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Longevity Library · Lab reference

Written by Daniel Tagge, MD
Updated October 10, 2026
Reviewed October 12, 2026
35 sources · Measured in hours per night

System: Chronobiology

SleepSleep duration · Sleep regularity

Across 27 cohorts of 1.38 million adults, people who reported short sleep had a 12 percent higher risk of death and people who reported long sleep a 30 percent higher risk, with the lowest risk near 7 hours; a 2015 consensus of the American Academy of Sleep Medicine and Sleep Research Society recommends 7 or more hours on a regular basis and calls the risk above 9 hours uncertain, and in 60,977 adults wearing a recorder, how regular sleep was predicted mortality more strongly than how long it was.

Sleep is the one lever every hormone on this shelf answers to. The consensus guidance is 7 or more hours a night, the National Sleep Foundation prints 7 to 9 for adults, and the cohorts find the lowest risk near 7 with risk rising on both sides, the long side probably because illness lengthens sleep. One week of short nights lowers glucose tolerance, raises evening cortisol and drops testosterone in experiments; regular timing, morning light, caffeine before noon and a question about snoring move it more than anything in a bottle.

01 · The scale

Where the laboratory range and the evidence sit.

Lowest mortality and cardiovascular risk near 7 hours in the dose-response meta-analysis; 12 percent higher mortality with short sleep and 30 percent higher with long sleep across 27 cohorts; regularity of timing predicted mortality more strongly than duration in 60,977 adults wearing a recorder.

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  1. Consensus guidance for adults

    7 to 9 hours per night · AASM/SRS 2015; National Sleep Foundation 2015

  2. Under 7 hours: higher mortality (RR 1.12) and cardiovascular risk in cohorts

    4 to 6 hours per night · Cappuccio 2010; Yin 2017

  3. Lowest mortality and cardiovascular risk, nadir about 7

    7 to 8 hours per night · Yin 2017

  4. Within consensus; cohort risk rises per hour above 7, modestly

    8 to 9 hours per night · Watson 2015; Yin 2017

  5. Above 9 hours: higher mortality in cohorts (RR 1.30), read as a marker of illness; consensus calls the risk uncertain

    9 and above hours per night · Cappuccio 2010; Watson 2015

  • Laboratory range
  • Evidence supports
  • Guideline goal or unstudied
  • Higher risk in studies
Scale in hours per night. Duration means sleep obtained, not time in bed; most cohorts asked people rather than measuring, and the recorder-based studies are noted where they appear. Bands show where studies found something, not a recommendation for any one person.

02 · What it is

What sleep does.

Sleep is timed by two processes that run together: a homeostatic pressure that builds across the hours awake and discharges in sleep, and a circadian clock in the suprachiasmatic nucleus of the hypothalamus that gates when sleep comes. Clocks outside that nucleus, linked to energy metabolism, sit in peripheral tissues and can drift from the central one; the sleep-and-fast phase and the wake-and-feed phase separate anabolic from catabolic work, so sleep serves not only a use-dependent restorative role but enforces rest and fasting at the right phase of the day.1Grade C

Healthy sleep, in the words of the 2015 consensus, requires adequate duration, good quality, appropriate timing and regularity, and the absence of sleep disturbances or disorders. Duration is the most studied of these. Sleeping less than 7 hours a night on a regular basis is associated in that statement with weight gain and obesity, diabetes, hypertension, heart disease and stroke, depression, impaired immune function, pain, errors and accidents, and a higher risk of death.2Grade A

Regularity has its own measure. The Sleep Regularity Index scores the day-to-day consistency of sleep and wake timing from a wrist recorder; in 60,977 UK Biobank adults with a mean age of about 63, the median score was 81, and higher scores went with lower mortality independent of how long people slept.3Grade B

03 · Origins

Where it came from, and where it sits in the network.

Sleep is older than brains. A sleep-like state, with nighttime quiescence that reverses quickly, a slowed response to stimulation and a rebound after deprivation, has been shown in the upside-down jellyfish Cassiopea, a cnidarian with a nerve net and no central nervous system, which supports the reading that sleep arose early in animal evolution, before centralized nervous systems, and has been kept by every animal studied since, from flies and worms to vertebrates. Why it was kept is still argued, and the candidates are hypotheses rather than settled fact: the synaptic homeostasis hypothesis holds that sleep is the price the brain pays for plasticity, renormalizing the connections strengthened during waking; the glymphatic reading rests on mouse experiments in which the brain's interstitial space expanded by 60 percent during sleep and cleared beta-amyloid faster; and the two-process model's authors add that sleep also enforces rest and fasting at the phase of the day when peripheral tissues are built to do anabolic work.4,5,6,1Grade C

