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

Objective: 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. Design: Systematic review and meta-analysis of prospective cohort studies. Setting and participants: Community or clinical settings. Participants included patients with dementia or Alzheimer's disease and the general population. Measures: 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. Results: 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). Conclusions and implications: 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. (C) 2019 Published by Elsevier Inc. on behalf of AMDA - The Society for Post-Acute and Long-Term Care Medicine.