What does the research show about sleep duration?

Sleep duration

Cohort meta-analyses of millions of adults link both short and long sleep to more deaths, heart disease and type 2 diabetes, with the lowest risk near 7 hours. Short sleep is also linked to obesity and depression. In trials, sleep loss raised food intake, lowered insulin sensitivity, mood and attention. Extension trials are small and short.

Checked 2026-11-13

Status: A daily life factor, not a product.
Also called: sleep length, hours of sleep, how long you sleep, short sleep, long sleep, sleep debt, sleep deprivation, sleep restriction, sleep extension, getting more sleep, 8 hours of sleep
Studied for: living longer, heart health, diabetes prevention, blood sugar, weight control, appetite, mood, depression, focus, memory, alertness, immunity, fewer colds, vaccine response, blood pressure

Strong several reviews agree · Moderate one review or consistent trials · Limited one or a few small studies · Untested no study in people, listed with what it rests on

Shown to help9

StrongLinked to the lowest death rates at about 7 hours a night in pooled cohorts, a J or U shape, with a steeper rise for long sleep than for short.
StrongLinked to more heart disease and stroke at both short and long sleep in pooled cohorts, with the lowest risk near 7 hours a night.
StrongLinked to more type 2 diabetes at both short and long sleep in pooled cohorts, a U shape with the lowest risk at 7 to 8 hours a night.
StrongLinked to more new obesity in short sleepers in pooled cohorts. Long sleep was not linked to obesity in one review and weakly linked in another.
ModerateShown to raise food intake by about 385 kcal a day when sleep was cut. One trial of sleep extension in short sleepers found 270 kcal less eaten daily.
ModerateLinked to more new depression at both short and long sleep in one meta-analysis of seven cohorts.
ModerateShown to lower positive mood and raise negative mood when sleep was cut or skipped, in one meta-analysis of 64 experimental studies.
ModerateShown to impair attention after total sleep loss in pooled experiments, and 14 nights of 6 hours or less in bed caused growing deficits in one trial.
LimitedLimited evidence: sleeping under 6 hours was linked to more colds after viral exposure in one study and to weaker vaccine antibody responses when sleep was measured objectively.

Reported risks2

StrongLinked to higher stroke and death rates in people sleeping long hours, in two meta-analyses of cohorts. The rise grew with each extra hour.How often is not known
ModerateShown to lower insulin sensitivity when sleep was restricted, in a meta-analysis of randomized trials, measured by glucose tolerance tests, HOMA-IR and the clamp.How often is not known

What it was studied for, and what was found

Shown to help9

Strong

Death from any cause

Linked to the lowest death rates at about 7 hours a night in pooled cohorts, a J or U shape, with a steeper rise for long sleep than for short.

Compared with people sleeping 7 to 8 hours a night, the reference in most studies [1]; people sleeping 7 hours a day [2]; normal sleepers [3]; people with normal sleep duration [4]

The numbers and sources

Effect: A dose-response meta-analysis found a U-shaped curve with the lowest risk at about 7 hours a day. Below 7 hours, risk rose 6% per hour less (RR 1.06, 95% CI 1.04 to 1.07). Above 7 hours, it rose 13% per hour more (RR 1.13, 95% CI 1.11 to 1.15). The shortest and longest groups had RRs of 1.13 and 1.35 [1]. A spline analysis of 40 cohorts found a J shape: against 7 hours, RR was 1.06 at 5 hours, 1.04 at 6 hours, 1.03 at 8 hours, 1.13 at 9 hours, 1.25 at 10 hours and 1.38 at 11 hours [2]. Short sleepers had a 12% higher risk (RR 1.12, 95% CI 1.08 to 1.16), with a linear rise below 6 hours [3]. Long sleepers had a 39% higher risk (RR 1.39, 95% CI 1.31 to 1.47) [4].
Population: 3,582,016 participants in 67 articles, follow-up 2.3 to 34 years [1]. 2,200,425 participants with 271,507 deaths in 40 cohorts [2]. 5,172,710 participants in 153 studies [3]. 5,134,036 participants in 137 cohorts [4].
Sources: [1], [2], [3], [4]
Caveats: Observational. Sleep was self-reported by questionnaire in most cohorts. Confounding is likely, and reverse causation is a strong candidate for long sleep: illness, depression and low fitness lengthen sleep, and some illnesses shorten it. The authors of the long sleep review call for work on whether the link is causal [4]. Heterogeneity was high for long sleep (I² 76.2%) [1]. In one review, short sleep was linked to higher risk in women and not in men [2].