How humans slept before electricity is a question with data. Wrist recorders on three pre-industrial groups, the Hadza of northern Tanzania, the Kalahari San and the Tsimané of Bolivia, found sleep periods of 6.9 to 8.5 hours containing 5.7 to 7.1 hours of sleep, near the low end of industrial societies; sleep began on average 3.3 hours after sunset and ended before sunrise, ran about an hour longer in winter than in summer, tracked the night's falling temperature more than the light, and was not interrupted by extended waking. Two of the groups have no word for insomnia; when the concept was explained, 5 percent said they sometimes had trouble falling asleep and 9 percent trouble staying asleep, and fewer than a third of those had it regularly, against the 10 to 30 percent chronic insomnia the authors cite for industrial societies. Morning light exposure was the day's highest, and naps were recorded on fewer than 7 percent of winter days and fewer than 22 percent of summer days. The historian Roger Ekirch has argued from early modern records that Western Europeans slept in two intervals bridged by an hour or more of quiet wakefulness; the field study's authors read their equatorial data as evidence that any such pattern was a consequence of long winter nights at high latitude rather than the human default, and Ekirch replied in the same journal. The entry reports the dispute, not its resolution.7,8Grade C

Sleep sits upstream of most of the numbers on this shelf. Six nights of 4 hours in bed lowered glucose tolerance and thyrotropin, raised evening cortisol and increased sympathetic activity in healthy young men; a week of 5-hour nights lowered daytime testosterone 10 to 15 percent; ten nights of 4.2 hours raised C-reactive protein and heart rate, and 88 hours awake raised C-reactive protein and systolic blood pressure; three weeks of 5.6 hours a day on a 28-hour schedule cut insulin secretion after a meal by 32 percent and resting metabolic rate by 8 percent; and in 80 short sleepers with overweight, adding about 1.2 hours of sleep a night cut energy intake by about 270 kilocalories a day. Fasting insulin, fasting glucose, hemoglobin A1c, cortisol, testosterone, hs-CRP and TSH each have an entry here, and sleep is a lever on every one of them.9,10,11,12,13Grade B

04 · The usual guidance

What the guidelines say.

7 or more hours a night on a regular basis by the AASM and Sleep Research Society consensus; 7 to 9 hours for adults and 7 to 8 for older adults in the National Sleep Foundation ranges.

The 2015 joint consensus of the American Academy of Sleep Medicine and the Sleep Research Society, reached by a modified RAND appropriateness process, states that adults should sleep 7 or more hours per night on a regular basis to promote optimal health, that sleeping less than 7 hours on a regular basis is associated with adverse outcomes, and that sleeping more than 9 hours on a regular basis may be appropriate for young adults, people recovering from sleep debt and people with illnesses, while for others it is uncertain whether more than 9 hours carries a health risk. The recommendation applies to adults aged 18 to 60, and the panel notes that individual need varies with genetic, behavioral, medical and environmental factors.2Grade A

The National Sleep Foundation's 18-member panel, using the same appropriateness method, set 7 to 9 hours for young adults and adults and 7 to 8 hours for older adults, for healthy people without a sleep disorder. The panel wrote that durations outside the range may be appropriate but that deviating far from it is rare, and that people who habitually sleep outside it may be showing signs of a health problem or compromising their health.14Grade A

05 · The evidence

What the studies support.

Pooling 16 prospective studies with 27 cohort samples, 1,382,999 adults followed 4 to 25 years and 112,566 deaths, short sleep carried a 12 percent higher risk of death (relative risk 1.12, 95 percent confidence interval 1.06 to 1.18) and long sleep a 30 percent higher risk (1.30, 1.22 to 1.38), with heterogeneity between studies and no sign of publication bias. Sleep was assessed by questionnaire in every study. The long-sleep signal is the larger, and it is the one most often read as reverse causation: illness that lengthens sleep before it shortens life, which a questionnaire at baseline cannot separate from sleep itself.15Grade A

A dose-response meta-analysis of prospective cohorts published through 2016 found U-shaped associations for mortality, cardiovascular disease, coronary disease and stroke, with the lowest risk at about 7 hours and little difference by sex. Below 7 hours, each hour less carried a pooled 6 percent higher mortality (1.06, 1.04 to 1.07); above 7, each hour more carried 13 percent (1.13, 1.11 to 1.15). For total cardiovascular disease the figures were 6 and 12 percent per hour, for coronary disease 7 and 5 percent, and for stroke 5 and 18 percent, the long side again steeper than the short.16Grade A

Regularity was tested against duration in 60,977 UK Biobank participants, mean age 62.8, who wore a wrist accelerometer for more than 10 million hours in total and were followed a mean of 6.3 years, with 1,859 deaths. Compared with the least regular fifth, the four more regular fifths had 20 to 48 percent lower all-cause mortality, 16 to 39 percent lower cancer mortality and 22 to 57 percent lower cardiometabolic mortality after adjustment for age, sex, ethnicity, sociodemographic, lifestyle and health factors, and the regularity index predicted mortality better than sleep duration did in matched and nested models. A systematic review of 41 studies and 92,340 adults from 14 countries found later timing and greater night-to-night variability generally associated with worse health, social jet lag associated with worse health, and no threshold for how late or how variable is too much; the quality of that evidence ran from very low to moderate.3,17Grade B

