Association of sleep timing with all-cause and cardiovascular mortality: the Sleep Heart Health Study and the Osteoporotic Fractures in Men Study

Study Objectives: Previous studies have highlighted the importance of sleep patterns for human health. This study aimed to investigate the association of sleep timing with all-cause and cardiovascular disease mortality. Methods: Participants were screened from two cohort studies: the Sleep Heart Health Study (SHHS; n = 4,824) and the Osteoporotic Fractures in Men Study (n = 2,658). Sleep timing, including bedtime and wake-up time, was obtained from sleep habit questionnaires at baseline. The sleep midpoint was defined as the halfway point between the bedtime and wake-up time. Restricted cubic splines and Cox proportional hazards regression analyses were used to examine the association between sleep timing and mortality. Results: We observed a U-shaped association between bedtime and all-cause mortality in both the SHHS and Osteoporotic Fractures in Men Study groups. Specifically, bedtime at 11:00 PM and waking up at 7:00 AM was the nadir for all-cause and cardiovascular disease mortality risks. Individuals with late bedtime (> 12:00 AM) had an increased risk of all-cause mortality in SHHS (hazard ratio 1.53, 95% confidence interval 1.28–1.84) and Osteoporotic Fractures in Men Study (hazard ratio 1.27, 95% confidence interval 1.01–1.58). In the SHHS, late wake-up time (> 8:00 AM) was associated with increased all-cause mortality (hazard ratio 1.39, 95% confidence interval 1.13–1.72). No significant association was found between wake-up time and cardiovascular disease mortality. Delaying sleep midpoint (> 4:00 AM) was also significantly associated with all-cause mortality in the SHHS and Osteoporotic Fractures in Men Study. Conclusions: Sleep timing is associated with all-cause and cardiovascular disease mortality. Our findings highlight the importance of appropriate sleep timing in reducing mortality risk.