Sleep Duration and the Risk of Dementia: A Systematic Review and Meta-analysis of Prospective Cohort Studies

Epidemiologic studies have reported inconsistent findings about the association between sleep duration and the risk of dementia. We aimed to clarify this association by method of meta-analysis.Systematic review and meta-analysis of prospective cohort studies.Community or clinical settings. Participants included patients with dementia or Alzheimer's disease and the general population.We systematically searched the PubMed, EMBASE, and Web of Science for prospective cohort studies investigating the association between sleep duration and all-cause dementia or Alzheimer's disease (AD). Generic inverse-variance method was used to combine the outcomes with a random effects model for the association between sleep duration (short or long vs normal) and all-cause dementia or AD.We identified 7 studies for all-cause dementia and 6 studies for AD. Pooled analyses showed that long sleep duration was associated with a 77% increased risk of all-cause dementia [hazard ratio (HR) = 1.77, 95% confidence interval (CI) = 1.32-2.37] and a 63% increased risk of AD (HR = 1.63, 95% CI = 1.24-2.13). Short sleep duration was not statistically associated with an increased risk of all-cause dementia (HR = 1.20, 95% CI = 0.91-1.59) or AD (HR = 1.18, 95% CI = 0.91-1.54).Only long sleep duration is significantly associated with an increased risk of all-dementia and AD. Future studies are needed to better understand the mechanisms underlying this association.