The experiments are small, controlled and consistent. Eleven healthy young men restricted to 4 hours in bed for six nights had lower glucose tolerance, lower thyrotropin, raised evening cortisol and higher sympathetic activity than after six nights of 12 hours in bed, changes the authors compared with normal aging. Twenty-four healthy adults who spent more than five weeks in a laboratory, three of them sleeping 5.6 hours per 24 on a 28-hour day that forced the clock out of alignment, had an 8 percent lower resting metabolic rate, 8 percent higher fasting glucose and a 14 percent higher glucose peak after a standard breakfast, because insulin secretion fell by 32 percent; 3 of 21 reached prediabetic post-meal levels, young and older alike, and everything normalized over nine days of recovery sleep.9,12Grade B

Extending sleep changes behavior without a diet. Eighty adults aged 21 to 40 with overweight who habitually slept less than 6.5 hours were randomized to one counseling session aimed at an 8.5-hour bedtime or to their usual sleep; the extension group slept about 1.2 hours more a night by wrist recorder and ate about 270 fewer kilocalories a day (95 percent confidence interval 147 to 393 fewer), measured by doubly labeled water rather than diaries, with no change in energy expenditure and a resulting negative energy balance over two weeks. The longer a person's sleep grew, the more intake fell (r = minus 0.41).13Grade B

Hormones and inflammation follow the same direction. Ten healthy men who slept 5 hours a night for one week had daytime testosterone 10 to 15 percent lower than after 10-hour nights (16.5 versus 18.4 nmol/L), a drop the authors set against the 1 to 2 percent a year of normal aging, with lower vigor and no rise in cortisol. In two experiments of 10 people each, 88 hours awake and ten nights of 4.2 hours both raised high-sensitivity C-reactive protein, with systolic blood pressure rising in the first and heart rate in the second. Across 72 observational and experimental studies of more than 50,000 people, sleep disturbance and long sleep were associated with higher C-reactive protein and interleukin-6, short sleep weakly with C-reactive protein alone, and experimental deprivation with neither: the inflammatory signal belongs to chronically poor and long sleepers in the population more than to a few short nights in a laboratory.10,11,18Grade B

Sleep apnea is the hidden cause behind many short, broken or unrefreshing nights, and it is common: a literature-based estimate across 16 countries put 936 million adults aged 30 to 69 at mild to severe obstructive sleep apnea and 425 million at moderate to severe. In 709 adults of the Wisconsin Sleep Cohort studied by overnight polysomnography, the odds of hypertension four years later rose with the baseline apnea-hypopnea index, 1.42 at 0.1 to 4.9 events an hour, 2.03 at 5 to 14.9 and 2.89 at 15 or more, independent of body mass, neck and waist size, age, sex, alcohol and smoking. In 3,542 Olmsted County adults referred for a sleep study and followed 4.7 years, apnea doubled the unadjusted hazard of new atrial fibrillation (2.18), and in those under 65 the depth of nighttime oxygen desaturation predicted it independently of obesity.19,20,21Grade B

Treating apnea has not yet been shown to prevent cardiovascular events in people who already have cardiovascular disease. In the SAVE trial, 2,717 adults aged 45 to 75 with moderate to severe apnea and coronary or cerebrovascular disease, most of them not sleepy, were randomized to CPAP plus usual care or usual care alone; after a mean of 3.7 years the primary composite of cardiovascular death, heart attack, stroke and related admissions occurred in 17.0 percent with CPAP and 15.4 percent without (hazard ratio 1.10, 0.91 to 1.32), while CPAP reduced snoring and daytime sleepiness and improved quality of life and mood. Mean use was 3.3 hours a night. The result argues for treating apnea because of how people feel and function, and for honesty about what it has been proved to prevent.22Grade B

Timing preference and naps carry smaller signals. In 433,268 UK Biobank adults aged 38 to 73 followed 6.5 years, definite evening types had a 10 percent higher all-cause mortality than definite morning types (hazard ratio 1.10, 1.02 to 1.18) and higher odds of diabetes (1.30) and psychological disorders (1.94), from a single self-reported question and after adjustment for sleep duration; the authors read it as misalignment between internal timing and imposed schedules rather than evening preference itself. Across 11 cohorts of 151,588 people, naps of 60 minutes or more a day went with 82 percent higher cardiovascular disease and 27 percent higher mortality compared with not napping, naps under 60 minutes with neither, and the dose-response curve was lowest at 0 to 30 minutes; long naps, like long nights, may mark illness and apnea as much as cause harm.23,24Grade B

06 · What moves it

The levers with evidence behind them.

What is listed here has been tested. The size of each effect, and the size of the study, are in the sentence, so a small effect reads as a small effect.

