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: Fifteen studies with 65 501 participants were recruited. Excessive daytime sleepiness was associated with increased risk of cognitive decline and all-cause dementia (risk ratio 1.26, 95% confidence interval [CI]: 1.13-1.41, and risk ratio 1.68, 95% CI: 1.07-2.66, respectively). Long sleep duration increased the risk of all-cause dementia by 29% (95% hazard ratio CI: 0.94-1.77, Pr [hazard ratio > 1] = 0.94); and cognitive decline by 13% (95% risk ratio, 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 < 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.
Keywords: Cognition; Daytime sleepiness; Dementia; Sleep hours.
© The Author(s) 2025. Published by Oxford University Press on behalf of the Gerontological Society of America.