obviously it was really simple to mock it up—to sort of go, “Beep! Money is received.” But I was so disgusted with the idea. We have this security company; how could I possibly use a mock-up for something worth $4.5 million? What if it crashes? What if it shows something? I’ll have to go and commit ritual suicide to avoid any sort of embarrassment. So instead of just getting the mock-up done and getting reasonable rest, my two coders and I coded nonstop for 5 days. I think some people slept; I know I didn’t sleep at all. It was just this insane marathon where we were like, “We have to get this thing working.” It actually wound up working perfectly. The beaming was at 10:00 a.m.; we were done at 9:00 a.m.

/u/CPlusPlusDeveloper on Gwern’s Writing in the Morning :

We know that acute sleep deprivation seems to have a manic and euphoric effect on at least some percent of the population some percent of the time. For example staying up all night is one of the most effective ways to temporarily aleve depression. Of course the problem is that chronic sleep deprivation has the opposite effect, and the temporary mania and euphoria is not sustainable.

My speculative take is that whatever this mechanism, it was the main reason you experienced a productivity boost. By waking up early you intentionally were fighting against your chronobiology, hence adding an element of acute sleep deprivation regardless of how many hours you got the night before. That mania fuels an amphetamine like focus.

The upshot, if my hypothesis is true, is that waking up early would not produce similar gains if you did it everyday. Like the depressive who stays up all night, it may feels like you’ve discovered an intervention that will pay lasting gains. But if you were to actually make it part of your recurring lifestyle, the benefits would stop, and eventually the impact would work in reverse.

Along those lines that’s probably why you naturally tend to stop conforming to that pattern after a few days. As acute sleep deprivation becomes chronic, you’re most likely intuitively recognizing that the pattern has crossed over to the point of being counter-productive.

Lots of writers and software engineers note that their creative juices start flowing by evening extending late into the night - I think this phenomenon is closely related to the one described in the comment above.

Brian Timar :

sleep anecdote- In undergrad I had zero sleep before several major tests; also before quals in grad school. Basically wouldn’t sleep before things I really considered important (this included morning meetings I didn’t want to miss!). On such occasions I would feel:

miserable, then absurd and in a good humor, weirdly elated, then Super PumpedTM, and

really sharp when the test (or whatever) actually started.

Appendix: a well-documented case-study of a person living without sleep for 4 months

Total Wake: Natural, Pathological, and Experimental Limits to Sleep Reduction , Panchin Y, Kovalzon VM. Total Wake: Natural, Pathological, and Experimental Limits to Sleep Reduction. Frontiers in neuroscience. 2021 Apr 7;15:288. quoting Le sommeil, la conscience et l’éveil : Jouvet M. Le sommeil, la conscience et l’éveil. Odile Jacob; 2016 Mar 9.

There is such pathology as Morvan’s disease, in which quasi-wakefulness, which lasted 3,000 h (more precisely, 2,880), or 4 months, was not accompanied by sleep rebound, since the sleep generation system itself was disturbed.” Throughout this period the patient was under continuous polysomnographic control, so his agrypnia was confirmed objectively. Jouvet conclude that “… slow wave (NREM) and paradoxical (REM) sleep are not necessary for life (at least for 4–5 months for the first and about 8 months for the second), and we cannot consider their suppression to be the cause of any serious disorders in the body. A person who had lack of sleep and dreams for 4 months, of which there are only a few minutes of nightly hallucinations, can turn out to read newspapers during the day, make plans, play cards and win, and at the same time lie on the bed in the dark all night without sleep! In conclusion, we admit: this observation makes most theories about the functions of sleep and paradoxical (REM) sleep obsolete at once, but offers nothing else

I once tried to cheat sleep, and for a year I succeeded (strong peak-performance-sailing vibes):

In the summer of 2009, I was finishing the first—and toughest—year of my doctorate. …

To keep up this crazy sleep schedule, I always needed a good reason to wake up the next morning after my 3.5-hour nighttime sleep. So before I went to bed, I reviewed the day gone past and planned what I would do the next day. I’ve carried on with this habit, and it serves me well even today.

But the Everyman schedule was reasonably flexible. Some days when I missed a nap, I simply slept a little more at night. There were also days when I couldn’t manage a single nap, but it didn’t seem to affect me very much the next day.

To the surprise of many, and even myself, I had managed to be on the polyphasic schedule for more than a year. But then came a conference where for a week I could not get a single nap. It was unsettling but I was sure I would be able to get back to sleeping polyphasic without too much trouble.

I was wrong. When I tried to get back into the schedule, I couldn’t find the motivation to do it; I didn’t have the same urgent goals that I had had a year ago. So I returned to sleeping like an average human.

James Gleck in Chaos on Mitch Feigenbaum:

In the spring of 1976 he entered a mode of existence more intense than any he had lived through. He would concentrate as if in a trance, programming furiously, scribbling with his pencil, programming again. He could not call C division for help, because that would mean signing off the computer to use the telephone, and reconnection was chancy. He could not stop for more than five minutes’ thought, because the computer would automatically disconnect his line. Every so often the computer would go down anyway, leaving him shaking with adrenaline. He worked for two months without pause. His functional day was twenty-two hours. He would try to go to sleep in a kind of buzz, and awaken two hours later with his thoughts exactly where he had left them. His diet was strictly coffee. (Even when healthy and at peace, Feigenbaum subsisted exclusively on the reddest possible meat, coffee, and red wine. His friends speculated that he must be getting his vitamins from cigarettes.)

In the end, a doctor called it off. He prescribed a modest regimen of Valium and an enforced vacation. But by then Feigenbaum had created a universal theory.

Ryan Kulp’s experience with decreasing the amount of sleep by several hours :

i began learning to code in 2015. since i was working full-time i needed to maximize after-hours to learn quickly. i experimented for 10 days straight… go to sleep at 4am, wake up at 8am for work. felt fine.

actually, the first 5-10 minutes of “getting up” after 3-4 hours of sleep sucks more than if i sleep ~8 hours. but after 15 mins of moving around, a shower, etc, i feel as if i slept 8 hours.

since then i’ve routinely slept 4-6 hours /day and definitely been more productive. i think if more people experimented for themselves and had the same “aha” moment i did (that you feel fine after the initial gut-wrenching “i slept too little” reaction), they’d get more done too.

This is a very good point that shows that: there’s (1) how sleepy we feel when waking up and (2) how sleepy we feel during the day. (2) is probably more important but most people are focused on (1) and the implicit assumption is that poor (1) leads to (2) – which is unwarranted.

Also: https://twitter.com/BroodVx/status/1492227577896787969,

Nabeel Qureshi writes:

you’re combining two things here: (1) your brain is overpowered by the comfy soft temp-controlled bed (2) you’re bored. they might both be right but i think you conflate them, and they’re separate arguments. this is important bc i think the strongest counterargument to what you’re saying is the classic experience of: you force yourself to wake up early (say 6), you have a project you’re genuinely excited about (hence #2 is false), but when you sit down to work, you’re tired and can’t quite focus. in this scenario, i think your theory would say that i’m not really that excited about what i’m doing, because if i were (see video game argument) then i’d be awake. i’d disagree and say that the researcher should just go take a nap, and they’ll probably be able to make more progress per hour than the extra hours they gain… trying to force yourself to do something while underslept, subjectively, feels hellish. i’m sure you’ve had this experience - did you figure out a workaround?