  • Light, by the clock

    morning light advances the clock and evening light delays it; screens at night delay sleep and the clock

    The human clock answers to light differently by hour. In 21 healthy adults studied under constant conditions, a 6.7-hour exposure to about 10,000 lux shifted melatonin timing along a phase response curve with a peak-to-trough span of 5.02 hours: light before the core body temperature minimum, in the evening and early night, delayed the clock, light after it, in the morning, advanced it, and there was no dead zone during the day. Reading on a light-emitting device in the hours before bed, compared with a printed book in the same people, lengthened the time to fall asleep, suppressed melatonin, delayed the circadian clock, reduced and delayed REM sleep and lowered alertness the next morning; in a survey of 1,508 American adults, 90 percent used some electronic device within an hour of bedtime at least a few nights a week.25,26Grade C

  • Caffeine

    a late dose shortens and fragments sleep, even six hours before bed

    Caffeine's half-life is about 3 to 6 hours, with blood levels peaking 30 to 120 minutes after a dose. In a placebo-controlled home study, 400 mg of caffeine taken at bedtime, 3 hours before bed or 6 hours before bed each disturbed sleep by self-report and by a portable monitor, and the loss of total sleep time from the 6-hour dose was large enough that the authors recommend no substantial caffeine for at least 6 hours before bed. A dose at 4 in the afternoon is still at work at 10 at night.27,28Grade C

  • Alcohol

    shortens the time to fall asleep and breaks the second half of the night

    A qualitative review of every published study of alcohol in healthy volunteers found that at all doses it shortens the time to fall asleep, consolidates the first half of the night and increases disruption in the second half; it delays the first REM period at all doses, reduces total REM at moderate and high doses, and increases slow-wave sleep in the first half of the night. The nightcap buys an easier start and a worse finish.29Grade C

  • Exercise

    lengthens and consolidates sleep, modestly, whatever the intensity

    Across 66 studies published through May 2013, a single bout of exercise had small benefits on total sleep time, time to fall asleep, sleep efficiency and slow-wave sleep and a moderate benefit on time awake after sleep onset; regular exercise had small benefits on total sleep time and efficiency, small to medium on time to fall asleep and moderate on sleep quality. Effects varied by sex, age, baseline fitness, type, time of day and adherence, and not by intensity or whether the exercise was aerobic.30Grade B

  • Shift work and the misaligned clock

    shortens sleep, impairs glucose handling and, over years, raises coronary risk

    In 189,158 initially healthy nurses followed 24 years, 10 or more years of rotating night shift work carried an 18 percent higher coronary heart disease risk in the older cohort (1.18, 1.10 to 1.26) and 15 percent in the younger (1.15, 1.01 to 1.32), a statistically significant but small absolute increase that waned with time since quitting. In 2019 an IARC working group of 27 experts from 16 countries classified night shift work as probably carcinogenic to humans (Group 2A), on sufficient evidence in experimental animals, strong mechanistic evidence and limited evidence from human studies. The laboratory version of shift work, 5.6 hours of sleep on a 28-hour day for three weeks, cut insulin secretion by 32 percent.31,32,33,12Grade B

  • Sleep apnea

    fragments sleep and drives blood pressure, atrial fibrillation and daytime sleepiness; a treatable cause

    An apnea-hypopnea index of 15 or more events an hour nearly tripled the odds of hypertension four years later in the Wisconsin cohort, and the depth of nighttime oxygen desaturation predicted new atrial fibrillation in adults under 65. Treatment in the SAVE trial reduced snoring and sleepiness and improved mood and quality of life without preventing cardiovascular events over 3.7 years. Testing is the step that matters: no amount of sleep hygiene lengthens a night that is being interrupted by a closed airway.20,21,22Grade B

  • Treatment for insomnia

    cognitive behavioral therapy for insomnia is the guideline's first-line treatment; medication is a short-term, shared decision

    The American College of Physicians recommends that all adults with chronic insomnia disorder receive cognitive behavioral therapy for insomnia as the initial treatment (a strong recommendation on moderate-quality evidence), and that clinicians use shared decision-making, including the benefits, harms and costs of short-term medication, to decide whether to add a drug when the therapy alone has not worked. This page does not rank sleeping medications; it reports the guideline's order of operations.34Grade A

07 · Reading it well

Caveats, and what belongs with a physician.

Nearly all of the mortality evidence is self-reported sleep. Every one of the 16 studies in the 2010 meta-analysis assessed duration by questionnaire, and in the 2020 review of timing and regularity only 37 percent of studies measured sleep objectively. People misjudge their own sleep, and the recorder-based cohorts, which can score regularity at all, are a different and better instrument.15,17Grade B

Consumer wearables detect sleep well and wake poorly, and their stage reports are not reliable. Against polysomnography across three nights in 34 healthy young adults, seven consumer devices had sensitivity for sleep of 0.93 or higher but specificity for wake of only 0.18 to 0.54, mixed agreement on sleep stages, and worse performance on disrupted nights. Total sleep time and timing from a wearable are usable; a deep-sleep or REM percentage is not a measurement to act on.35Grade C

Long sleep is more often a sign than a cause. The consensus statement allows that more than 9 hours may be appropriate for people recovering from sleep debt and people with illnesses; in the pooled studies, long sleep rather than short was associated with higher C-reactive protein and interleukin-6; and the National Sleep Foundation panel reads habitual sleep outside its range as a possible sign of a health problem. A person who newly needs 10 hours has a question to answer, not a habit to trim.2,18,14Grade B

The experiments that make sleep look causal are small, short and done in young, healthy volunteers: 11 men for six nights, 10 men for a week, 24 adults for five weeks. They show the direction and the mechanism, and the cohorts show the association at scale; no large trial has yet shown that lengthening or regularizing sleep in a healthy adult changes a hard outcome.9,10,12Grade C

