Abstract
A dose-response meta-analysis was conducted to summarize evidence from prospective cohort studies about the association of nighttime sleep duration and 24-hour sleep duration with risk of all-cause mortality among adults. Pertinent studies were identified by a search of Embase and PubMed databases to March 2015. A two-stage random-effects dose–response meta-analysis was used to combine study-specific relative risks and 95% confidence intervals [RRs (95% CIs)]. Thirty-five articles were included. Compared with 7 hours/day, the RRs (95% CIs) of all-cause mortality were 1.07 (1.03–1.13), 1.04 (1.01–1.07), 1.01 (1.00–1.02), 1.07 (1.06–1.09), 1.21 (1.18–1.24), 1.37 (1.32–1.42) and 1.55 (1.47–1.63) for 4, 5, 6, 8, 9, 10 and 11 hours/day of nighttime sleep, respectively (146,830 death cases among 1,526,609 participants), and the risks were 1.09 (1.04–1.14), 1.05 (1.02–1.09), 1.02 (1.00–1.03), 1.08 (1.05–1.10), 1.27 (1.20–1.36), 1.53 (1.38–1.70) and 1.84 (1.59–2.13) for 4, 5, 6, 8, 9, 10 and 11 hours/day of 24-hour sleep, respectively (101,641 death cases among 903,727 participants). The above relationships were also found in subjects without cardiovascular diseases and cancer at baseline, and other covariates did not influence the relationships substantially. The results suggested that 7 hours/day of sleep duration should be recommended to prevent premature death among adults.
Highlights
Results from 25 articles with 36 results were used including 146,830 deaths among 1,526,609 participants
Other factors did not contribute to the heterogeneity significantly. Results from this dose-response meta-analysis showed that, compared with 7 hours/day, sleep duration was associated with the risk of all-cause mortality in a U-shaped manner among adults, regardless of nighttime sleep or 24-hour sleep
Five theoretical pathways for the relationship between short sleep duration and mortality have been put forth[32]: (I) short sleep directly causes mortality itself; (II) short sleep may result from variety of social, environmental, and physiological changes that lead to increased mortality risk; (III) short sleep itself causes physiological and social outcomes that may lead to increased mortality; (IV) short sleep is associated with other characteristics causally linked to mortality, such as age; and (V) the possibility of reverse causality is of concern
Summary
In the analysis of nighttime sleep duration and risk of all-cause mortality, follow-up duration, sleep duration assessment method, mean age, sex, continent where the study were conducted, covariates adjusted for and study quality did not contribute to the heterogeneity significantly (all P values > 0.05). In the analysis of 24-hour sleep duration and all-cause mortality, continent where the study were conducted (P = 0.05) and follow-up duration (P = 0.05) might contribute to the heterogeneity, which may be caused by chance because of the relatively small number of studies. Other factors did not contribute to the heterogeneity significantly (all P values > 0.05)
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