Sleep timing
Pooled observational studies link an evening chronotype and social jet lag of 2 hours or more to more depression, and social jet lag to higher body weight. Irregular sleep is linked to cardiometabolic risk, with mixed results for death. Later school start times added about an hour of sleep in teenagers. One trial shifting night owls earlier eased depression.
Checked 2026-11-13
- Status
- A daily life factor, not a product.
- Also called
- chronotype, night owl, early bird, morning person, evening person, eveningness, morningness, late bedtime, bedtime, sleep schedule, irregular sleep, sleep regularity, consistent sleep schedule, social jet lag, social jetlag, weekend sleep-in, catch-up sleep, school start times
- Studied for
- mood, depression, weight control, blood sugar, diabetes prevention, heart health, living longer, focus, energy, teen sleep, being a morning person
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 help2
- StrongShown to lengthen teenagers' sleep by about 25 to 77 minutes a night when school started later, in three reviews. Depressive symptoms fell slightly in pooled studies.
- LimitedOne trial moved night owls' sleep and wake times about 2 hours earlier and found less depression and stress and better morning reaction time and grip strength.
Reported risks9
- StrongLinked to more depression in evening types in three meta-analyses, mostly cross-sectional, with about 80% higher odds and a small correlation with symptom severity.How often is not known
- StrongLinked to more depressive symptoms with social jet lag in three meta-analyses, a weak correlation, with higher odds at 2 hours or more than at 1 to 2 hours.How often is not known
- ModerateLinked to higher body mass index, body fat and waist size with more social jet lag in two meta-analyses, small correlations with very high heterogeneity.How often is not known
- ModerateLinked to 30% higher odds of diabetes in evening types in one meta-analysis and one large cohort, with higher blood glucose and HbA1c in cross-sectional data.How often is not known
- ModerateMixed results: one meta-analysis linked evening chronotype to 18% higher odds of cancer, and a systematic review of 22 studies found no consistent link for late timing.How often is not known
- ModerateMixed results: the least regular sleepers had 20% to 88% higher death rates in several cohorts, but a meta-analysis found day-to-day rhythm stability not linked to death.How often is not known
- ModerateLinked to higher body mass index, insulin resistance, high blood pressure and heart events with irregular sleep timing in two systematic reviews that did not pool results.How often is not known
- LimitedOne large cohort linked falling asleep before 10 p.m., between 11 and midnight, or after midnight to 12% to 25% more cardiovascular disease than 10 to 11 p.m.How often is not known
- LimitedOne large cohort linked being a definite evening type to 10% higher death from any cause than being a definite morning type.How often is not known
What it was studied for, and what was found
Shown to help2
Shifting night owls to an earlier schedule
One trial moved night owls' sleep and wake times about 2 hours earlier and found less depression and stress and better morning reaction time and grip strength.
Compared with a control group the abstract does not describe [1]
The numbers and sources
- Effect
- Earlier wake and sleep times, fixed meal times, limits on caffeine and timed exercise advanced sleep and wake timing by about 2 hours, measured by actigraphy, dim light melatonin onset and the cortisol awakening response, with no loss of sleep duration. Self-reported depression and stress improved, and reaction time and grip strength improved in the morning hours [1].
- Population
- Night owls with a late sleep and wake pattern, in one randomized controlled trial in a real-world setting. The abstract does not give the head count or length [1].
- Sources
- [1]
- Caveats
- One small trial. Participants knew their group, and mood and stress were self-rated. The trial changed several habits at once, so it cannot say which mattered.
Later school start times in teenagers
Shown to lengthen teenagers' sleep by about 25 to 77 minutes a night when school started later, in three reviews. Depressive symptoms fell slightly in pooled studies.
Compared with earlier school start times, as each study compared them [2]; the same students before the delay, and control schools in trials [3]; earlier school start times [4]
The numbers and sources
- Effect
- Six studies found later start times linked to more sleep. One study found fewer depressive symptoms, and results for alertness and absences were mixed. The evidence was rated very low in quality [2]. Start times delayed by 25 to 60 minutes were followed by 25 to 77 more minutes of sleep per weeknight, with some studies reporting less daytime sleepiness, depression and caffeine use [3]. Pooled, delayed start times added an average 69 minutes of sleep (SMD 0.63) and lowered depressive symptoms slightly (SMD -0.20) [4].
- Population
- 297,994 students aged 13 to 19 in 11 studies [2]. 6 studies, 2 of them randomized [3]. Middle and high school students in 6 studies [4].
- Sources
- [2], [3], [4]
- Caveats
- Most studies were not randomized and were at high or unclear risk of bias [2]. Heterogeneity was high [4]. Whether the extra sleep lasts was not shown. One study reported less parent and child time [2].