Strong

Heart disease and stroke

Linked to more heart disease and stroke at both short and long sleep in pooled cohorts, with the lowest risk near 7 hours a night.

Compared with people sleeping 7 to 8 hours a night, the reference in most studies [1]; normal sleepers [3]; people with normal sleep duration [4]

The numbers and sources

Effect: Each hour under 7 was linked to 6% more total cardiovascular disease (RR 1.06, 95% CI 1.03 to 1.08) and 7% more coronary heart disease (RR 1.07, 95% CI 1.03 to 1.12). Each hour over 7 was linked to 12% more cardiovascular disease (RR 1.12) and 18% more stroke (RR 1.18, 95% CI 1.14 to 1.21) [1]. Short sleepers had higher risk of cardiovascular disease (RR 1.16, 95% CI 1.10 to 1.23), coronary heart disease (RR 1.26) and hypertension (RR 1.17) [3]. Long sleepers had higher risk of cardiovascular disease (RR 1.25), stroke (RR 1.46, 95% CI 1.26 to 1.69) and coronary heart disease (RR 1.24), and no higher risk of hypertension (RR 1.01, 95% CI 0.95 to 1.07) [4].
Population: 3,582,016 participants in generally healthy populations, follow-up 2.3 to 34 years [1]. 5,172,710 participants in 153 studies [3]. 5,134,036 participants in 137 cohorts [4].
Sources: [1], [3], [4]
Caveats: Observational, with self-reported sleep. Confounding and reverse causation, where early heart disease or other illness changes sleep, cannot be ruled out. The three reviews draw on overlapping cohorts.

Strong

Type 2 diabetes

Linked to more type 2 diabetes at both short and long sleep in pooled cohorts, a U shape with the lowest risk at 7 to 8 hours a night.

Compared with people sleeping 7 hours a day [5]; normal sleepers [3]; people with normal sleep duration [4]

The numbers and sources

Effect: Against 7 hours, each hour shorter among people sleeping under 7 hours was linked to 9% more type 2 diabetes (RR 1.09, 95% CI 1.04 to 1.15), and each hour longer among long sleepers to 14% more (RR 1.14, 95% CI 1.03 to 1.26) [5]. Short sleepers had a 37% higher risk (RR 1.37, 95% CI 1.22 to 1.53) [3]. Long sleepers had a 26% higher risk (RR 1.26, 95% CI 1.11 to 1.43) [4].
Population: 482,502 participants with 18,443 cases, follow-up 2.5 to 16 years [5]. 5,172,710 participants in 153 studies [3]. 5,134,036 participants in 137 cohorts [4].
Sources: [5], [3], [4]
Caveats: Observational. Confounding by weight, activity and mood is likely, and reverse causation is possible because early metabolic disease and its symptoms can disturb sleep.

Strong

Weight and obesity

Linked to more new obesity in short sleepers in pooled cohorts. Long sleep was not linked to obesity in one review and weakly linked in another.

Compared with people with normal sleep duration [6]; normal sleepers [3]; people with normal sleep duration [4]

The numbers and sources

Effect: Short sleep was linked to higher odds of later obesity (OR 1.45, 95% CI 1.25 to 1.67), and 1.25 (95% CI 1.14 to 1.38) after removing three studies that drove the heterogeneity. Long sleep was not (OR 1.06, 95% CI 0.98 to 1.15) [6]. Another review found a 38% higher risk of obesity in short sleepers (RR 1.38, 95% CI 1.25 to 1.53) [3], and a third an 8% higher risk in long sleepers (RR 1.08, 95% CI 1.02 to 1.15) [4].
Population: 197,906 participants for short sleep and 164,016 for long sleep in 11 prospective studies [6]. 5,172,710 participants in 153 studies [3]. 5,134,036 participants in 137 cohorts [4].
Sources: [6], [3], [4]
Caveats: Observational. Diet, activity, screen use and mood can affect both sleep and weight, and weight gain itself can disturb sleep. The European subgroup showed no clear link (OR 1.45, 95% CI 0.79 to 2.64) [6].

Moderate

Eating and weight in sleep loss and sleep extension trials

Shown to raise food intake by about 385 kcal a day when sleep was cut. One trial of sleep extension in short sleepers found 270 kcal less eaten daily.