It is completely true that if you are excited by a project but it’s not super stimulating, it’s still very easy to wake up after less than usual number of hours of sleep and feel sleepy and terrible. This is true for me as well. I found a solution to this: instead of heading straight to the computer, I first unload the clean plates from the dishwasher and load it with dirty plates. This activity is quite special in that it is:

• Why this matters: moving around wakes up the body much better than just sitting.
• Why this matters: moving around in automatic pre-defined movements eventually results in the brain just performing these movements on autopilot without waking up.
• Why this matters: I and people I know tend to find intense physical activities right after waking up really unpleasant and somewhat nauseating.

In about 90% of the cases, 10 minutes later when I’m done with the dishwasher, I find that I’m fully awake and don’t actually want to sleep anymore. In the remaining 10% of the cases, I stay awake and work until my wife wakes up and then go take a 20-minute nap under her watch (and take as many 20-minute naps as I need during the day, although I only end up taking a few naps a week and rarely more than one per day, unless I’m sick).

Appendix: Elon Musk on working 120 hours a week and sleep

On Tesla’s first-quarter earnings conference call in May, Musk referred to inquiries from Wall Street analysts as “boring, bonehead questions” and as “so dry. They’re killing me.” On the next earnings conference call in August, Musk said he was sorry for “being impolite” on the previous call.

“Obviously I think there’s really no excuse for bad manners and I was violating my own rule in that regard. There are reasons for it, I got no sleep, 120 hour weeks, but nonetheless, there is still no excuse, so my apologies for not being polite on the prior call,” Musk said.

Later in August, in conversation with the New York Times, Musk reported using prescription sleep medication Ambien to sleep.

“Yeah. It’s not like for fun or something,” Musk told Swisher Wednesday. “If you’re super stressed, you can’t go to sleep. You either have a choice of, like, okay, I’ll have zero sleep and then my brain won’t work tomorrow, or you’re gonna take some kind of sleep medication to fall asleep.”

Musk said he was working such insane hours to get Tesla through the ramp up in production for its Model 3 vehicle. ”[A]s a startup, a car company, it is far more difficult to be successful than if you’re an established, entrenched brand. It is absurd that Tesla is alive. Absurd! Absurd.”

Philipp ( @Cautes ):

First, I wanted to share a way of thinking about some of your findings that builds on the idea of a homeostatic control system (brought to you from engineering via cybernetics). The classic example is a thermostat, which keeps temperature of a room close to a set point. Biology is quite a bit more messy than this, of course, but the body makes use of a plenty of feedback mechanisms to stay close to set points as well. You’re right in pointing out that these set points don’t need to be healthy though. For example, measured via EEG, PTSD patients have alpha power (which primarily modulates neural inhibition in frontal, parietal and occipital areas of the brain) set points far below that of healthy control groups. One way to deal with these suboptimal set points is to simply disrupt the system. Here’s a model that makes this point nicely: imagine all possible brain state dynamics as a two-dimensional plane and place a ball on it which represents the current brain state space. As the ball moves, the brain dynamics change as well (in frequency, phase, amplitude - you name it). On the plane, you have basins that give stability to the brain state, and repellers in the form of hills, as well as random noise and outside interference which drives the ball into various directions. Sometimes the ball will get stuck in basins which are highly suboptimal, but they are deep enough that exploration of other set points is not possible. If the system is disrupted, the ball might get jolted out of its basin though, and be again able to fall into a more optimal position.

With that said, there’s plenty of evidence that stability in itself (even within better basins) is suboptimal for perfect health, because contexts change. For example, people who are very physically healthy (athletes, for example), tend to have far greater variance in the time interval between individual heart beats (heart rate variability) than even the average person, and as the average person gets healthier, their heart rate variability increases as well. Basically, the body becomes more resilient by introducing a noise signal that produces chaotic fluctuations to homeostatic control mechanisms (controlled allostasis) and there are good reasons to think that this is true of psychological health as well.

Because of this, I think that you’re right in suggesting that varying the amount of time you sleep is a good thing - especially if you’re currently struggling with depression or mania. Not even necessarily because sleep per se is the culprit, but because it might dislodge a ball stuck in a suboptimal basin, so to speak. Depressed people tend to oversleep, people with mania tend to sleep too little, so steering in the opposite direction is only logical. For perfectly healthy people, sleep cycling is probably the best way to go - kind of a mirroring the logic of heart rate variability: introduce some noise to keep your body on your toes. It’s just like fasting, working out, cold exposure, saunas, etc. - it’s al about producing stressors on the body which stir up repair processes which keep you healthy (and biologically younger). I have done plenty of self-experiments with polyphasic 5-6 hour sleeping (similar to the the approach studied by Stampi, who you mentioned), with no negative consequences. The main thing that makes it impractical is that intermittent napping is sometimes hard to combine with professional responsibilities and a social life.

As a side note, because you ask the question about why depressed people sleep longer, and people with mania sleep less, the answer to this is very likely highly multi-causal. With that said, I wanted to point out that depressed people generally exhibit excessive alpha activity in eyes-open waking states, which normally becomes more pronounced in people as they drift off to sleep (because of the neural inhibition function). We also have reason to believe that it mediates between BDNF and subclinical depressed mood, so that’s a link to something else you talk about in your article. As for mania, I haven’t looked at this myself, but I remember hearing that it’s almost a mirror image, with generally decreased synchronisation of slower oscillations and heightened faster rhythms, generally associated with greater arousal and wakefulness.

One last thing: as you point out, sleep is likely not required for memory retention. Any claim that sleep is about any specific cognitive function should be suspect on the principle that the phenomenon of sleep predates the development of organisms with brains - it can’t have evolved specifically for something as high-level as memory retention. It’s more likely about something more basic like general metabolic health.

Appendix: Jerome Siegel and Robert Vertes vs the sleep establishment

Time for the Sleep Community to Take a Critical Look at the Purported Role of Sleep in Memory Processing Vertes RP, Siegel JM. Time for the sleep community to take a critical look at the purported role of sleep in memory processing. Sleep. 2005 Oct 1;28(10):1228-9. by Robert Vertes and Jerome Siegel (a reply to Walker claiming that the debate on memory processing in sleep is essentially settled):

The present ‘debate’ was sparked by an editorial by Robert Stickgold in SLEEP on an article in that issue by Schabus et a on paired associate learning and sleep spindles in humans

Regarding Stickgold’s editorial, I was particularly troubled by his opening statement, as follows: “The study of sleep-dependent memory consolidation has moved beyond the question of whether it exists to questions of its extent and of the mechanisms supporting it”. He then proceeded to cite evidence justifying this statement. Surprisingly, there was no mention of opposing views or a discussion of data inconsistent with the sleep-memory consolidation (S-MC) hypothesis. It seemed that the controversial nature of this issue should have at least been acknowledged, but apparently to do so would have undermined Stickgold’s position that the door is closed on this debate and only the fine points need be resolved. …

