Sleep duration and regularity
hours / night
How long people sleep and how regular that schedule is. Restriction trials show hormones and insulin can move within a few short nights.
Partial sleep restriction raises evening cortisol, lowers next-day testosterone in men, and worsens insulin sensitivity within nights. Wearable trackers measure the same clock; they do not create the effect. Hours in bed are not the same as night-shift timing or an apnea count.
Also called sleep restriction, circadian.
Connected relationships
Meta-analysis · High confidence
Sleep duration and regularity→Cognitive performance
Higher Sleep duration and regularity increases Cognitive performance.
Lim and Dinges's 2010 meta of short-term deprivation shows losses on vigilance and working memory. Santisteban's 2019 adult week and Lo's 2016 adolescent week then lose working memory; Lo also loses vigilance. Zimmerman's 2024 habit trial moves the same tasks.
Randomized trial · High confidence
Sleep duration and regularity→Cortisol
Higher Sleep duration and regularity decreases Cortisol.
Six 4-hour nights raised evening cortisol in eleven young men. Four nights of 5-to-9-hour beds in eighty-eight adolescents did not move evening or morning saliva cortisol.
Randomized trial · Moderate
Sleep duration and regularity→Depression
A rise in Sleep duration and regularity does not identify a change in Depression.
In 126 adults with insomnia and major depression, adding internet CBT for insomnia to CBT for depression improved the insomnia score but not the depression score versus depression treatment plus a placebo sleep module.
Randomized trial · High confidence
Sleep duration and regularity→Insulin resistance (HOMA-IR)
Higher Sleep duration and regularity decreases Insulin resistance (HOMA-IR).
Experimental sleep restriction lowers insulin sensitivity. Spiegel, Leproult, and Van Cauter put eleven young men into sleep debt and watched glucose tolerance fall into a pre-diabetic range. Later randomized weeks, including clamp studies and a six-week trial in thirty-eight women, found the same direction.
Meta-analysis · Low
Sleep duration and regularity→All-cause mortality
Higher Sleep duration and regularity moves All-cause mortality in a non-linear way. Dose or timing can flip the sign.
Yin 2018's dose-response meta of prospective cohorts found a U-shaped link between hours of sleep and all-cause death: each hour under 7 tracked a 6 percent higher risk, and each hour over 7 tracked 13 percent. Nobody randomized time in bed.
Randomized trial · Moderate
Sleep duration and regularity→Testosterone
Higher Sleep duration and regularity increases Testosterone.
In men, experimental sleep loss lowers testosterone. A week of 5-hour nights cut daytime T about 10 to 15 percent. One night of total wake cut 24-hour T. All-night deprivation cut total T; REM-only did not. In 37 healthy adults, T also fell during long wake; caffeine lessened that drop.
Review · High confidence
Alcohol intake→Sleep duration and regularity
Higher Alcohol intake decreases Sleep duration and regularity.
Evening alcohol, 1.0 grams per kilogram in men and 0.85 in women, cut total sleep time from 436.6 to 421.3 minutes and sleep efficiency from 91.2 to 88.0 percent in thirty-one social drinkers on a randomized crossover with overnight PSG.
Randomized trial · Contested
Ashwagandha→Sleep duration and regularity
Higher Ashwagandha increases Sleep duration and regularity.
Deshpande 2021 found that 120 mg a day of a standardized ashwagandha extract for six weeks raised self-reported restorative sleep by 72 percent versus 29 percent on placebo among 150 adults with non-restorative sleep, and actigraphy moved efficiency, total sleep, latency, and wake after sleep onset. Langade 2021 found a similar direction in 80 people, stronger in the insomnia arm.
Randomized trial · Moderate
Caffeine intake→Sleep duration and regularity
Higher Caffeine intake moves Sleep duration and regularity only in some conditions. Read the mechanism.
In twenty young men, Weibel 2021 found that 450 mg of daytime caffeine a day left nighttime sleep length and stages unchanged, but delayed REM and made waking harder when sleep was pushed into the morning.
