Associations between wearable device-measured sleep variability and cognition among older adults

Healthy sleep habits are protective against adverse health outcomes, but it is unclear how strongly sleep intraindividual variability is associated with cognitive function among older adults. In this study we aimed to examine how accelerometer-derived intraindividual variability in sleep duration, efficiency, onset timing, and offset timing is associated with cognition using cross-sectional data from the 2011-2014 waves of the National Health and Nutrition Examination Survey (NHANES). Cognition was assessed by creating a composite measure derived by summing z-scores from the Digit Symbol Substitution Test (DSST), Consortium to Establish a Registry for Alzheimers Disease Word-Learning subtest (CERAD-WL), and the Animal Fluency Test (AFT). A final cohort of 2508 older adults aged 60+ with at least three days of accelerometer wear time who completed all three cognitive tests were included in this study. After centering all sleep intraindividual variability metrics and adjusting for demographic factors, the presence of diabetes, depressive symptoms, and measures of functional independence, we found that increased intraindividual variability in sleep onset timing was associated with worse cognition (Beta, -0.12; 95% CI, -0.19 to -0.05), as was increased intraindividual variability in sleep efficiency (Beta, -0.12; 95% CI, -0.20 to -0.05), and increased interindividual variability in sleep duration (Beta, -0.10; 95% CI, -0.17 to -0.03). This study suggests that sleep guidance aimed at preserving cognition among older adults could be revised to include a focus on sleep consistency regarding onset timing, quality, and duration.