By all accounts, sleep does not serve a role in declarative memory. As reviewed by Smith, with few exceptions, reports have shown that depriving subjects of REM sleep does not disrupt learning/memory, or exposure to intense learning situations does not produce subsequent increases in REM sleep. Smith concluded: “REM sleep is not involved with consolidation of declarative material.” The study by Schabus et al (see above) is another example that the learning of declarative material is unaffected by sleep. They reported that subjects showed no significant difference in the percentage of word-pairs correctly recalled before and after 8 hours of sleep. Or as Stickgold stated in his editorial [the editorial Vertes and Siegel are replying to], “Performance in the morning was essentially unchanged from the night before”. It would seem important for Stickgold/Walker to acknowledge that the debate on sleep and memory has been reduced to a consideration of procedural memory – to the exclusion of declarative memory. If there are exceptions, they should note. Several lines of evidence indicate that REM sleep is not involved in memory processing/consolidation – or at least not in humans. Perhaps the strongest argument for this is the demonstration that the marked suppression or elimination of REM sleep in individuals with brainstem lesions or on antidepressant drugs has no detrimental effect on cognition. A classic case is that of an Israeli man who at the age of 19 suffered damage to the brainstem from shrapnel from a gunshot wound, and when examined at the age of 33 he showed no REM sleep. The man, now 55, is a lawyer, a painter and interestingly the editor of a puzzle column for an Israeli magazine. Recently commenting on his ‘famous’ patient, Peretz Lavie stated that “he is probably the most normal person I know and one of the most successful ones”. There are several other well documented cases of individuals with greatly reduced or absent REM sleep that exhibit no apparent cognitive deficits. It would seem that these individuals would be a valuable resource for examining the role of sleep in memory. …

In Memory Consolidation Is Similar in Waking and Sleep cited above, Siegel notes: Siegel JM. Memory Consolidation Is Similar in Waking and Sleep. Current Sleep Medicine Reports. 2021 Mar;7(1):15-8.

To critically evaluate this hypothesis [that sleep has a critical role in memory consolidation], we must take “interference” effects into account. If you learn something before or after the experimenter induced learning that is being measured in the typical sleep-memory study, it degrades recall of the tested information. For example if you tell a subject that the capital of Australia is Canberra and then allow the subject to have a normal night’s sleep, there is a high probability that the subject will remember this upon awakening. If on the other hand you tell the subject that the capital of Australia is Canberra, the capital of Brazil is Brasilia, the capital of Canada is Ottawa, the capital of Iceland is Reykjavik, the capital of Libya is Tripoli, the capital of Pakistan is Islamabad, etc., it is much less likely the subject will remember the capital of Australia. The effect of proactive and retroactive interference is dependent on the temporal juxtaposition, complexity, and similarity of the encountered material to the associations being tested. Interference is a well-established concept in the learning literature [1–6]. Under interference conditions, such as exist during sleep deprivation, subjects, by staying awake, necessarily interacting with the experimenter keeping them awake and experiencing the laboratory environment, will remember more than just the items that are presented. But they may be less able to recall the particular items the experimenter is measuring. This can lead to the mistaken conclusion that sleep is required for memory consolidation [7].

Fur Seals Suppress REM Sleep for Very Long Periods without Subsequent Rebound : Lyamin OI, Kosenko PO, Korneva SM, Vyssotski AL, Mukhametov LM, Siegel JM. Fur seals suppress REM sleep for very long periods without subsequent rebound. Current Biology. 2018 Jun 18;28(12):2000-5.

Virtually all land mammals and birds have two sleep states: slow-wave sleep (SWS) and rapid eye movement (REM) sleep [1, 2]. After deprivation of REM sleep by repeated awakenings, mammals increase REM sleep time [3], supporting the idea that REM sleep is homeostatically regulated. * Some evidence suggests that periods of REM sleep deprivation for a week or more cause physiological dysfunction and eventual death [4, 5]. However, separating the effects of REM sleep loss from the stress of repeated awakening is difficult [2, 6]. The northern fur seal (Callorhinus ursinus) is a semiaquatic mammal [7]. It can sleep on land and in seawater. The fur seal is unique in showing both the bilateral SWS seen in most mammals and the asymmetric sleep previously reported in cetaceans [8]. Here we show that when the fur seal stays in seawater, where it spends most of its life [7], it goes without or greatly reduces REM sleep for days or weeks. After this nearly complete elimination of REM, it displays minimal or no REM rebound upon returning to baseline conditions. Our data are consistent with the hypothesis that REM sleep may serve to reverse the reduced brain temperature and metabolism effects of bilateral nonREM sleep, a state that is greatly reduced when the fur seal is in the seawater, rather than REM sleep being directly homeostatically regulated. This can explain the absence of REM sleep in the dolphin and other cetaceans and its increasing proportion as the end of the sleep period approaches in humans and other mammals.

Appendix: more papers I found interesting

The end of sleep: ‘Sleep debt’ versus biological adaptation of human sleep to waking needs : Horne J. The end of sleep:‘sleep debt’versus biological adaptation of human sleep to waking needs. Biological psychology. 2011 Apr 1;87(1):1-4.

It is argued that the latter part of usual human sleep is phenotypically adaptable (without ‘sleep debt’) to habitual shortening or lengthening, according to environmental influences of light, safety, food availability and socio-economic factors, but without increasing daytime sleepiness. Pluripotent brain mechanisms linking sleep, hunger, foraging, locomotion and alertness, facilitate this time management, with REM acting as a ‘buffer’ between wakefulness and nonREM (‘true’) sleep. The adaptive sleep range is approximately 6–9 h, although, a timely short (<20 min) nap can equate to 1 h ‘extra’ nighttime sleep. Appraisal of recent epidemiological findings linking habitual sleep duration to mortality and morbidity points to nominal causal effects of sleep within this range. Statistical significance, here, may not equate to real clinical significance. Sleep durations outside 6–9 h are usually surrogates of common underlying causes, with sleep associations taking years to develop. Manipulation of sleep, alone, is unlikely to overcome these health effects, and there are effective, rapid, non-sleep, behavioural countermeasures. Sleep can be taken for pleasure, with minimal sleepiness; such ‘sleepability’ is ‘unmasked’ by sleep-conducive situations. Sleep is not the only anodyne to sleepiness, but so is wakefulness, inasmuch that some sleepiness disappears when wakefulness becomes more challenging and eventful. A more ecological approach to sleep and sleepiness is advocated.

Long-term moderate elevation of corticosterone facilitates avian food-caching behaviour and enhances spatial memory Pravosudov VV. Long-term moderate elevation of corticosterone facilitates avian food-caching behaviour and enhances spatial memory. Proceedings of the Royal Society of London. Series B: Biological Sciences. 2003 Dec 22;270(1533):2599-604.

It is widely assumed that chronic stress and corresponding chronic elevations of glucocorticoid levels have deleterious effects on animals' brain functions such as learning and memory. Some animals, however, appear to maintain moderately elevated levels of glucocorticoids over long periods of time under natural energetically demanding conditions, and it is not clear whether such chronic but moderate elevations may be adaptive. I implanted wild–caught food–caching mountain chickadees (Poecile gambeli), which rely at least in part on spatial memory to find their caches, with 90–day continuous time–release corticosterone pellets designed to approximately double the baseline corticosterone levels. Corticosterone–implanted birds cached and consumed significantly more food and showed more efficient cache recovery and superior spatial memory performance compared with placebo–implanted birds. Thus, contrary to prevailing assumptions, long–term moderate elevations of corticosterone appear to enhance spatial memory in food–caching mountain chickadees. These results suggest that moderate chronic elevation of corticosterone may serve as an adaptation to unpredictable environments by facilitating feeding and food–caching behaviour and by improving cache–retrieval efficiency in food–caching birds.

