Effect of Excessive daytime sleepiness and long sleep duration on all cause dementia: a systematic review and meta-analysis

Background Excessive daytime sleepiness (EDS) and long sleep duration are common in older adults and are related to dementia pathology. This study aims to assess the effect of EDS and long sleep duration on all-cause dementia and cognitive decline. Methods We identified longitudinal studies assessing the relationship between EDS and/or long sleep duration on cognitive decline/dementia published up to March 24, 2024 from MEDLINE, Embase, PsyINFO, the Cochrane Central Register of Controlled Trials, and PubMed. The inverse-variance-weighted average method and Bayesian multilevel regression models were used to test the effect of EDS and long sleep duration on cognitive decline and dementia risk. Results 15 studies with 65501 participants were recruited. EDS was associated with increased risk of cognitive decline and all-cause dementia (Risk Ratio (RR)1.26, 95% Confidence Interval (CI) 1.13-1.41, and RR 1.68, 95% CI 1.07-2.66, respectively). Long sleep duration increased the risk of all-cause dementia by 29% (95% Hazard Ratio (HR) CI: 0.94 - 1.77, Pr (HR>1) = 0.94); and cognitive decline by 13% (95% RR CI: 0.92 - 1.4). Dementia-free time at age 85 was 0.13 years shorter among long sleepers (Pr (∆Restricted Mean Dementia-Free Time (RMDFT) < 0) = 0.98). Conclusions Both EDS and long sleep duration were associated with increased risk of all-cause dementia. However, it remains unclear whether these are independent risk factors or merely reflect the same underlying pathological process. Further studies are needed to explore the interaction between these exposures on dementia and their potential as targets for dementia prevention.