Randomized trial · Contested
Chamomile→Sleep duration and regularity
Higher Chamomile increases Sleep duration and regularity.
Chang 2016 found that two weeks of chamomile tea lowered a physical-symptoms sleep-inefficiency score versus usual care in 80 Taiwanese postnatal women with poor sleep (P=0.015). The difference was gone two weeks after the tea stopped. There was no placebo drink.
Randomized trial · Moderate
Evening and bright light→Sleep duration and regularity
Higher Evening and bright light decreases Sleep duration and regularity.
Chang 2015 randomized twelve young adults: five evenings of a light-emitting e-reader versus a printed book delayed dim-light melatonin onset by more than 1.5 hours, suppressed evening melatonin by about 55 percent, and lengthened sleep latency by about ten minutes.
Randomized trial · Contested
Magnesium supplementation→Sleep duration and regularity
Higher Magnesium supplementation increases Sleep duration and regularity.
Schuster 2025 found that 250 mg of magnesium bisglycinate a day for four weeks lowered the Insomnia Severity Index by 3.9 points versus 2.3 on placebo in 155 adults who reported poor sleep (P=0.049). Hausenblas 2024 saw better deep and REM scores on magnesium L-threonate versus placebo in 80 people.
Randomized trial · Contested
Melatonin supplementation→Sleep duration and regularity
Higher Melatonin supplementation moves Sleep duration and regularity only in some conditions. Read the mechanism.
Luthringer 2009 found that 2 mg of prolonged-release melatonin at night shortened polysomnographic sleep-onset latency by 9 minutes versus placebo in 40 people aged 55 or older with primary insomnia (P=0.02). Baandrup 2017 found no change in sleep efficiency when the same kind of tablet was added during benzodiazepine withdrawal in schizophrenia or bipolar disorder.
Meta-analysis · Low
Nighttime transportation noise→Sleep duration and regularity
Higher Nighttime transportation noise decreases Sleep duration and regularity.
In a 2022 update of the WHO sleep review, each extra 10 dB of night-time road, rail, or aircraft noise raised the odds of being highly sleep disturbed about two- to three-fold when the question named the noise, across 36 observational studies and 173,160 responses. Nobody randomized the street.
Randomized trial · Contested
Tart cherry→Sleep duration and regularity
Higher Tart cherry moves Sleep duration and regularity only in some conditions. Read the mechanism.
Losso 2018 found that 240 mL of Montmorency tart cherry juice twice a day for two weeks added 84 minutes of laboratory sleep time versus placebo in eight adults over 50 with insomnia. Howatson 2013 saw a similar direction in twenty healthy adults; Hillman found no sleep difference in forty-four healthy adults over thirty days.
Randomized trial · Contested
Valerian→Sleep duration and regularity
Higher Valerian increases Sleep duration and regularity.
Taavoni 2011 found that 530 mg of valerian extract twice a day for four weeks raised the share of postmenopausal women whose Pittsburgh Sleep Quality Index improved to 30 percent versus 4 percent on placebo (n=100). Chandra Shekhar 2024 found a similar PSQI and actigraphy direction in 72 completers. Donath 2000's sixteen-person polysomnography was thinner.
Cases
Sources
- J. Lim et al. (2010). A meta-analysis of the impact of short-term sleep deprivation on cognitive variables
- ME Zimmerman et al. (2024). The effects of insufficient sleep and adequate sleep on cognitive function in healthy adults.
- JA Santisteban et al. (2019). Cumulative mild partial sleep deprivation negatively impacts working memory capacity but not sustained attention, response inhibition, or decision making: a randomized controlled trial.
- JC Lo et al. (2016). Cognitive Performance, Sleepiness, and Mood in Partially Sleep Deprived Adolescents: The Need for Sleep Study.
- K. Spiegel et al. (1999). Impact of sleep debt on metabolic and endocrine function
- U Voderholzer et al. (2012). The impact of increasing sleep restriction on cortisol and daytime sleepiness in adolescents.