Racemic Ketamine as an Alternative to Electroconvulsive Therapy for Unipolar Depression: A Randomized, Open-Label, Non-Inferiority Trial (KetECT) (via Tomas Roos ): Ekstrand J, Fattah C, Persson M, Cheng T, Nordanskog P, Åkeson J, Tingström A, Lindström M, Nordenskjöld A, Movahed RP. Racemic Ketamine as an Alternative to Electroconvulsive Therapy for Unipolar Depression:: A Randomized, Open-Label, Non-Inferiority Trial (KetECT). International Journal of Neuropsychopharmacology. 2021.

Background Ketamine has emerged as a fast-acting and powerful antidepressant, but no head to head trial has been performed, Here, ketamine is compared with electroconvulsive therapy (ECT), the most effective therapy for depression.

Methods Hospitalized patients with unipolar depression were randomized (1:1) to thrice-weekly racemic ketamine (0.5 mg/kg) infusions or ECT in a parallel, open-label, non-inferiority study. The primary outcome was remission (Montgomery Åsberg Depression Rating Scale score ≤10). Secondary outcomes included adverse events (AEs), time to remission, and relapse. Treatment sessions (maximum of 12) were administered until remission or maximal effect was achieved. Remitters were followed for 12 months after the final treatment session.

Results In total 186 inpatients were included and received treatment. Among patients receiving ECT, 63% remitted compared with 46% receiving ketamine infusions (P = .026; difference 95% CI 2%, 30%). Both ketamine and ECT required a median of 6 treatment sessions to induce remission. Distinct AEs were associated with each treatment. Serious and long-lasting AEs, including cases of persisting amnesia, were more common with ECT, while treatment-emergent AEs led to more dropouts in the ketamine group. Among remitters, 70% and 63%, with 57 and 61 median days in remission, relapsed within 12 months in the ketamine and ECT groups, respectively (P = .52).

Conclusion Remission and cumulative symptom reduction following multiple racemic ketamine infusions in severely ill patients (age 18–85 years) in an authentic clinical setting suggest that ketamine, despite being inferior to ECT, can be a safe and valuable tool in treating unipolar depression.

Beersma DG, Van den Hoofdakker RH. Can non-REM sleep be depressogenic?. Journal of affective disorders. 1992 Feb 1;24(2):101-8.

Bessone P, Rao G, Schilbach F, Schofield H, Toma M. The economic consequences of increasing sleep among the urban poor. The Quarterly Journal of Economics. 2021 Aug;136(3):1887-941.

Consensus Conference Panel:, Watson, N.F., Badr, M.S., Belenky, G., Bliwise, D.L., Buxton, O.M., Buysse, D., Dinges, D.F., Gangwisch, J., Grandner, M.A. and Kushida, C., 2015. Joint consensus statement of the American Academy of Sleep Medicine and Sleep Research Society on the recommended amount of sleep for a healthy adult: methodology and discussion. Journal of Clinical Sleep Medicine, 11(8), pp.931-952.

Eckert A, Karen S, Beck J, Brand S, Hemmeter U, Hatzinger M, Holsboer-Trachsler E. The link between sleep, stress and BDNF. European Psychiatry. 2017 Apr;41(S1):S282-.

Ekstrand J, Fattah C, Persson M, Cheng T, Nordanskog P, Åkeson J, Tingström A, Lindström M, Nordenskjöld A, Movahed RP. Racemic Ketamine as an Alternative to Electroconvulsive Therapy for Unipolar Depression:: A Randomized, Open-Label, Non-Inferiority Trial (KetECT). International Journal of Neuropsychopharmacology. 2021.

Giese M, Unternährer E, Hüttig H, Beck J, Brand S, Calabrese P, Holsboer-Trachsler E, Eckert A. BDNF: an indicator of insomnia?. Molecular psychiatry. 2014 Feb;19(2):151-2.

Goldschmied JR, Rao H, Dinges D, Goel N, Detre JA, Basner M, Sheline YI, Thase ME, Gehrman PR. 0886 Recovery Sleep Significantly Decreases BDNF In Major Depression Following Therapeutic Sleep Deprivation. Sleep. 2019 Apr;42(Supplement_1):A356-.

Horne J. The end of sleep:‘sleep debt’versus biological adaptation of human sleep to waking needs. Biological psychology. 2011 Apr 1;87(1):1-4.

Horne JA, Pettitt AN. High incentive effects on vigilance performance during 72 hours of total sleep deprivation. Acta psychologica. 1985 Feb 1;58(2):123-39.

Kaiser J. More than half of high-impact cancer lab studies could not be replicated in controversial analysis. AAAS Articles DO Group. 2021;

Kaplan RM, Irvin VL. Likelihood of null effects of large NHLBI clinical trials has increased over time. PloS one. 2015 Aug 5;10(8):e0132382.

Lyamin OI, Kosenko PO, Korneva SM, Vyssotski AL, Mukhametov LM, Siegel JM. Fur seals suppress REM sleep for very long periods without subsequent rebound. Current Biology. 2018 Jun 18;28(12):2000-5.

Pravosudov VV. Long-term moderate elevation of corticosterone facilitates avian food-caching behaviour and enhances spatial memory. Proceedings of the Royal Society of London. Series B: Biological Sciences. 2003 Dec 22;270(1533):2599-604.

Turner EH, Matthews AM, Linardatos E, Tell RA, Rosenthal R. Selective publication of antidepressant trials and its influence on apparent efficacy. New England Journal of Medicine. 2008 Jan 17;358(3):252-60.

Rahmani M, Rahmani F, Rezaei N. The brain-derived neurotrophic factor: missing link between sleep deprivation, insomnia, and depression. Neurochemical research. 2020 Feb;45(2):221-31.

Riemann, D., König, A., Hohagen, F., Kiemen, A., Voderholzer, U., Backhaus, J., Bunz, J., Wesiack, B., Hermle, L. and Berger, M., 1999. How to preserve the antidepressive effect of sleep deprivation: A comparison of sleep phase advance and sleep phase delay. European archives of psychiatry and clinical neuroscience, 249(5), pp.231-237.

Seystahl K, Könnecke H, Sürücü O, Baumann CR, Poryazova R. Development of a short sleeper phenotype after third ventriculostomy in a patient with ependymal cysts. Journal of Clinical Sleep Medicine. 2014 Feb 15;10(2):211-3.

Shen X, Wu Y, Zhang D. Nighttime sleep duration, 24-hour sleep duration and risk of all-cause mortality among adults: a meta-analysis of prospective cohort studies. Scientific Reports. 2016 Feb 22;6:21480.

Shi G, Xing L, Wu D, Bhattacharyya BJ, Jones CR, McMahon T, Chong SC, Chen JA, Coppola G, Geschwind D, Krystal A. A rare mutation of β1-adrenergic receptor affects sleep/wake behaviors. Neuron. 2019 Sep 25;103(6):1044-55.

Siegel JM. Memory Consolidation Is Similar in Waking and Sleep. Current Sleep Medicine Reports. 2021 Mar;7(1):15-8.

