Association of daytime napping and nighttime sleep with all-cause mortality: A prospective cohort study of China Health and Retirement Longitudinal Study

Study objectives: The correlation of daytime napping and nighttime sleep duration on mortality was inconsistent. We aimed to explore their separate links to all-cause/premature mortality, and evaluate their combined impact on all-cause mortality risk. Methods: All of 20617 (mean age: 56.90 +/- 10.19, 52.18 % females) participants from China Health and Retirement Longitudinal Study were followed for a median of 7 years (interquartile range: 4-7) to detect death status. Baseline self-reported napping and sleep duration was categorized: napping as none, <60 min, 60-90 min, and >= 90 min, sleep as <6 h/night, 6-8 h/night, and >= 8 h/night. Death event was tracked, and premature death was defined using 2015 China's average life expectancy (73.64 years for men, and 79.43 years for women). Cox regression models analyzed the data. Results: During follow-up, 1621 participants (7.86 %) died, including 985 (4.78 %) premature deaths. Compared to none nappers, napping >= 90 min associated with a higher risk of all-cause mortality (Hazard ratio, [HR] 1.23, 95 % confidence interval [CI] 1.06-1.42) and premature mortality (HR 1.23, 95 % CI 1.02-1.49), while napping <60 min correlated with a lower risk of premature mortality (HR 0.71, 95 % CI 0.54-0.95), after adjustment. Compared to sleep 6-8 h/night, nighttime sleep >= 8 h was associated with an increased risk of all-cause mortality (HR 1.20, 95 % CI 1.04-1.37) and premature mortality (HR 1.28, 95 % CI 1.08-1.52). Participants napping >= 90 min and sleeping >= 8 h had a multi-adjusted HR (95%CI) of 1.50 (95 % CI 1.17-1.92) for all-cause mortality, versus no napping and 6-8 h/night sleep. Conclusions: Prolonged napping and extended nighttime sleep linked to increased mortality risk, particularly in combination. Optimizing sleep patterns may have potential implication in mortality prevention.