See a physician

  • Loud snoring with pauses in breathing that someone else has witnessed, or waking gasping, or daytime sleepiness that intrudes on reading, meetings or conversation, especially with high blood pressure or atrial fibrillation; this is a sleep study, not a supplement.
  • Ever falling asleep at the wheel or fighting to stay awake while driving.
  • Trouble falling or staying asleep on most nights for more than three months, with daytime consequences; chronic insomnia has a first-line treatment, and it is not a pill.
  • A change in sleep that arrives with a change in mood: sleeping far more or far less than usual alongside low mood, loss of interest, anxiety or racing thoughts.
  • Newly needing much more sleep than before, or long sleep that leaves you unrefreshed, which can be the first sign of a medical illness.
  • Acting out dreams, violent movements in sleep, or an irresistible urge to move the legs at night.

This page is education, not individual medical advice, and reading it creates no physician-patient relationship.

08 · Open questions

What the literature does not settle.

  • No study tells an individual their own number. The consensus floor of 7 hours and the cohort nadir near 7 are population averages; individual need varies with genetics, age, illness and season, and the only test available is how a person functions on a regular schedule.
  • Whether extending sleep changes hard outcomes is untested. The randomized evidence stops at energy intake, glucose handling and hormones over days to weeks; no trial has lengthened or regularized sleep in healthy adults and counted heart attacks, cancers or deaths.
  • How much of the long-sleep risk is illness and how much is sleep remains unresolved, and the cohorts, built on questionnaires, cannot separate the two.
  • Regularity outperformed duration in one large recorder-based cohort; whether a regular schedule is a cause of longer life or a marker of a stable, healthy life is not yet known.
  • Whether treating sleep apnea prevents cardiovascular events in people who do not yet have cardiovascular disease, or in those who are sleepy and use treatment for more than the 3.3 hours a night seen in SAVE, is an open trial question.
  • Consumer wearables are improving faster than their validation; which device, in which population, under which firmware, measures what it claims is not settled, and the companies' own material is not evidence.

10

Questions

11 · Sources

35 sources, read in full.

Numbered in the order they appear. Each line says what this page relies on from the paper; the link opens the record at PubMed or the publisher.

  1. 1.

    Borbély AA, Daan S, Wirz-Justice A, Deboer T. The two-process model of sleep regulation: a reappraisal. Journal of Sleep Research. 2016. PMID 26762182. DOI 10.1111/jsr.12371.

    Review · A homeostatic Process S interacts with a circadian Process C from the suprachiasmatic nuclei; peripheral oscillators tied to energy metabolism can dissociate from it; the sleep/fast and wake/feed phases segregate anabolic and catabolic processes, so sleep also enforces rest and fasting at the right phase.

  2. 2.

    Watson NF, Badr MS, Belenky G, et al.. Recommended Amount of Sleep for a Healthy Adult: A Joint Consensus Statement of the American Academy of Sleep Medicine and Sleep Research Society. Sleep. 2015. PMID 26039963. DOI 10.5665/sleep.4716.

    Consensus statement · Adults should sleep 7 or more hours per night on a regular basis; less than 7 is associated with adverse outcomes; more than 9 may be appropriate for young adults, people recovering from sleep debt and people with illnesses, and is of uncertain risk for others; healthy sleep requires adequate duration, quality, timing, regularity and absence of disorders.

  3. 3.

    Windred DP, Burns AC, Lane JM, et al.. Sleep regularity is a stronger predictor of mortality risk than sleep duration: A prospective cohort study. Sleep. 2024. PMID 37738616. DOI 10.1093/sleep/zsad253.

    Prospective cohort · In 60,977 UK Biobank adults with accelerometer-derived Sleep Regularity Index scores and 1,859 deaths over a mean 6.3 years, the four more regular quintiles had 20 to 48 percent lower all-cause mortality than the least regular; regularity predicted mortality more strongly than duration.

  4. 4.

    Nath RD, Bedbrook CN, Abrams MJ, et al.. The Jellyfish Cassiopea Exhibits a Sleep-like State. Current Biology. 2017. PMID 28943083. DOI 10.1016/j.cub.2017.08.014.

    Laboratory method study · The cnidarian Cassiopea shows rapidly reversible nighttime quiescence, a delayed response to stimulation and a rebound after deprivation, supporting the hypothesis that sleep arose early in animal evolution, before a centralized nervous system.

  5. 5.

    Tononi G, Cirelli C. Sleep and the price of plasticity: from synaptic and cellular homeostasis to memory consolidation and integration. Neuron. 2014. PMID 24411729. DOI 10.1016/j.neuron.2013.12.025.

    Review · The synaptic homeostasis hypothesis: sleep is the price the brain pays for plasticity, renormalizing net synaptic strength and restoring cellular homeostasis after the strengthening of waking; stated as a hypothesis with open issues.

  6. 6.

    Xie L, Kang H, Xu Q, et al.. Sleep drives metabolite clearance from the adult brain. Science. 2013. PMID 24136970. DOI 10.1126/science.1241224.

    Laboratory method study · In live mice, natural sleep or anesthesia increased the brain's interstitial space by 60 percent and the convective exchange of cerebrospinal and interstitial fluid, raising the clearance rate of beta-amyloid.