Sterr A, Kuhn M, Nissen C, Ettine D, Funk S, Feige B, Umarova R, Urbach H, Weiller C, Riemann D. Post-stroke insomnia in community-dwelling patients with chronic motor stroke: physiological evidence and implications for stroke care. Scientific Reports. 2018 May 30;8(1):8409.

Vertes RP, Siegel JM. Time for the sleep community to take a critical look at the purported role of sleep in memory processing. Sleep. 2005 Oct 1;28(10):1228-9.

Xie L, Kang H, Xu Q, Chen MJ, Liao Y, Thiyagarajan M, O’Donnell J, Christensen DJ, Nicholson C, Iliff JJ, Takano T. Sleep drives metabolite clearance from the adult brain. science. 2013 Oct 18;342(6156):373-7.

Yetish G, Kaplan H, Gurven M, Wood B, Pontzer H, Manger PR, Wilson C, McGregor R, Siegel JM. Natural sleep and its seasonal variations in three pre-industrial societies. Current Biology. 2015 Nov 2;25(21):2862-8.

Youngstedt SD, Goff EE, Reynolds AM, Kripke DF, Irwin MR, Bootzin RR, Khan N, Jean-Louis G. Has adult sleep duration declined over the last 50+ years?. Sleep medicine reviews. 2016 Aug 1;28:69-85.

Subscribe to receive updates ( archive ):

• Research & Discovery

Getting Sleepy? Check Your Heart Health

Share this:.

Virend Somers, M.D., Ph.D. , thinks you should probably be sleeping in later.

“Using an alarm clock, by definition, means that you haven’t had enough sleep,” says Dr. Somers, Alice Sheets Marriott Professor at Mayo Clinic. “When you wake up artificially, your body has not yet decided to wake up. The best way to sleep is to be able to wake up in the morning refreshed, without an alarm clock.”

While that may be aspirational, it does speak to the cardiologist and sleep expert’s conviction regarding the benefits of sleep.

Sleep and Heart Health

At Mayo Clinic, Dr. Somers leads a team studying the relationship between sleep disorders and cardiovascular disease, including the impacts of conditions such as sleep apnea and excessive daytime sleepiness (EDS). Thanks to support from Sleep Number , his research has uncovered a strong relationship between how sleepy someone is during the daytime and their risk of heart problems.

In a study published in 2021, Dr. Somers and his team found that nearly 1 in 5 people out of 10,000 participants reported experiencing EDS. In addition, people who said they felt “overly sleepy” often or always during the daytime were at 2 ½ times greater risk of dying due to heart issues when compared to those who did not feel so sleepy. This was completely independent of any other sleep issues or disorders.

“We have only recently begun to really understand how important daytime sleepiness is,” Dr. Somers says. “Usually the focus is on problems that affect nighttime sleep, but EDS is its own issue with its own implications.”

Uncovering the Link

Dr. Somers has been in the sleep game for long enough to see how far the research has come. “I became interested in sleep because of some interesting nighttime blood pressure findings during my Ph.D. studies. At that time, there was very little being done in this area,” he says. “Sleep occupies a third of our lives, but the research was limited to just a few centers and was focused on neurology and pulmonology. I wanted to understand how sleep might be affecting heart health, and that was the road less traveled.”

A year after his initial study, Dr. Somers examined the relationship between nervous system activity in people with obstructive sleep apnea, excessive daytime sleepiness, and heart health, finding that patients with sleep apnea who had clinically observed EDS had higher diastolic blood pressure and increased sympathetic nervous system activity compared to those who did not have EDS, which may be linked with greater cardiovascular morbidity.

“Our research is finding this risk is independent of whether someone is experiencing other sleep problems,” says Dr. Somers. “How sleepy someone feels during times when they are supposed to be awake seems to be associated with significant health risks.”

His research continues to dissect the relationship between sleep and cardiovascular disease, seeking to better understand who is most at risk. In a 2023 study, his team examined a cohort of nearly 15,000 patients with obstructive sleep apnea and found that women who had the condition and experienced excessive daytime sleepiness were at higher risk of dying prematurely compared to others. In men, EDS did not increase their mortality risk, though both men and women with sleep apnea and EDS were at higher risk of developing diabetes.  

“This means that when dealing with sleep disorders, sleep apnea or even just heart disease, it’s important for clinicians to ask their patients — especially their female patients — not only about their sleep habits, but also about how sleepy they feel during the day,” says Dr. Somers.

How sleepy someone feels during times when they are supposed to be awake seems to be associated with significant health risks. — Virend Somers, M.D., Ph.D.

Seeking Clarity for Future Treatments

Even as he assesses his patients for their sleepiness and heart health risk, Dr. Somers says there are still many unanswered questions about this relationship: Do daytime sleepiness and heart disease develop in parallel? Does one cause the other? Are the mechanisms of sleepiness causing damage to our blood vessels, resulting in cardiovascular disease?  

Going forward, his team plans to dig into the physiological and biochemical underpinnings of this relationship in the hope of better understanding what factors are at play in excessive sleepiness and heart disease. Understanding these interactions will be the key to addressing heart health risk for these patients and ultimately identifying treatment targets.  

“This is the beauty of mechanistic research,” he says. “We’re focused not just on the phenomenon, but also understanding the underlying mechanism, because once we know the mechanism, we’ll have some ideas on how we might intervene to treat it.”

This research has been conducted in collaboration with Sleep Number . Through a corporate partnership, Sleep Number and Mayo Clinic are working together to deepen knowledge on the relationship between sleep, sleep disorders and cardiovascular health. Sleep Number also supports Mayo Clinic research in other areas of sleep research, including studies on the prevalence of disordered sleep among Somali patients and the relationship between disrupted sleep and markers of aging.

Related Content

CAR-T cell therapy has transformed cancer treatment options — giving more patients hope.

Mayo Clinic researchers have identified a neural circuit in the mouse brain that influences compulsive drug and alcohol use.

Robotic compounding ensures safer, more accurate medications.

• ErasmusJobs
• Green Erasmus

The Importance of Sleep

Constantly tired, grey faces with red, puffy eyes, hands holding cups loaded with caffeine… Lack of sleep seems to be a plague among the modern youth. We live in a constant rush, our schedules are overflowing with various tasks and responsibilities, and rest usually ends up as the lowest priority on our lists. People tend to underestimate the importance of good-quality sleep, without realising the consequences. Moreover, many of us don’t know what “quality sleep” even means – how long we should sleep, how to make sure we actually get enough rest and how to take care of appropriate sleep hygiene. This article will be your first step to finally getting a good night’s sleep.

First things first – do you know why sleep is so important? We all know that sleep is the time when our body and brain regenerate. Let's get down to a bit of science: it is the time when your heart and blood vessels heal and repair, protecting you from heart and kidney diseases, strokes and low blood pressure. Sleep is also an important factor for lowering the risk of diabetes, as it affects how your body reacts to insulin (the hormone that controls your blood sugar level).

If you still don’t feel convinced, good sleep can help you maintain appropriate body weight! Have you noticed that when you are sleepy, you are also more prone to reaching for comfort foods instead of healthy, nutritious meals?  Night time is when your body produces hormones, including ghrelin and leptin – hormones responsible for feeling hungry and full. What this actually means is that sleep deprivation lowers your metabolism, making you more likely to gain weight.