- K Blom et al. (2024). Psychological Treatment of Comorbid Insomnia and Depression: A Double-Blind Randomized Placebo-Controlled Trial.
- CE Carney et al. (2017). Cognitive Behavioral Insomnia Therapy for Those With Insomnia and Depression: A Randomized Controlled Clinical Trial.
- AV Nedeltcheva et al. (2009). Exposure to recurrent sleep restriction in the setting of high caloric intake and physical inactivity results in increased insulin resistance and reduced glucose tolerance.
- OM Buxton et al. (2010). Sleep restriction for 1 week reduces insulin sensitivity in healthy men.
- AV Nedeltcheva et al. (2012). Effects of sleep restriction on glucose control and insulin secretion during diet-induced weight loss.
- JL Broussard et al. (2013). Impaired insulin signaling in human adipocytes after experimental sleep restriction: a randomized, crossover study.
- MN Rao et al. (2015). Subchronic sleep restriction causes tissue-specific insulin resistance.
- J Cros et al. (2019). Impact of sleep restriction on metabolic outcomes induced by overfeeding: a randomized controlled trial in healthy individuals.
- P Singh et al. (2023). Effect of sleep restriction on insulin sensitivity and energy metabolism in postmenopausal women: A randomized crossover trial.
- FM Zuraikat et al. (2023). Chronic Insufficient Sleep in Women Impairs Insulin Sensitivity Independent of Adiposity Changes: Results of a Randomized Trial.
- OM Buxton et al. (2012). Adverse metabolic consequences in humans of prolonged sleep restriction combined with circadian disruption.
- KM Ness et al. (2020). Two nights of recovery sleep restores the dynamic lipemic response, but not the reduction of insulin sensitivity, induced by five nights of sleep restriction.
- J Yin et al. (2018). Relationship of Sleep Duration With All-Cause Mortality and Cardiovascular Events: A Systematic Review and Dose-Response Meta-Analysis of Prospective Cohort Studies.
- TZ Liu et al. (2018). Sleep duration and risk of all-cause mortality: A flexible, non-linear, meta-regression of 40 prospective cohort studies.
- FP Cappuccio et al. (2010). Sleep duration and all-cause mortality: a systematic review and meta-analysis of prospective studies.
- DP Windred et al. (2024). Sleep regularity is a stronger predictor of mortality risk than sleep duration: A prospective cohort study.
- YY Liang et al. (2023). Joint Associations of Device-Measured Sleep Duration and Efficiency With All-Cause and Cause-Specific Mortality: A Prospective Cohort Study of 90 398 UK Biobank Participants.
- D Liu et al. (2023). Association of 3-year change in sleep duration with risk of all-cause mortality in Chinese older population: A national cohort study.
- YY Liang et al. (2023). Joint association of physical activity and sleep duration with risk of all-cause and cause-specific mortality: a population-based cohort study using accelerometry.
- R. Leproult et al. (2011). Effect of 1 week of sleep restriction on testosterone levels in young healthy men
- PY Liu et al. (2021). Age and time-of-day differences in the hypothalamo-pituitary-testicular, and adrenal, response to total overnight sleep deprivation.
- B Faraut et al. (2020). Daytime Exposure to Blue-Enriched Light Counters the Effects of Sleep Restriction on Cortisol, Testosterone, Alpha-Amylase and Executive Processes.
- TA Alvarenga et al. (2023). The effects of sleep deprivation and obstructive sleep apnea syndrome on male reproductive function: a multi-arm randomised trial.
- C Drogou et al. (2023). Effects of Acute Caffeine Intake on Insulin-Like Growth Factor-1 Responses to Total Sleep Deprivation: Interactions with COMT Polymorphism - A Randomized, Crossover Study.
- M. A. Emanuele et al. (2001). Alcohol and the male reproductive system
- E Pabon et al. (2022). Effects of alcohol on sleep and nocturnal heart rate: Relationships to intoxication and morning-after effects.
- A Deshpande et al. (2021). A randomized, double blind, placebo controlled study to evaluate the effects of ashwagandha (Withania somnifera) extract on sleep quality in healthy adults.