  7. 7.

    Yetish G, Kaplan H, Gurven M, et al.. Natural sleep and its seasonal variations in three pre-industrial societies. Current Biology. 2015. PMID 26480842. DOI 10.1016/j.cub.2015.09.046.

    Cross-sectional study · Hadza, San and Tsimané adults slept 5.7 to 7.1 hours within 6.9 to 8.5-hour sleep periods beginning 3.3 hours after sunset, about an hour longer in winter, without extended night waking; two groups have no word for insomnia and 1.5 to 2.5 percent reported it regularly; naps on under 7 percent of winter and 22 percent of summer days.

  8. 8.

    Ekirch AR. Segmented Sleep in Preindustrial Societies. Sleep. 2016. PMID 26888454. DOI 10.5665/sleep.5558.

    Review · A historian's letter replying to the three-society field study, restating the case from early modern records for a segmented night of two sleeps; the letter's body could not be read, and the entry reports the dispute without a verdict.

  9. 9.

    Spiegel K, Leproult R, Van Cauter E. Impact of sleep debt on metabolic and endocrine function. Lancet. 1999. PMID 10543671. DOI 10.1016/S0140-6736(99)01376-8.

    Randomized trial · In 11 young men restricted to 4 hours in bed for six nights versus 12 hours, glucose tolerance and thyrotropin were lower, evening cortisol was raised and sympathetic activity higher; the authors compared the changes with normal aging.

  10. 10.

    Leproult R, Van Cauter E. Effect of 1 week of sleep restriction on testosterone levels in young healthy men. JAMA. 2011. PMID 21632481. DOI 10.1001/jama.2011.710.

    Randomized trial · In 10 healthy young men, one week of 5-hour nights lowered daytime testosterone by 10 to 15 percent (16.5 versus 18.4 nmol/L) with lower vigor and no change in cortisol; normal aging lowers it 1 to 2 percent a year.

  11. 11.

    Meier-Ewert HK, Ridker PM, Rifai N, et al.. Effect of sleep loss on C-reactive protein, an inflammatory marker of cardiovascular risk. Journal of the American College of Cardiology. 2004. PMID 14975482. DOI 10.1016/j.jacc.2003.07.050.

    Randomized trial · In two experiments of 10 people each, 88 hours awake and ten nights of 4.2 hours both raised high-sensitivity CRP; systolic blood pressure rose in the first and heart rate in the second.

  12. 12.

    Buxton OM, Cain SW, O'Connor SP, et al.. Adverse metabolic consequences in humans of prolonged sleep restriction combined with circadian disruption. Science Translational Medicine. 2012. PMID 22496545. DOI 10.1126/scitranslmed.3003200.

    Randomized trial · 24 healthy adults, more than five weeks in the laboratory, three weeks at 5.6 hours of sleep per 24 on 28-hour days: resting metabolic rate fell 8 percent, fasting glucose rose 8 percent and the post-meal peak 14 percent, insulin secretion fell 32 percent, 3 of 21 reached prediabetic post-meal levels; all normalized in nine recovery days.

  13. 13.

    Tasali E, Wroblewski K, Kahn E, Kilkus J, Schoeller DA. Effect of Sleep Extension on Objectively Assessed Energy Intake Among Adults With Overweight in Real-life Settings: A Randomized Clinical Trial. JAMA Internal Medicine. 2022. PMID 35129580. DOI 10.1001/jamainternmed.2021.8098.

    Randomized trial · 80 adults aged 21 to 40 with overweight sleeping under 6.5 hours: one counseling session extended sleep by about 1.2 hours a night and cut energy intake by 270 kcal a day (95 percent CI 147 to 393) by doubly labeled water, with no change in expenditure.

  14. 14.

    Hirshkowitz M, Whiton K, Albert SM, et al.. National Sleep Foundation's sleep time duration recommendations: methodology and results summary. Sleep Health. 2015. PMID 29073412. DOI 10.1016/j.sleh.2014.12.010.

    Consensus statement · An 18-member panel set 7 to 9 hours for young adults and adults and 7 to 8 for older adults; durations outside the range may be appropriate but deviating far from it is rare and may signal a health problem.

  15. 15.

    Cappuccio FP, D'Elia L, Strazzullo P, Miller MA. Sleep duration and all-cause mortality: a systematic review and meta-analysis of prospective studies. Sleep. 2010. PMID 20469800. DOI 10.1093/sleep/33.5.585.

    Systematic review and meta-analysis · 16 studies, 27 cohorts, 1,382,999 participants, 112,566 deaths: short sleep RR 1.12 (1.06 to 1.18), long sleep RR 1.30 (1.22 to 1.38); sleep assessed by questionnaire throughout.

  16. 16.

    Yin J, Jin X, Shan Z, et al.. Relationship of Sleep Duration With All-Cause Mortality and Cardiovascular Events: A Systematic Review and Dose-Response Meta-Analysis of Prospective Cohort Studies. Journal of the American Heart Association. 2017. PMID 28889101. DOI 10.1161/JAHA.117.005947.