Good sleep is important for your mind as well. Obviously, feeling well-rested affects your mood, response time, and efficiency at work. Studies show that sleep has a crucial impact on activity in some parts of the brain. If you're tired, you may have trouble making decisions, solving problems, controlling your emotions and behaviour, and coping with change.

Now that you know why you should always get enough sleep, it’s time to find out how. Have you ever wondered how much sleep is “enough”? Or if there is such a thing as too much sleep? For an adult, the appropriate amount is between 7 and 9 hours. This means that sleeping over 9 hours per day can actually be bad for you. Oversleeping has similar effects to sleep deprivation: over time it can also lead to diabetes, obesity, and heart disease. More common effects of sleeping too much are headaches, lack of energy or depression. Sounds familiar? Remember that anything in excess is bad.

It’s not only how much sleep you get that’s important – if the quality of sleep is not right, you will not get its full benefits. There are a few tricks that can help you get as much rest as possible. You need to take care of a proper sleep hygiene. Firstly, remember that your bed should be reserved for sleep only – if you have a habit of working or eating in bed you should try to move it to somewhere else. Studies prove that separating workspace and sleeping space can help you fall asleep faster and sleep better throughout the night. And there’s bad news for those addicted to phones – the blue light from the screen disrupts natural sleep patterns by affecting melatonin (sleep hormone) levels. Does avoiding touching your phone and laptop for two hours before sleep sound impossible? At least switch all of your devices to night shift mode – it gives a yellow tint to your display, minimising the negative effect on your hormones. If your device doesn’t have a built-in night mode, you can try Twiligh t (for Android) or f.lux (for Windows).

If you have trouble falling asleep, you should try going to bed and waking up around the same time each day. It might be challenging, especially during weekends, but once you establish a routine, waking up early during the week becomes much easier.  Humans are creatures of habit, so having a nice bedtime routine – a time for you to unwind, relax, and get ready for bed - is the first step to good quality sleep. You can pick out an outfit and pack your bag for the following day, have a nice, warm bath, listen to some music, set time to read a book… try out what works best for you and stick to it!

Maybe it sounds like a lot of restrictions, hard to keep up with when you have a fully packed schedule and tight deadlines –  but still, sleep should be a priority. You’ll be much more efficient finishing everything in your crowded schedule with a rested brain, good energy, and positive attitude – not to mention that after a full night of sleep, those busy days will also feel better. Don’t you think it is worth sacrificing one thing in order to get proper rest? In the long run, it will bring you much more benefit and help you manage your time and tasks better. Good luck – and sleep well!

P.S. You can read up more about the science of sleep here .

Related articles

Reality check time: Erasmus is over The end of your Erasmus programme might feel like the end of the world you currently live in, but the world after your Erasmus will be ev...

How a Youth Exchange Shaped My Future This might feel like a very personal piece, but above all it is meant to highlight the inspiration, skills, and self exploration that lea...

An Unbreakable Bond: ESN Members and Exchange Students What do exchange students mean to ESN members? They usually stay with us only for one semester, but their impact on our everyday lives is...

Celebrating 150 years of Harvard Summer School. Learn about our history.

Why You Should Make a Good Night’s Sleep a Priority

Poor sleep habits and sleep deprivation are serious problems for most high school and college students. This guide offers important tips on how—and why—to improve your sleep hygiene.

The time you spend in high school and college can be both fun and rewarding. At the same time, these can be some of the busiest years of your life.

Balancing all the demands on your time—a full course load, extracurricular activities, and socializing with friends—can be challenging. And if you also work or have family commitments, it can feel like there just aren’t enough hours in the day. 

With so many competing priorities, sacrificing sleep may feel like the only way to get everything done. 

Despite the sleepiness you might feel the next day, one late night probably won’t have a major impact on your well-being. But regularly short-changing yourself on quality sleep can have serious implications for school, work, and your physical and mental health.

Alternatively, prioritizing a regular sleep schedule can make these years healthier, less stressful, and more successful long-term.

The sleep you need versus the sleep you get

According to the National Sleep Foundation , high school students (ages 14-17) need about eight to 10 hours of sleep each night. For young adults (ages 18 to 25), the range is need between seven and nine hours.

How do you know how much sleep you need within this range? 

According to Dr. Edward Pace-Schott, Harvard Summer School and Harvard Medical School faculty member and sleep expert, you can answer that question simply by observing how much you sleep when you don’t need to get up.

“When you’ve been on vacation for two weeks, how are you sleeping during that second week? How long are you sleeping? If you’re sleeping eight or nine hours when you don’t have any reason to get up, then chances are you need that amount or close to that amount of sleep,” says Pace-Schott. 

Most students, however, get far less sleep than the recommended amount. 

Seventy to 96 percent of college students get less than eight hours of sleep each week night. And over half of college students sleep less than seven hours per night. The numbers are similar for high school students; 73 percent of high school students get between seven and seven and a half hours of sleep .

Of course, many students attempt to catch up on lost sleep by sleeping late on the weekends. Unfortunately, this pattern is neither healthy nor a true long-term solution to sleep deprivation. 

And what about those students who say that they function perfectly well on just a couple hours of sleep?

“There are very few individuals who are so-called short sleepers, people who really don’t need more than six hours of sleep. But, there are a lot more people who claim to be short sleepers than there are real short sleepers,” says Pace-Schott.

Consequences of sleep deprivation

The consequences of sleep deprivation are fairly well established but may still be surprising.

For example, did you know that sleep deprivation can create the same level of cognitive impairment as drinking alcohol? 

According to the CDC , staying awake for 18 hours can have the same effect as a blood alcohol content (BAC) of 0.05 percent. Staying awake for 24 hours can equate to a BAC of 0.10 percent (higher than the legal limit of 0.08 percent). 

And according to research by AAA , drowsy driving causes an average of 328,000 motor vehicle accidents each year in the US. Drivers who sleep less than five hours per night are more than five times as likely to have a crash as drivers who sleep for seven hours or more.  

Other signs of chronic sleep deprivation include:

• Daytime sleepiness and fatigue
• Irritability and short temper
• Mood changes
• Trouble coping with stress
• Difficulty focusing, concentrating, and remembering

Over the long term, chronic sleep deprivation can have a serious impact on your physical and mental health. Insufficient sleep has been linked, for example, to weight gain and obesity, cardiovascular disease, and type 2 diabetes.

The impact on your mental health can be just as serious. Harvard Medical School has conducted numerous studies, including research by Pace-Schott, demonstrating a link between sleep deprivation and mental health disorders such as anxiety and depression.

Earn college credits with a summer course at Harvard Summer School.

Importance of sleep for high school and college students

As difficult as it is to prioritize sleep, the advantages of going to bed early and getting quality sleep every night are very real.

College students who prioritize sleep are likely to see an improvement in their academic performance.

If you are well rested, you will experience less daytime sleepiness and fatigue. You may need less caffeine to stay awake during those long lectures. And you will also find you are more productive, more attentive to detail, and able to concentrate better while studying.

But the connection between sleep and academic performance goes well beyond concentration and attentiveness.

“Sleep is very important for consolidating memories. In any sort of experimental setting, study results show better performance if you learn material and then sleep on it, instead of remaining awake. So there’s lots and lots of evidence now indicating that sleep promotes memory strengthening and memory consolidation,” says Pace-Schott. 

