Sleep Timing, Sleep Timing Regularity, and Cognitive Performance in Women Entering Late Adulthood: The Study of Women's Health Across the Nation (SWAN)

This study examined whether sleep timing and its regularity are associated with cognitive performance in older women and whether associations vary based on cardiometabolic risk factors. The cross-sectional analysis included 1,177 community-dwelling females (mean age 65 years) from the observational Study of Women's Health Across the Nation (SWAN) annual visit 15. Sleep timing (mean midpoint from sleep onset to wake-up) and its regularity (standard deviation of midpoint ) were assessed using actigraphy. Cognitive measures included immediate and delayed verbal memory, working memory, and processing speed. Cardiometabolic risk measures included central obesity, hypertension, diabetes, and the Atherosclerotic Cardiovascular Disease (ASCVD) risk score. Linear regression models, adjusted for covariates, tested associations between sleep and cognitive measures. After covariate adjustment, early sleep timing was associated with worse delayed verbal memory (β = -0.37; p = 0.047) and late sleep timing was associated with worse processing speed (β = -1.80; p = 0.008). Irregular sleep timing was associated with worse immediate (β = -0.29; p = 0.020) and delayed verbal memory (β = -0.36; p= 0.006), and better working memory (β = 0.50; p = 0.004). Associations between early sleep timing and delayed verbal memory strengthened as ASCVD risk increased (interaction β=-8.83, p=.026), and tsleep timing irregularity's effect on-working memory was stronger among women with hypertension (interaction β = -3.35, p = .039). Sleep timing and its regularity are concurrently associated with cognitive performance in older women. Cardiovascular disease risk may modify some of these associations. Future longitudinal studies are needed to clarify these relationships.