    Systematic review and meta-analysis · U-shaped associations with lowest risk at about 7 hours; mortality RR 1.06 per hour below 7 and 1.13 per hour above; cardiovascular disease 1.06 and 1.12; coronary disease 1.07 and 1.05; stroke 1.05 and 1.18.

  17. 17.

    Chaput JP, Dutil C, Featherstone R, et al.. Sleep timing, sleep consistency, and health in adults: a systematic review. Applied Physiology, Nutrition, and Metabolism. 2020. PMID 33054339. DOI 10.1139/apnm-2020-0032.

    Review · 41 articles, 92,340 adults, 14 countries: later timing and greater variability generally associated with adverse outcomes, social jet lag with worse health; no thresholds identifiable; 37 percent of studies measured sleep objectively; evidence very low to moderate quality.

  18. 18.

    Irwin MR, Olmstead R, Carroll JE. Sleep Disturbance, Sleep Duration, and Inflammation: A Systematic Review and Meta-Analysis of Cohort Studies and Experimental Sleep Deprivation. Biological Psychiatry. 2016. PMID 26140821. DOI 10.1016/j.biopsych.2015.05.014.

    Systematic review and meta-analysis · 72 studies, more than 50,000 people: sleep disturbance (CRP effect size 0.12, IL-6 0.20) and long sleep (CRP 0.17, IL-6 0.11) were associated with higher inflammation, short sleep weakly with CRP (0.09), and experimental deprivation with none.

  19. 19.

    Benjafield AV, Ayas NT, Eastwood PR, et al.. Estimation of the global prevalence and burden of obstructive sleep apnoea: a literature-based analysis. Lancet Respiratory Medicine. 2019. PMID 31300334. DOI 10.1016/S2213-2600(19)30198-5.

    Review · From 17 studies in 16 countries, an estimated 936 million adults aged 30 to 69 have mild to severe and 425 million moderate to severe obstructive sleep apnea; funded by a device manufacturer.

  20. 20.

    Peppard PE, Young T, Palta M, Skatrud J. Prospective study of the association between sleep-disordered breathing and hypertension. New England Journal of Medicine. 2000. PMID 10805822. DOI 10.1056/NEJM200005113421901.

    Prospective cohort · In 709 Wisconsin Sleep Cohort adults with polysomnography, odds of hypertension four years later were 1.42, 2.03 and 2.89 at baseline apnea-hypopnea indices of 0.1 to 4.9, 5 to 14.9 and 15 or more, independent of body habitus, age, sex, alcohol and smoking.

  21. 21.

    Gami AS, Hodge DO, Herges RM, et al.. Obstructive sleep apnea, obesity, and the risk of incident atrial fibrillation. Journal of the American College of Cardiology. 2007. PMID 17276180. DOI 10.1016/j.jacc.2006.08.060.

    Prospective cohort · In 3,542 adults referred for polysomnography and followed 4.7 years, obstructive sleep apnea predicted new atrial fibrillation (univariate HR 2.18); under 65, nocturnal oxygen desaturation (HR 3.29 per 0.5 log unit) and body mass index were independent predictors.

  22. 22.

    McEvoy RD, Antic NA, Heeley E, et al.. CPAP for Prevention of Cardiovascular Events in Obstructive Sleep Apnea. New England Journal of Medicine. 2016. PMID 27571048. DOI 10.1056/NEJMoa1606599.

    Randomized trial · In 2,717 adults with moderate to severe apnea and cardiovascular disease, CPAP (mean 3.3 hours a night) did not reduce the primary cardiovascular composite over 3.7 years (17.0 versus 15.4 percent, HR 1.10) but reduced snoring and sleepiness and improved quality of life and mood.

  23. 23.

    Knutson KL, von Schantz M. Associations between chronotype, morbidity and mortality in the UK Biobank cohort. Chronobiology International. 2018. PMID 29642757. DOI 10.1080/07420528.2018.1454458.

    Prospective cohort · In 433,268 adults aged 38 to 73 followed 6.5 years, definite evening types had HR 1.10 (1.02 to 1.18) for all-cause mortality versus definite morning types, and higher odds of diabetes (1.30) and psychological disorders (1.94), adjusted for sleep duration.

  24. 24.

    Yamada T, Hara K, Shojima N, Yamauchi T, Kadowaki T. Daytime Napping and the Risk of Cardiovascular Disease and All-Cause Mortality: A Prospective Study and Dose-Response Meta-Analysis. Sleep. 2015. PMID 26158892. DOI 10.5665/sleep.5246.

    Systematic review and meta-analysis · Across 11 cohorts and 151,588 people, naps of 60 minutes or more a day went with RR 1.82 for cardiovascular disease and 1.27 for mortality versus no nap; naps under 60 minutes with neither; J-curve lowest at 0 to 30 minutes.

  25. 25.

    Khalsa SB, Jewett ME, Cajochen C, Czeisler CA. A phase response curve to single bright light pulses in human subjects. Journal of Physiology. 2003. PMID 12717008. DOI 10.1113/jphysiol.2003.040477.

    Laboratory method study · In 21 healthy adults, a 6.7-hour bright light pulse (about 10,000 lux) produced a phase response curve with a 5.02-hour peak-to-trough span: delays before the core body temperature minimum, advances after it, and no dead zone during the day.