Compared with a control condition with usual sleep [7]; people who kept their habitual sleep [8]

The numbers and sources

Effect: Partial sleep deprivation raised energy intake by 385 kcal a day (95% CI 252 to 517) with no change in total energy expenditure or resting metabolic rate. Fat intake rose and protein intake fell [7]. In adults with overweight who slept under 6.5 hours, sleep hygiene counseling lengthened sleep by about 1.2 hours a night and cut energy intake by 270 kcal a day (95% CI -393 to -147) against controls over 2 weeks. Weight changed by -0.87 kg (95% CI -1.39 to -0.35) relative to controls [8].
Population: 496 participants in 17 studies, 172 in the 11 pooled [7]. 80 adults aged 21 to 40 with a BMI of 25.0 to 29.9 [8].
Sources: [7], [8]
Caveats: The restriction studies lasted days and many were done in a laboratory [7]. The extension result comes from one 2-week trial. Whether the change in intake lasts was not measured [8].

Moderate

Depression

Linked to more new depression at both short and long sleep in one meta-analysis of seven cohorts.

Compared with people with normal sleep duration [9]

The numbers and sources

Effect: Short sleep was linked to a 31% higher risk of depression (RR 1.31, 95% CI 1.04 to 1.64) and long sleep to a 42% higher risk (RR 1.42, 95% CI 1.04 to 1.92), with no heterogeneity (I² 0%) [9]. A larger review found too little usable data to pool depression [3].
Population: 25,271 participants for short sleep and 23,663 for long sleep in 7 prospective studies [9].
Sources: [9], [3]
Caveats: Observational and few studies. Disturbed sleep is itself a symptom of depression, so early illness may change sleep before diagnosis, which is reverse causation.

Moderate

Mood after sleep loss

Shown to lower positive mood and raise negative mood when sleep was cut or skipped, in one meta-analysis of 64 experimental studies.

Compared with control conditions the source does not describe [10]

The numbers and sources

Effect: Sleep loss had a large negative effect on positive mood (g -0.94) and a moderate effect raising negative mood (g 0.45). Total sleep deprivation raised negative mood more than partial restriction. Sleep restriction had a small negative effect on adaptive emotion regulation (g -0.32) [10].
Population: 241 effect sizes from 64 studies, from early childhood to late adulthood [10].
Sources: [10]
Caveats: Short experimental studies of acute loss. They do not show what years of habitual short sleep do to mood. The emotion regulation studies were all in young people [10].

Moderate

Attention and thinking

Shown to impair attention after total sleep loss in pooled experiments, and 14 nights of 6 hours or less in bed caused growing deficits in one trial.

Compared with a baseline test in the same people, or a control group [11]; 8 hours in bed a night [12]

The numbers and sources

Effect: Short-term total sleep deprivation had its largest effect on lapses in simple attention (g -0.776, 95% CI -0.96 to -0.60) and a small, nonsignificant effect on reasoning accuracy (g -0.125, 95% CI -0.27 to 0.02) [11]. Restricting time in bed to 4 or 6 hours for 14 days caused cumulative, dose-dependent deficits on all tasks, equal to up to 2 nights without sleep. Sleepiness ratings rose little after the first days, so people largely did not notice their growing deficits [12].
Population: 147 cognitive tests in 70 articles of under 48 hours of total sleep deprivation [11]. 48 healthy adults aged 21 to 38 in a laboratory [12].
Sources: [11], [12]
Caveats: Laboratory studies in healthy young adults. Total deprivation is more extreme than everyday short sleep. The restriction trial was small [12].

Limited

Colds and vaccine response

Limited evidence: sleeping under 6 hours was linked to more colds after viral exposure in one study and to weaker vaccine antibody responses when sleep was measured objectively.

Compared with people sleeping more than 7 hours a night [16]; people not sleeping under 6 hours a night [17]

The numbers and sources

Effect: After rhinovirus nasal drops, adults whose wrist-measured sleep was under 5 hours had higher odds of a clinical cold (OR 4.50, 95% CI 1.08 to 18.69), as did those sleeping 5 to 6 hours (OR 4.24). Those sleeping 6.01 to 7 hours did not (OR 1.66, 95% CI 0.40 to 6.95) [16]. Objectively measured short sleep was linked to a lower antibody response to vaccination (effect size 0.79, 95% CI 0.40 to 1.18). Self-reported short sleep was not (0.29, 95% CI -0.04 to 0.63). The link was significant in men and not in women [17].
Population: 164 healthy adults aged 18 to 55, quarantined [16]. 304 adults with objective sleep measures and 504 with self-reported sleep [17].
Sources: [16], [17]
Caveats: Sleep was observed, not assigned, so other differences between short and long sleepers may explain the results. Intervals were wide [16]. Antibody levels are not infections prevented.