Amounts studied
Chronotype was measured mostly by questionnaire, the Morningness-Eveningness Questionnaire or the Composite Scale of Morningness, scored along a morning to evening scale [5] or grouped as morning and evening types [6]. Social jet lag is the weekly gap in sleep timing between work or school days and free days, measured as a continuous score [7] or in bands of 1 to 2 hours and 2 hours or more [8][9]. Sleep regularity was measured from a week of wrist accelerometer data as the Sleep Regularity Index, with a median of 81 [10], or as interdaily stability of the rest and activity rhythm [11]. Bedtime was measured as accelerometer sleep onset in hourly bands from before 10 p.m. to after midnight [12].
Trials moved night owls' timing about 2 hours earlier with earlier sleep and wake times, set meal times, caffeine limits and exercise [1]. School start times were delayed by 25 to 60 minutes [3].
Risks
Reported risks7
Evening chronotype linked to depression
Linked to more depression in evening types in three meta-analyses, mostly cross-sectional, with about 80% higher odds and a small correlation with symptom severity.
The numbers and sources
- How common
- How often is not known: the sources give no rate.
- Effect
- Eveningness was linked to more severe depressive symptoms, a small effect (Fisher's z -0.20, 95% CI -0.18 to -0.23) [5]. Evening types had higher odds of depression than morning types (OR 1.86, 95% CI 1.20 to 2.88) [6]. Evening chronotype was linked to depression in cross-sectional studies (RR 1.83, 95% CI 1.40 to 2.38), and not significantly in cohorts (RR 1.79, 95% CI 0.59 to 5.46). Morning preference was linked to lower risk in cohorts (RR 0.88, 95% CI 0.81 to 0.96) [13].
- Population
- 15,734 people in 36 studies [5]. 377,797 participants in 39 studies, 37 cross-sectional [6]. 22 studies, 20 cross-sectional and 2 cohorts [13].
- Sources
- [5], [6], [13]
- Caveats
- Observational and mostly cross-sectional, so direction is unknown: depression itself can delay sleep timing, which is reverse causation. Heterogeneity was very high (I² 91.1% to 97.3%) [13].
Social jet lag linked to depression
Linked to more depressive symptoms with social jet lag in three meta-analyses, a weak correlation, with higher odds at 2 hours or more than at 1 to 2 hours.
The numbers and sources
- How common
- How often is not known: the sources give no rate.
- Effect
- Social jet lag correlated with depressive symptoms (r 0.049, 95% CI 0.044 to 0.054), explaining 0.24% of the variance, with no consistent link to anxiety [7]. In young people, 2 hours or more was linked to depressive symptoms (OR 1.44, 95% CI 1.18 to 1.77), and 1 to 2 hours was not significantly (OR 1.05, 95% CI 1.00 to 1.09) [8]. In adolescents and young people, 1 to 2 hours (OR 1.12, 95% CI 1.05 to 1.20) and over 2 hours (OR 1.87, 95% CI 1.73 to 2.02) were linked to depression, and social jet lag was also linked to anxiety [9].
- Population
- 25 observational studies [7]. 8 studies of people aged 10 to 24 [8]. 164,529 participants in 14 studies [9].
- Sources
- [7], [8], [9]
- Caveats
- Observational and mostly cross-sectional. The certainty of evidence was rated very low in one review [9]. Depressed mood can disturb sleep timing, which is reverse causation.
Social jet lag linked to higher body weight
Linked to higher body mass index, body fat and waist size with more social jet lag in two meta-analyses, small correlations with very high heterogeneity.
The numbers and sources
- How common
- How often is not known: the sources give no rate.
- Effect
- Social jet lag was positively linked to body mass index (r 0.12, 95% CI 0.07 to 0.17), fat mass (r 0.10), percent body fat (r 0.37) and waist circumference (r 0.15), and to higher odds of overweight or obesity (OR 1.20, p = 0.039) [14]. Against under 1 hour, 2 hours or more was linked to metabolic syndrome (OR 1.52) and a larger waist (mean difference 2.17 cm, 95% CI 0.61 to 3.73). Systolic blood pressure was 3.52 mmHg lower (95% CI -6.41 to -0.64) [15].
- Population
- 231,648 participants in 43 observational studies [14]. 16 studies, 5 pooled, 2 to 3 studies per outcome [15].
- Sources
- [14], [15]
- Caveats
- Observational. Heterogeneity was very high, I² up to 98.25% [14]. The second review pooled very few studies [15]. Weight gain can disturb sleep, which is reverse causation.
Evening chronotype linked to diabetes and blood sugar
Linked to 30% higher odds of diabetes in evening types in one meta-analysis and one large cohort, with higher blood glucose and HbA1c in cross-sectional data.
The numbers and sources
- How common
- How often is not known: the sources give no rate.