There is also a strong connection between sleep quality and stress.

Students who prioritize sleep are better able to cope with the stress that comes with being an active student. 

“It’s a vicious circle where the more stressed you get, the less you sleep, and the less you sleep, the more stressed you get. And in the long term, that can lead to serious psychiatric problems,” says Pace-Schott.

In the worst case scenario, the combination of lack of sleep and stress can lead to mental health disorders such as depression, general anxiety disorder, and potentially even post-traumatic stress disorder.

But prioritizing sleep can create a positive feedback loop as well. 

Establishing a sleep schedule and adequate sleep duration can improve your ability to cope with stress. Being active and productive will help you get more done throughout the day, which also reduces feelings of stress.

And the less stressed you feel during the day, the better you will sleep at night. 

Tips for getting more sleep as a student

The key to getting a good night’s sleep is establishing healthy sleep habits, also known as sleep hygiene.

The first step is deciding to make sleep a priority. 

Staying ahead of coursework and avoiding distractions and procrastination while you study is key to avoiding the need for late night study sessions. And prioritizing sleep may mean leaving a party early or choosing your social engagements carefully. 

Yet the reward—feeling awake and alert the next morning—will reinforce that positive choice. 

The next step is establishing healthy bedtime and daytime patterns to promote good quality sleep.

Pace-Schott offers the following tips on steps you can take to create healthy sleep hygiene:

• Limit caffeine in close proximity to bed time. College students should also avoid alcohol intake, which disrupts quality sleep.
• Avoid electronic screens (phone, laptop, tablet, desktop) within an hour of bedtime. 
• Engage in daily physical exercise, but avoid intense exercise within two hours of bedtime.
• Establish a sleep schedule. Be as consistent as possible in your bedtime and rise time, and get exposure to morning sunlight.
• Establish a “wind-down” routine prior to bedtime.
• Limit use of bed for daily activities other than sleep (e.g., TV, work, eating)

Of course, college students living in dorms or other communal settings may find their sleep disturbed by circumstances beyond their control: a poor-quality mattress, inability to control the temperature of your bedroom, or noisy roommates, for example. 

But taking these active steps to promote healthy sleep will, barring these other uncontrollable circumstances, help you fall asleep faster, stay asleep, and get a more restorative sleep.

And for students who are still not convinced of the importance of sleep, Pace-Schott says that personal observation is the best way to see the impact of healthy sleep habits. 

“Keep a sleep diary for a week. Pay attention to your sleep in a structured way. And be sure to record how you felt during the day. This can really help you make the link between how you slept the night before and how you feel during the day. It’s amazing how much you will learn about your sleep and its impact on your life.” 

Interested in summer at Harvard? Learn more about our summer programs.

Request Information

What You Need to Know About Pre-College Program Activities

Rigorous, fast-paced—and a lot of fun.

Harvard Division of Continuing Education

The Division of Continuing Education (DCE) at Harvard University is dedicated to bringing rigorous academics and innovative teaching capabilities to those seeking to improve their lives through education. We make Harvard education accessible to lifelong learners from high school to retirement.

An official website of the United States government

The .gov means it’s official. Federal government websites often end in .gov or .mil. Before sharing sensitive information, make sure you’re on a federal government site.

The site is secure. The https:// ensures that you are connecting to the official website and that any information you provide is encrypted and transmitted securely.

• Publications
• Account settings

Preview improvements coming to the PMC website in October 2024. Learn More or Try it out now .

• Advanced Search
• Journal List
• Adv Med Educ Pract

The Effect of Sleep Quality on Students’ Academic Achievement

Rostam jalali.

1 Faculty of Nursing and Midwifery, Kermanshah University of Medical Sciences, Kermanshah, Iran

Habibollah Khazaei

2 Sleep Disorders Research Center, Kermanshah University of Medical Sciences, Kermanshah, Iran

Behnam Khaledi Paveh

Zinab hayrani, lida menati.

Sleep is an inseparable part of human health and life, which is crucial in learning, practice, as well as physical and mental health. It affects the capacity of individual learning, academic performance, and neural-behavioral functions. This study aimed to determine the relationship between sleep quality and students’ academic achievement among students at Kermanshah University of Medical Sciences.

In this cross-sectional study, 102 medical students from different fields, with maximum variation sampling, completed Pittsburgh Sleep Quality Index (PSQI). For data analysis, SPSS 19 was used through which Pearson correlation test, Spearman test, and t -test were employed.

Based on the quality of sleep questionnaire scores, the results indicated no significant difference between students with high grades and those with low grades. However, there were moderate and sometimes severe sleep disturbances in both groups.

The results showed no significant difference between sleep quality and academic achievement. Nevertheless, longitudinal study should be performed to control for confounding factors.

Sleep is an inseparable part of human health and life, and is pivotal to learning and practice as well as physical and mental health. 1 Studies have suggested that insufficient sleep, increased frequency of short-term sleep, and going to sleep late and getting up early affect the learning capacity, academic performance, and neurobehavioral functions. 2 , 3 Previous studies have indicated that the quantity of sleep reported by individuals as delayed or inappropriate sleep, waking up too late, especially at weekends and daytime sleepiness is associated with compromised academic performance in children and adults. 2 Some studies have emphasized the relationship between delayed starting time of classes and academic success. 4 Reduced overnight sleep or altered sleep patterns has been associated with severe drowsiness and failure in academic success. 5 In a study, people who had enough sleep compared to their sleep-deprived individuals used innovative solutions twice as often when confronted with complex mathematical problems. 6 The chance of academic failure was as long as one or more than 1 year in students with inadequate sleep compared to those with proper sleep. 7 People who sleep less and sleep during the day are more prone to vehicle and work accidents. 8 In some studies, sleep efficiency has been considered as essential for recovery, cognitive processing, and memory integration. 9 On the other hand, lack of sleep has been associated with emotional instability and impaired concentration. 10 In this regard, students are particularly at risk of developing sleep disorders and development of the disorder among them has a negative effect on their academic performance across different grades, 11 – 13 However, there is no consensus in this case and not all studies state that sleep disorders yield a negative effect on academic performance. Eliasson (2010) believes that the time it takes to fall asleep and waking up affect academic performance more than duration of sleep does. 14 Sweileh and colleagues (2011) also believe that there is no relationship between sleep quality and academic success. 15 Similarly, it is claimed there is no relationship between the night sleep before the exam and test scores either. 16

In another study, the author believes stress from lack of sleep causes poor school performance. 17 On the other hand, in a systematic review, the authors could not establish a cause and effect relationship between sleep quality and academic performance. 2 In their meta-analysis study, Dewald and colleagues (2010) emphasized that because of the diversity of the methodology of studies, it is impossible to definitely derive a relationship between sleep quality and academic performance, and thus more longitudinal intervention studies are warranted. 1 According to different conclusions in this respect, the researchers decided to determine the relationship between sleep quality and academic performance among students at Kermanshah University of Medical Sciences.

In this cross-sectional study, through maximum variation sampling, the first three students with highest scores and three last students with lowest scores were selected, and the Pittsburgh Sleep Quality Index (PSQI) was completed for them.