Mixed results1

Moderate

Sleep extension and blood pressure, glucose and insulin

Mixed results: pooled sleep extension trials found no overall change in blood pressure, fasting glucose or insulin resistance. Blood pressure fell in people with raised pressure.

Compared with control or baseline conditions the source does not describe [14]; control or baseline conditions the source does not describe [15]

The numbers and sources

Effect: Sleep extension lengthened total sleep by 51 minutes (95% CI 39 to 63) and did not change blood pressure overall. In people with pre-hypertension or stage 1 hypertension, 24-hour systolic pressure fell 7.8 mmHg (95% CI -10.6 to -4.9) and diastolic pressure 4.2 mmHg. Pooled effects on fasting glucose and insulin resistance were not significant [14]. A systematic review of 7 extension studies reported better direct and indirect measures of insulin sensitivity, less appetite and less desire for sweet and salty foods [15].
Population: 13 studies from 11 trials, 3 days to 6 weeks, adults without a sleep disorder [14]. 138 participants in 7 studies, mostly short sleepers [15].
Sources: [14], [15]
Caveats: Small and short trials. The blood pressure fall is a subgroup result. The review of 7 studies gave no pooled estimates [15].

Amounts studied

Cohort studies measured sleep mostly by questionnaire. Most used 7 to 8 hours a night as the reference group [1], and the dose-response reviews placed the lowest risk at about 7 hours [1][2] or 7 to 8 hours [5]. Short sleep was usually under 6 or 7 hours and long sleep 9 hours or more, as each cohort defined it.

Experiments used total sleep deprivation for under 48 hours [11], 4, 6 or 8 hours in bed for 14 nights [12], and partial deprivation over days [7]. Extension trials ran from 3 days to 6 weeks and added 21 to 177 minutes of sleep [14][15]. The largest extension trial aimed for 8.5 hours in bed and added about 1.2 hours a night for 2 weeks [8]. The cold study measured a week of sleep by wrist actigraph before viral exposure [16].

Risks

Reported risks2

ModerateHow often is not known

Lower insulin sensitivity with short sleep

Shown to lower insulin sensitivity when sleep was restricted, in a meta-analysis of randomized trials, measured by glucose tolerance tests, HOMA-IR and the clamp.

The numbers and sources

How common: How often is not known: the sources give no rate.
Effect: Across 21 pooled sleep restriction studies, insulin sensitivity fell when measured by oral or intravenous glucose tolerance tests and by the homeostatic model assessment of insulin resistance (HOMA-IR). Whole-body insulin sensitivity measured by the hyperinsulinemic euglycemic clamp also fell. Peripheral insulin sensitivity did not change [13].
Population: 35 randomized controlled trials, 26 of sleep restriction and 21 of these pooled [13].
Sources: [13]
Caveats: Short laboratory trials. The abstract gives no pooled effect sizes. A fall in insulin sensitivity over days does not show that habitual short sleep causes diabetes.

StrongHow often is not known

Long sleep linked to stroke and death

Linked to higher stroke and death rates in people sleeping long hours, in two meta-analyses of cohorts. The rise grew with each extra hour.

The numbers and sources

How common: How often is not known: the sources give no rate.
Effect: Long sleepers had a 46% higher stroke risk (RR 1.46, 95% CI 1.26 to 1.69) and a 39% higher death rate (RR 1.39, 95% CI 1.31 to 1.47) than people with normal sleep duration, with a linear rise as sleep lengthened [4]. Each hour over 7 was linked to 18% more stroke (RR 1.18) and 13% more deaths (RR 1.13) against people sleeping 7 to 8 hours [1].
Population: 5,134,036 participants in 137 cohorts [4]. 3,582,016 participants in 67 articles [1].
Sources: [4], [1]
Caveats: Observational. Long sleep often follows illness, depression or low activity, so reverse causation may explain much of the link. No trial has tested shortening sleep in long sleepers.

