Moderators and mediators of exercise-induced objective sleep improvements in midlife and older adults with sleep complaints.

OBJECTIVE: Exercise can improve sleep quality, but for whom and by what means remains unclear. We examined moderators and mediators of objective sleep improvements in a 12-month randomized controlled trial among underactive midlife and older adults reporting mild/moderate sleep complaints. METHODS: Participants (N = 66, 67% women, 55-79 years) were randomized to moderate-intensity exercise or health education control. Putative moderators were gender, age, physical function, self-reported global sleep quality, and physical activity levels. Putative mediators were changes in BMI, depressive symptoms, and physical function at 6 months. Objective sleep outcomes measured by in-home polysomnography were percent time in Stage I sleep, percent time in Stage II sleep, and number of awakenings during the first third of sleep at 12 months. RESULTS: Baseline physical function and sleep quality moderated changes in Stage I sleep; individuals with higher initial physical function (p = .01) and poorer sleep quality (p = .03) had greater improvements. Baseline physical activity level moderated changes in Stage II sleep (p = .04) and number of awakenings (p = .01); more sedentary individuals had greater improvements. Decreased depressive symptoms (CI:-1.57 to -0.02) mediated change in Stage I sleep. Decreased depressive symptoms (CI:-0.75 to -0.01), decreased BMI (CI:-1.08 to -0.06), and increased physical function (CI: 0.01 to 0.72) mediated change in number of awakenings. CONCLUSIONS: Initially less active individuals with higher initial physical function and poorer sleep quality improved the most. Affective, functional, and metabolic mediators specific to sleep architecture parameters were suggested. These results indicate strategies to more efficiently treat poor sleep through exercise in older adults.