Sleep Characteristics and Daytime Cortisol Levels in Older Adults.

Objective: Older adults frequently report sleep problems and are at increased risk of cardiometabolic disruption. Experimental sleep restriction of younger adults has suggested that cortisol may be on the pathway between sleep restriction and cardiometabolic disease. We investigated whether the natural variation in sleep among older adults is associated with daytime cortisol level.

Methods: Salivary cortisol samples and actigraphy sleep data were collected from a random subsample of participants in the National Social Life, Health and Aging Project, a nationally representative probability sample of adults aged 62-90 (N = 672). Salivary cortisol was measured with 3 timed samples at the beginning, middle, and end of a 2-hr in-home interview. Sleep characteristics were derived from wrist actigraphy (fragmentation, wake after sleep onset [WASO], and duration) and from survey responses about usual sleep duration and sleep problems. For each individual, a single summary daytime cortisol level was estimated by fitting a marginal longitudinal model for the 3 time-stamped cortisol samples. The resulting estimates were then regressed on each sleep measure, adjusting for sociodemographics, health behaviors, and comorbidities.

Results: From actigraphy, both higher fragmentation score (β = 0.02; 95% confidence interval [CI] = 0.00 to 0.03) and longer WASO (β = 0.27; 95% CI = 0.04 to 0.51) were significantly associated with higher daytime cortisol; sleep duration was not. Self-reported sleep duration and sleep problems were also not associated with cortisol.

Conclusion: Actigraph measures of sleep disturbance are associated with higher daytime cortisol among older adults. However, cross-sectional data cannot distinguish causal direction or whether cortisol and sleep disruption have a common cause.