Optimal sleep timing revealed: a new perspective on reducing all-cause mortality and cardiovascular diseases-cause mortality in older adults.

Study objectives: In addition to sleep duration, sleep timing is another important but severely understudied sleep characteristic that may closely associated with the cardiovascular disease (CVD) mortality. To investigate the optimal sleep timing, we assessed the associations of sleep timing with all-cause and CVD mortality in large older adults.

Methods: This prospective cohort study included 18,129 adults (median age=65 years) from Guangzhou Biobank Cohort Study (GBCS), recruited during 2008-2012 and followed up until July 2022. Participants' sleep timing (early, intermediate and late) were defined by the midpoint between bedtime and wake time. Four CVD susceptibility single-nucleotide polymorphism (SNPs) were used to calculate the genetic risk score.

Results: During a median follow-up of 12.4 years with 213,534 person-years, 2,997 deaths occurred. Compared with the intermediate group, both early and late midpoint groups were associated with higher risk of all-cause mortality (adjusted hazard ratio (AHR)=1.18, 95% CI 1.07-1.30 and 1.13, 1.01-1.26). Restricted cubic spline curves indicate U-shaped associations of sleep midpoint, bedtime and wake time with all-cause and CVD mortality (all P for non-linearity<0.05), with the lowest risk observed at approximately 2:30 AM, 11:00 PM and 6:00 AM, respectively. The associations of early and late sleep timing with risk of all-cause mortality were more pronounced in men, older people and those with high CVD genetic risk score.

Conclusions: For the first time, we identified U-shaped associations of sleep timing with all-cause and CVD mortality by identifying the specific sleep timing points associated with the lowest mortality risk, explicitly from 11:00 PM to 6:00 AM.