- Effect
- Evening types had higher odds of diabetes (OR 1.30, 95% CI 1.20 to 1.41), higher blood glucose (mean difference 7.82) and glycated hemoglobin (mean difference 7.64), higher LDL cholesterol (13.69) and triglycerides (12.62) than morning types, in cross-sectional studies [6]. In UK Biobank, definite evening types had more diabetes at enrollment than definite morning types (OR 1.30, 95% CI 1.24 to 1.36) [16].
- Population
- 377,797 participants in 39 studies [6]. 433,268 adults aged 38 to 73 [16].
- Sources
- [6], [16]
- Caveats
- Observational and cross-sectional, measured once, so these are differences between groups, not changes. The abstract gives the mean differences without units [6].
Irregular and late sleep linked to cardiometabolic risk
Linked to higher body mass index, insulin resistance, high blood pressure and heart events with irregular sleep timing in two systematic reviews that did not pool results.
The numbers and sources
- How common
- How often is not known: the sources give no rate.
- Effect
- Consistent, moderate-certainty evidence linked more irregular sleep timing to higher depressive and anxiety symptoms, higher body mass index, insulin resistance, hypertension and new cardiovascular events [18]. Later sleep timing and greater sleep variability were generally linked to adverse health outcomes, and weekend catch-up sleep to better ones, with evidence rated very low to moderate [19].
- Population
- 59 studies of adults [18]. 92,340 adults in 41 studies from 14 countries [19].
- Sources
- [18], [19]
- Caveats
- Observational. Neither review pooled effect sizes, because measures varied. Most associations were linear, so no threshold for late or irregular could be set [19].
Sleep onset time linked to heart disease
One large cohort linked falling asleep before 10 p.m., between 11 and midnight, or after midnight to 12% to 25% more cardiovascular disease than 10 to 11 p.m.
The numbers and sources
- How common
- How often is not known: the sources give no rate.
- Effect
- Against sleep onset at 10:00 to 10:59 p.m., hazard ratios for cardiovascular disease were 1.24 (95% CI 1.10 to 1.39) before 10 p.m., 1.12 (95% CI 1.01 to 1.25) at 11:00 to 11:59 p.m. and 1.25 (95% CI 1.02 to 1.52) at midnight or later, after adjusting for sleep duration and irregularity. The link was stronger in women [12].
- Population
- 103,712 UK Biobank participants with 7 days of wrist accelerometry, 3,172 cases over a mean 5.7 years [12].
- Sources
- [12]
- Caveats
- One observational cohort with one week of measurement. In men, only sleep onset before 10 p.m. was significant [12].
Evening chronotype linked to death from any cause
One large cohort linked being a definite evening type to 10% higher death from any cause than being a definite morning type.
The numbers and sources
- How common
- How often is not known: the sources give no rate.
- Effect
- Definite evening types had higher mortality than definite morning types (HR 1.10, 95% CI 1.02 to 1.18). Each step toward eveningness was linked to a small rise in death (HR 1.02) and cardiovascular death (HR 1.04, 95% CI 1.00 to 1.09) [16].
- Population
- 433,268 UK Biobank adults aged 38 to 73, mean follow-up 6.5 years, 10,534 deaths [16].
- Sources
- [16]
- Caveats
- One observational cohort with chronotype from a single question. Analyses adjusted for smoking, weight, sleep duration and illness, but residual confounding remains.
Mixed results2
Evening chronotype and cancer
Mixed results: one meta-analysis linked evening chronotype to 18% higher odds of cancer, and a systematic review of 22 studies found no consistent link for late timing.
The numbers and sources
- How common
- How often is not known: the sources give no rate.
- Effect
- Evening types had higher odds of cancer (OR 1.18, 95% CI 1.08 to 1.30) [6]. A review of 22 studies of chronotype, social jet lag, sleep midpoint and weekend catch-up sleep found no consistent evidence linking late timing to cancer [17].
- Population
- 377,797 participants in 39 studies [6]. 22 studies, 95% using self-report questionnaires, mostly of site-specific cancers [17].
- Sources
- [6], [17]
- Caveats
- Observational. Measures of timing varied widely [17].
Irregular sleep and death from any cause
Mixed results: the least regular sleepers had 20% to 88% higher death rates in several cohorts, but a meta-analysis found day-to-day rhythm stability not linked to death.
The numbers and sources
- How common
- How often is not known: the sources give no rate.
- Effect
- Against the least regular fifth, the more regular four fifths had 20% to 48% lower death from any cause, 16% to 39% lower cancer death and 22% to 57% lower cardiometabolic death, and regularity predicted death more strongly than sleep duration [10]. Five low-bias cohorts showed 20% to 88% higher mortality in the least regular sleepers [18]. In a meta-analysis of rest and activity rhythms, interdaily stability was not linked to any outcome, while more fragmented rhythms (HR 1.05) and lower amplitude (HR 1.46) were linked to death [11].