The study population consisted of students of Kermanshah University of Medical Sciences. The samples were also students at each school with the highest GPA (first three high scores) and the lowest GPA (last three lowest scores). The sampling was purposeful sampling with maximum variation. The sample covered a number of disciplines in the third semester and above ( Figures 1 & 2 ). After determining the target students, the questionnaire was given to them and then returned to the researcher after completion.

Abundant distribution of students by field of study.

Frequency distribution of students by semester.

The data collection instruments were demographic form (including age, gender, place of residence, grade, rank in the class, discipline) and Pittsburgh Sleep Quality Index (PSQI). PSQI is a self-report questionnaire which examines the quality of sleep. It has 18 questions which are classified into seven components: the first component is the subjective sleep quality which is determined with Question 9. The second component is related to delays in falling asleep, where the score is calculated by two questions, the mean score of Question 2 and part of Question 5. The third component deals with sleep duration and is determined by Question 4. The fourth component is related to the efficiency and effectiveness of sleeping in patients. Its score is calculated via dividing the total hours of sleep by total hours in the bed multiplied by 100. Then, the fifth component deals with sleep disorders and is achieved by calculating the mean value of Question 5. The sixth component is related to hypnotic drugs and is determined based on Question 6. Finally, the seventh component captures inadequate performance throughout the day and is determined by two questions (mean scores of Questions 7 and 8). Each question is rated between 0 and 3 points where maximum score for each component is 3. The total scores range of the seven components making up the total score range from 0 to 21. Higher scores represent a lower sleep quality, where a score above 6 indicates poor sleep quality. The reliability and validity of this inventory have also been approved in Iran, where the Cronbach’s alpha coefficient of the questionnaire was 0.78 to 0.82. 18 In another study, Cronbach’s alpha for the Persian version was 0.77. In cut-off point 5, the sensitivity and specificity were 94% and 72%, and in cut-off point 6, they were 85% and 84%, respectively. 19

After collecting the questionnaires and introducing students’ demographic data to a computer using SPSS version 16, the relationship between sleep quality scores and grade point average (GPA high and low) was calculated.

The results indicated that 34 cases (33.3%) of the subjects were male. The mean age of the sample 23.10 ± 3.25, where the mean age for females was 22.46± 2.44 and for males was 24.38± 4.19. The participants in the study came from various disciplines including laboratory science, medicine, pharmacology, emergency medicine, obstetrics, radiology, operating room, health technology, and nursing.

Most students lived in dormitories (50%) and 46.1% at home, with 3.9% living in rental houses. The students' educational level ranged between the third semester and twelfth semester.

Among those participating in the study, 67 patients (65.7%) consumed coffee, 90 cases (88.2%) used tea, and 1 (1%) took a drug.

For comparing the mean scores of students and the component of sleep, Spearman test (non-normal data) was employed, where a significant correlation was observed between GPA and hours taking to fall asleep ( Table 1 ).

The Relationship Between Sleep Components and GPA in KUMS Students

Similarly, there was a relationship between sleep components and tea, coffee, hypnotic drugs, and drug ( Table 2 ).

The Relationship Between Sleep Components and Type of Drink or Drug in KUMS Students Kermanshah

On the other hand, independent t -test between Pittsburgh scores in the two groups did not show any significant differences. Nevertheless, impaired sleep quality was moderate to severe in both groups ( Table 3 ).

The Difference Between the Mean Pittsburg Scores in Two Groups (Students with High and Low GPA)

The results indicated that impaired sleep quality between the two groups was not statistically significant. Although the relationship between sleeping and academic success has been introduced in medical literature since a long time, there still no definitive answer in this case. In a meta-analysis study conducted to examine the impact of sleep quality, sleep duration, and sleepiness on adolescents’ academic performance, although all three variables were related to academic achievement (positive relationship between sleep quality and duration of sleep and negative association with sleepiness), this relationship was very trivial. 1

On the other hand, another systematic review study of descriptive studies concluded that sleep disturbance adversely affects different areas such as general health, social status, and academic performance. However, longitudinal studies are required for a more accurate examination. 20 , 21 In an another systematic review of other authors, the authors concluded that under-sleeping would have an impact on learning of some students, and could have a detrimental effect on academic achievement. 22 Further, another review study also suggests a conclusive recommendation which has to be done to modify sleep so that it can be used for academic success. 23

The present study was conducted to explore whether sleep disorder can influence academic achievement or not. Accordingly, a specific sample of accomplished or unachieved students were selected to compare the quality and quantity of sleep. However, no significant difference was between the two groups. Other studies have reached similar conclusions.

Sweileh and his colleagues in a study on 400 Palestinian students concluded that academic achievement was not correlated with sleep quality. 15 In another study on 189 medical students in Pakistan, there was no significant association between lack of sleep and test scores. 16 In this regard, there is a possibility of sleep disorder in students, and this possibility has been expressed for the lack of academic achievement, but it has not been clearly explained. 11 In another study, sleepiness during the day (not the quality and quantity of sleep) was identified as an independent predictor of academic success. 5 In a similar study again the time it takes to fall sleep and the wake-up time (not the total amount of sleep) were associated with academic success, 14 where the total amount of sleep in adolescents with a dynamic mind was not related to their academic achievement. 24 In contrast to such studies that emphasize lack of association or low association, there are other studies that have observed an inverse relationship between sleep disturbance and academic achievement. In a study on 491 first-, second-, and third-year medical students, there was a correlation between academic performance and the amount of nighttime sleep as well as daytime sleepiness. 25 In a similar study on medical students, lack of sleep at night, late going to bed, and daytime sleepiness had a negative effect on the academic performance of the students. 26 Notably, sleep disturbances are likely to yield a negative impact on academic performance, thereby causing a vicious cycle. 25 , 27 Taken together, the studies suggest that most studies have mentioned poor quality sleep among the majority of students. 3 , 26 , 27 Accordingly, concluding the relationship between common sleep disturbance and academic performance should be done with caution. The reason is that academic success can be affected by different factors including the level of family income, the evolutionary process, intake of supplements and vitamins, family size, social media dependency, addiction to social networks, and social issues. In studies these extraneous factors are not under control, thus emphasizing the fact that the presence or absence of correlation between sleep quality and academic performance should be done with caution and using longitudinal studies.

Limitations

The main limitation of this study was the small sample size, but a specific sampling method was chosen to overcome this shortcoming. Another limitation of the study was not controlling for confounding factors in the study. Based on the results of this study and similar studies, further research should be conducted with a better design.

The results indicated no significant difference between sleep quality in achieved and unachieved academic performance. Nevertheless, to conclude with more certainty, longitudinal studies should be performed to control confounding factors.

Acknowledgments

The authors of this article appreciate the collaborations of the Sleep Disorders Research Center.

Funding Statement

Funding for this research was provided by the Kermanshah University of Medical Sciences, Sleep Disorders Research Center (93026).

Data Sharing Statement

The datasets used and analyzed during the current study are available from the corresponding author on reasonable request.

Ethics Approval and Consent to Participate

Informed consent obtained from all participants in the study and this study conducted by the Sleep Disorders Research Center. Identity letter obtained from deputy of research and technology to collecting data. Ethics approval was received from the ethics committee of deputy of research and technology – Kermanshah University of Medical Sciences, number 93026 on 6 April 2013.

The authors declare that they have no conflict of interest.