- D Langade et al. (2021). Clinical evaluation of the pharmacological impact of ashwagandha root extract on sleep in healthy volunteers and insomnia patients: A double-blind, randomized, parallel-group, placebo-controlled study.
- J Weibel et al. (2021). The impact of daily caffeine intake on nighttime sleep in young adult men.
- J Weibel et al. (2021). Regular Caffeine Intake Delays REM Sleep Promotion and Attenuates Sleep Quality in Healthy Men.
- SM Chang et al. (2016). Effects of an intervention with drinking chamomile tea on sleep quality and depression in sleep disturbed postnatal women: a randomized controlled trial.
- AM Chang et al. (2015). Evening use of light-emitting eReaders negatively affects sleep, circadian timing, and next-morning alertness.
- G Zerbini et al. (2021). Strategies to decrease social jetlag: Reducing evening blue light advances sleep and melatonin.
- SL Chellappa et al. (2014). Acute exposure to evening blue-enriched light impacts on human sleep.
- N Santhi et al. (2012). The spectral composition of evening light and individual differences in the suppression of melatonin and delay of sleep in humans.
- A Green et al. (2018). Evening light exposure to computer screens disrupts human sleep, biological rhythms, and attention abilities.
- LE Hartstein et al. (2022). High sensitivity of melatonin suppression response to evening light in preschool-aged children.
- MC Gordijn et al. (1999). Effects of light exposure and sleep displacement on dim light melatonin onset.
- L Tähkämö et al. (2020). Systematic review of light exposure impact on human circadian rhythm.
- J Schuster et al. (2025). Magnesium Bisglycinate Supplementation in Healthy Adults Reporting Poor Sleep: A Randomized, Placebo-Controlled Trial.
- HA Hausenblas et al. (2025). Magnesium-L-threonate improves sleep quality and daytime functioning in adults with self-reported sleep problems: A randomized controlled trial.
- R Luthringer et al. (2009). The effect of prolonged-release melatonin on sleep measures and psychomotor performance in elderly patients with insomnia.
- L Baandrup et al. (2017). Objective and subjective sleep quality: Melatonin versus placebo add-on treatment in patients with schizophrenia or bipolar disorder withdrawing from long-term benzodiazepine use.
- MG Smith et al. (2022). Environmental Noise and Effects on Sleep: An Update to the WHO Systematic Review and Meta-Analysis.
- M Schubert et al. (2023). Traffic-Related High Sleep Disturbance in the LIFE-Adult Cohort Study: A Comparison to the WHO Exposure-Response-Curves.
- S Perron et al. (2017). Sleep Disturbance from Road Traffic, Railways, Airplanes and from Total Environmental Noise Levels in Montreal.
- S Perron et al. (2012). Review of the effect of aircraft noise on sleep disturbance in adults.
- S Pirrera et al. (2010). Nocturnal road traffic noise: A review on its assessment and consequences on sleep and health.
- JN Losso et al. (2018). Pilot Study of the Tart Cherry Juice for the Treatment of Insomnia and Investigation of Mechanisms.
- G Howatson et al. (2013). Effect of tart cherry juice (Prunus cerasus) on melatonin levels and enhanced sleep quality.
- WR Pigeon et al. (2010). Effects of a tart cherry juice beverage on the sleep of older adults with insomnia: a pilot study.
- AR Hillman et al. (2026). Montmorency tart cherry supplementation does not impact sleep, body composition, cellular health, or blood pressure in healthy adults.
- S Taavoni et al. (2011). Effect of valerian on sleep quality in postmenopausal women: a randomized placebo-controlled clinical trial.
- H Chandra Shekhar et al. (2024). Standardized Extract of Valeriana officinalis Improves Overall Sleep Quality in Human Subjects with Sleep Complaints: A Randomized, Double-Blind, Placebo-Controlled, Clinical Study.
- F Donath et al. (2000). Critical evaluation of the effect of valerian extract on sleep structure and sleep quality.