Claims tested and not found

That people adapt to sleeping 6 hours or less. Over 14 nights at 4 or 6 hours in bed, attention deficits kept growing while sleepiness ratings barely changed [12].
That long sleep is linked to obesity. In 11 prospective studies, long sleep was not linked to later obesity (OR 1.06, 95% CI 0.98 to 1.15) [6].
That long sleep is linked to high blood pressure. In 137 cohorts, long sleep was not linked to new hypertension (RR 1.01, 95% CI 0.95 to 1.07) [4].
That sleeping longer lowers blood pressure in everyone. Pooled extension trials found no change in blood pressure overall, only in people with raised pressure [14].

Sleep trackers Melatonin

Sources

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. https://doi.org/10.1161/JAHA.117.005947
Liu TZ, Xu C, Rota M, et al. Sleep duration and risk of all-cause mortality: A flexible, non-linear, meta-regression of 40 prospective cohort studies. Sleep Medicine Reviews. 2017. https://doi.org/10.1016/j.smrv.2016.02.005
Itani O, Jike M, Watanabe N, Kaneita Y. Short sleep duration and health outcomes: a systematic review, meta-analysis, and meta-regression. Sleep Medicine. 2017. https://doi.org/10.1016/j.sleep.2016.08.006
Jike M, Itani O, Watanabe N, et al. Long sleep duration and health outcomes: A systematic review, meta-analysis and meta-regression. Sleep Medicine Reviews. 2018. https://doi.org/10.1016/j.smrv.2017.06.011
Shan Z, Ma H, Xie M, et al. Sleep duration and risk of type 2 diabetes: a meta-analysis of prospective studies. Diabetes Care. 2015. https://doi.org/10.2337/dc14-2073
Wu Y, Zhai L, Zhang D. Sleep duration and obesity among adults: a meta-analysis of prospective studies. Sleep Medicine. 2014. https://doi.org/10.1016/j.sleep.2014.07.018
Al Khatib HK, Harding SV, Darzi J, Pot GK. The effects of partial sleep deprivation on energy balance: a systematic review and meta-analysis. European Journal of Clinical Nutrition. 2017. https://doi.org/10.1038/ejcn.2016.201
Tasali E, Wroblewski K, Kahn E, et al. 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. https://doi.org/10.1001/jamainternmed.2021.8098
Zhai L, Zhang H, Zhang D. Sleep duration and depression among adults: a meta-analysis of prospective studies. Depression and Anxiety. 2015. https://doi.org/10.1002/da.22386
Tomaso CC, Johnson AB, Nelson TD. The effect of sleep deprivation and restriction on mood, emotion, and emotion regulation: three meta-analyses in one. Sleep. 2021. https://doi.org/10.1093/sleep/zsaa289
Lim J, Dinges DF. A meta-analysis of the impact of short-term sleep deprivation on cognitive variables. Psychological Bulletin. 2010. https://doi.org/10.1037/a0018883
Van Dongen HP, Maislin G, Mullington JM, Dinges DF. The cumulative cost of additional wakefulness: dose-response effects on neurobehavioral functions and sleep physiology from chronic sleep restriction and total sleep deprivation. Sleep. 2003. https://doi.org/10.1093/sleep/26.2.117
Sondrup N, Termannsen AD, Eriksen JN, et al. Effects of sleep manipulation on markers of insulin sensitivity: A systematic review and meta-analysis of randomized controlled trials. Sleep Medicine Reviews. 2022. https://doi.org/10.1016/j.smrv.2022.101594
Zhu B, Yin Y, Shi C, et al. Feasibility of sleep extension and its effect on cardiometabolic parameters in free-living settings: a systematic review and meta-analysis of experimental studies. European Journal of Cardiovascular Nursing. 2022. https://doi.org/10.1093/eurjcn/zvab055
Henst RHP, Pienaar PR, Roden LC, Rae DE. The effects of sleep extension on cardiometabolic risk factors: A systematic review. Journal of Sleep Research. 2019. https://doi.org/10.1111/jsr.12865
Prather AA, Janicki-Deverts D, Hall MH, Cohen S. Behaviorally Assessed Sleep and Susceptibility to the Common Cold. Sleep. 2015. https://doi.org/10.5665/sleep.4968
Spiegel K, Rey AE, Cheylus A, et al. A meta-analysis of the associations between insufficient sleep duration and antibody response to vaccination. Current Biology. 2023. https://doi.org/10.1016/j.cub.2023.02.017

Everything in the library

Shown to help9

Reported risks2

What it was studied for, and what was found

Shown to help9

Mixed results1

Amounts studied

Risks

Reported risks2

Claims tested and not found

Related

Sources