Background: Evidence points to associations between sleep quality, dementia, and mortality. We examined whether poor sleep quality mediated or moderated the association between dementia and mortality risk among older US adults and vice versa, and whether these associations differed by sex and by race.
Methods: The study investigated bi-directional associations between sleep quality, dementia and mortality in older US adults using data from the Health and Retirement Study (N = 6,991, mean age = 78.1y, follow-up: 2006-2020, number of deaths = 4,938). It tested interactions and mediating effects, using Cox proportional hazards models and four-way decomposition models.
Results: Poor sleep quality was associated with increased mortality risk, particularly among male and White older adults. However, the association was reversed in the fully adjusted model, with a 7% decrease in risk per tertile. Probable dementia was associated with a two-fold increase in mortality risk, with a stronger association found among White adults. The association was markedly attenuated in the fully adjusted models. Sleep quality-stratified models showed a stronger positive association between dementia and mortality among individuals with better sleep quality. Both mediation and interaction were involved in explaining the total effects under study, though statistically significant total effects were mainly composed of controlled direct effects.
Conclusions: Poor sleep quality is directly related to mortality risk before lifestyle and health-related factors are adjusted. Dementia is linked to mortality risk, especially in individuals with better sleep quality, males, and White older adults. Future research should explore the underlying mechanisms.
Keywords: aging; cohort studies; dementia; mortality; sleep quality.