Sleep duration and risk of all-cause mortality: A flexible, non-linear, meta-regression of 40 prospective cohort studies.
Level 3 - non-randomized controlled study
Meta-analysis of prospective observational cohort studies
PubMed 27067616 · doi:10.1016/j.smrv.2016.02.005
What was done
A systematic review and non-linear dose-response meta-regression using restricted cubic splines evaluated the association between sleep duration and all-cause mortality in adults. Medline, Embase, EBSCOhost-PsycINFO, and EBSCOhost-CINAHL Plus databases were searched through November 29, 2015. Eligible studies were prospective cohort studies assessing adult sleep duration in at least three categories and reporting all-cause mortality.
What was found
The meta-analysis included 40 cohort studies enrolling 2,200,425 participants with 271,507 deaths. A J-shaped association with all-cause mortality was observed relative to 7 hours of daily sleep (p < 0.01 for non-linearity, 29 cohorts). Short sleep increased mortality risk: 4 hours (RR = 1.05; 95% CI: 1.02-1.07), 5 hours (RR = 1.06; 95% CI: 1.03-1.09), and 6 hours (RR = 1.04; 95% CI: 1.03-1.06). Prolonged sleep had steeper risk increases: 8 hours (RR = 1.03; 95% CI: 1.02-1.05), 9 hours (RR = 1.13; 95% CI: 1.10-1.16), 10 hours (RR = 1.25; 95% CI: 1.22-1.28), and 11 hours (RR = 1.38; 95% CI: 1.33-1.44). For night-only sleep (13 cohorts), prolonged sleep increased mortality at 9 hours (RR = 1.08; 95% CI: 1.05-1.11) and 10 hours (RR = 1.24; 95% CI: 1.21-1.28). In subgroup analysis, short sleep (<7 h) increased mortality in females (4 hours: RR = 1.07; 95% CI: 1.02-1.13) but not in males (4 hours: RR = 1.01; 95% CI: 0.96-1.06).
Why it matters
This large meta-regression establishes 7 hours of daily sleep as the nadir for all-cause mortality risk, showing that prolonged sleep has a stronger association with increased mortality than short sleep.
Limits
The findings derive entirely from observational cohort studies, preventing causal inference. Sleep duration was typically self-reported, and residual confounding from underlying subclinical disease or depression cannot be ruled out.
Cited by
- supports Sleeping fewer than 7 hours per night or more than 10 hours per night is associated with increased all-cause mortality compared to sleeping 7 to 9 hours.