Weekday and weekend sleep duration and mortality amongmiddle-to-older aged White and Black adults in a low-income southernUS cohort

Introduction
Both short and long sleep have been associated with higher mortality. However, most studies are conducted in predominantly White or Asian populations and little is known about the sleep-mortality relationship in Blacks. Given the high prevalence of short and long sleep in Blacks, it is important to examine the health effects of sleep in this population.

Methods
We studied sleep duration in relation to all-cause, cardiovascular and cancer mortality in 55,375 participants age 40ñ79 at enrollment in the Southern Community Cohort Study, of whom ?2/3 are Black. Weekday and weekend sleep durations were self-reported. Mortality follow up started at baseline (2002ñ2009) and was regularly updated until 2015 via linkage to Social Security Administration and the National Death Index. We used Cox proportional hazards model adjusting for multiple covariates to estimate relative risks associated with sleep duration.

Results
We found U-shaped relationships between weekday and weekend sleep duration and all-cause mortality, with the effects stronger in Whites than Blacks. Risks for all-cause mortality were significantly elevated by about 25% among Whites and about 10% among Blacks reporting either less than 5 hours or more than 9 hours of sleep compared with those reporting 8 hours of sleep. The associations among Whites but not Blacks were even stronger for cardiovascular disease mortality, whereas no association between sleep duration and cancer mortality was found in either group.

Conclusions
Our results suggest that short and long sleep durations may be weaker predictors of total and cardiovascular mortality in Blacks than in Whites.