  26. 26.

    Chang AM, Aeschbach D, Duffy JF, Czeisler CA. Evening use of light-emitting eReaders negatively affects sleep, circadian timing, and next-morning alertness. Proceedings of the National Academy of Sciences of the United States of America. 2015. PMID 25535358. DOI 10.1073/pnas.1418490112.

    Randomized trial · Reading a light-emitting e-book before bed, versus a printed book, lengthened time to fall asleep, suppressed melatonin, delayed the circadian clock, reduced and delayed REM sleep and lowered next-morning alertness; 90 percent of 1,508 surveyed Americans used electronics within an hour of bedtime.

  27. 27.

    Mort JR, Kruse HR. Timing of blood pressure measurement related to caffeine consumption. Annals of Pharmacotherapy. 2008. PMID 18094346. DOI 10.1345/aph.1K337.

    Review · Caffeine levels peak 30 to 120 minutes after oral intake and its half-life is 3 to 6 hours.

  28. 28.

    Drake C, Roehrs T, Shambroom J, Roth T. Caffeine effects on sleep taken 0, 3, or 6 hours before going to bed. Journal of Clinical Sleep Medicine. 2013. PMID 24235903. DOI 10.5664/jcsm.3170.

    Randomized trial · 400 mg of caffeine at bedtime, 3 hours before or 6 hours before bed each disturbed sleep versus placebo by self-report and portable monitor; the authors recommend no substantial caffeine for at least 6 hours before bed.

  29. 29.

    Ebrahim IO, Shapiro CM, Williams AJ, Fenwick PB. Alcohol and sleep I: effects on normal sleep. Alcoholism: Clinical and Experimental Research. 2013. PMID 23347102. DOI 10.1111/acer.12006.

    Review · At all doses alcohol shortens sleep onset, consolidates the first half of the night and disrupts the second; it delays the first REM period at all doses, reduces total REM at moderate and high doses, and increases slow-wave sleep in the first half.

  30. 30.

    Kredlow MA, Capozzoli MC, Hearon BA, Calkins AW, Otto MW. The effects of physical activity on sleep: a meta-analytic review. Journal of Behavioral Medicine. 2015. PMID 25596964. DOI 10.1007/s10865-015-9617-6.

    Systematic review and meta-analysis · Across 66 studies, acute exercise had small benefits on total sleep time, onset latency, efficiency and slow-wave sleep and a moderate benefit on wake after sleep onset; regular exercise had small to moderate benefits on duration, latency, efficiency and quality, not moderated by intensity.

  31. 31.

    Vetter C, Devore EE, Wegrzyn LR, et al.. Association Between Rotating Night Shift Work and Risk of Coronary Heart Disease Among Women. JAMA. 2016. PMID 27115377. DOI 10.1001/jama.2016.4454.

    Prospective cohort · In 189,158 nurses followed 24 years, 10 or more years of rotating night shifts carried HR 1.18 (1.10 to 1.26) for coronary heart disease in NHS and 1.15 (1.01 to 1.32) in NHS2, a small absolute increase that waned with time since quitting.

  32. 32.

    IARC Monographs Vol 124 group. Carcinogenicity of night shift work. Lancet Oncology. 2019. PMID 31281097. DOI 10.1016/S1470-2045(19)30455-3.

    Consensus statement · The IARC Monographs working group's summary evaluation of night shift work, published July 2019; its classification wording is quoted here through Erren 2019 because the summary carries no abstract.

  33. 33.

    Erren TC, Morfeld P, Groß JV, et al.. IARC 2019: "Night shift work" is probably carcinogenic: What about disturbed chronobiology in all walks of life?. Journal of Occupational Medicine and Toxicology. 2019. PMID 31798667. DOI 10.1186/s12995-019-0249-6.

    Review · Reports that in June 2019 an IARC working group of 27 experts from 16 countries classified night shift work as probably carcinogenic to humans (Group 2A), on sufficient evidence in experimental animals, strong mechanistic evidence and limited human evidence, the same weakest stream as in 2007.

  34. 34.

    Qaseem A, Kansagara D, Forciea MA, Cooke M, Denberg TD. Management of Chronic Insomnia Disorder in Adults: A Clinical Practice Guideline From the American College of Physicians. Annals of Internal Medicine. 2016. PMID 27136449. DOI 10.7326/M15-2175.

    Guideline · Cognitive behavioral therapy for insomnia as the initial treatment for chronic insomnia disorder (strong recommendation, moderate-quality evidence); shared decision-making about short-term medication when it alone is unsuccessful.

  35. 35.

    Chinoy ED, Cuellar JA, Huwa KE, et al.. Performance of seven consumer sleep-tracking devices compared with polysomnography. Sleep. 2021. PMID 33378539. DOI 10.1093/sleep/zsaa291.

    Laboratory method study · In 34 healthy young adults over three nights, seven consumer devices had epoch sensitivity of 0.93 or higher for sleep, specificity of 0.18 to 0.54 for wake, mixed sleep-stage agreement, and worse performance on disrupted nights.

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