- Population
- 60,977 UK Biobank participants, mean age 62.8, followed about 6.3 years with 1,859 deaths [10]. 59 studies [18]. 109,365 participants in 7 studies [11].
- Sources
- [10], [18], [11]
- Caveats
- Observational. Illness and frailty disrupt sleep schedules, which is reverse causation. The measures of regularity differ between these sources [18][11].
Claims tested and not found
- That evening types eat more. In a meta-analysis of 39 studies, energy intake did not differ between morning and evening types [6].
- That evening types have higher blood pressure. The same meta-analysis found no difference in blood pressure or hypertension risk [6].
- That steadier day-to-day rest and activity rhythms are linked to longer life. In a meta-analysis of 7 studies, interdaily stability showed no significant link with death or heart disease [11].
Related
Sources
- Facer-Childs ER, Middleton B, Skene DJ, Bagshaw AP. Resetting the late timing of 'night owls' has a positive impact on mental health and performance. Sleep Medicine. 2019. https://doi.org/10.1016/j.sleep.2019.05.001
- Marx R, Tanner-Smith EE, Davison CM, et al. Later school start times for supporting the education, health, and well-being of high school students. Cochrane Database of Systematic Reviews. 2017. https://doi.org/10.1002/14651858.CD009467.pub2
- Minges KE, Redeker NS. Delayed school start times and adolescent sleep: A systematic review of the experimental evidence. Sleep Medicine Reviews. 2016. https://doi.org/10.1016/j.smrv.2015.06.002
- Wang RC, Lee MI, Aroul GS, et al. Delayed school start times to improve sleep duration and mitigate depression in adolescents: a systematic review and meta-analysis. Journal of Clinical Sleep Medicine. 2026. https://doi.org/10.1007/s44470-026-00116-5
- Au J, Reece J. The relationship between chronotype and depressive symptoms: A meta-analysis. Journal of Affective Disorders. 2017. https://doi.org/10.1016/j.jad.2017.04.021
- Lotti S, Pagliai G, Colombini B, Sofi F, Dinu M. Chronotype Differences in Energy Intake, Cardiometabolic Risk Parameters, Cancer, and Depression: A Systematic Review with Meta-Analysis of Observational Studies. Advances in Nutrition. 2022. https://doi.org/10.1093/advances/nmab115
- Gao L, Gao J, Zeng Z. Social jet lag and mental health outcomes: A systematic review and meta-analysis. Acta Psychologica. 2025. https://doi.org/10.1016/j.actpsy.2025.105419
- Sun S, Yang Y, Yu F, et al. Social jetlag and depressive symptoms among young people: a systematic review and meta-analysis. BMC Psychiatry. 2025. https://doi.org/10.1186/s12888-025-07066-x
- Lu YA, Tsai PS. Associations of Social Jetlag With Depression and Anxiety in Adolescents and Young People: A Systematic Review and Meta-Analysis. Depression and Anxiety. 2026. https://doi.org/10.1155/da/5542425
- 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. https://doi.org/10.1093/sleep/zsad253
- Chang F, Xu J, Guo M, et al. Association Between Rest-Activity Rhythm and Cardiovascular Disease, Cardiovascular Mortality, and All-Cause Mortality: A Systematic Review and Meta-Analysis. Journal of the American Heart Association. 2026. https://doi.org/10.1161/JAHA.125.048656
- Nikbakhtian S, Reed AB, Obika BD, et al. Accelerometer-derived sleep onset timing and cardiovascular disease incidence: a UK Biobank cohort study. European Heart Journal Digital Health. 2021. https://doi.org/10.1093/ehjdh/ztab088
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- Arab A, Karimi E, Garaulet M, Scheer FAJL. Social jetlag and obesity: A systematic review and meta-analysis. Obesity Reviews. 2024. https://doi.org/10.1111/obr.13664
- Lin MY, Kang YN, Apriliyasari RW, et al. Association Between Social Jetlag and Components of Metabolic Syndrome: A Systematic Review and Meta-Analysis. Journal of Nursing Research. 2024. https://doi.org/10.1097/jnr.0000000000000628
- Knutson KL, von Schantz M. Associations between chronotype, morbidity and mortality in the UK Biobank cohort. Chronobiology International. 2018. https://doi.org/10.1080/07420528.2018.1454458
- Donzella SM, Bryer BN, VoPham T, et al. Chronotype, sleep timing, sleep regularity, and cancer risk: A systematic review. Sleep. 2025. https://doi.org/10.1093/sleep/zsaf059
- Kalkanis A, Lenkens D, Steiropoulos P, Testelmans D. Sleep regularity as an important component of sleep hygiene: a systematic review. Sleep Medicine Reviews. 2025. https://doi.org/10.1016/j.smrv.2025.102203
- 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. https://doi.org/10.1139/apnm-2020-0032