BACKGROUND: As the primary circadian entrainer, light may affect cardiovascular health through circadian disruption or enhancement, depending on its timing. Epidemiologic studies on the associations of daytime and nighttime light exposures with cardiovascular disease (CVD) risk are limited and have examined these exposures separately, yielding contradictory findings.
OBJECTIVES: We aimed to examine the association between the distinction between daytime and nighttime light exposure and CVD mortality risk.
METHODS: This population-based retrospective cohort study included 7,607 adults from the U.S. National Health and Nutrition Examination Survey (2011-2014) who wore an accelerometer with a light sensor for a week. CVD mortality data were obtained through linkage to the National Death Index until 2019. We estimated differences in time between daytime light exposure above 1000 lux versus nighttime light exposure above 1 lux. We used Cox models to estimate hazard ratios (HRs) for CVD mortality, adjusting for physical activity, sleep duration, chronotype, serum 25(OH)D, and other covariates.
RESULTS: The study population (46.8% male, 67.9% non-Hispanic White) had a baseline mean age of 49.4 years (SE, 0.4). Over a median follow-up of 6.8 years, 233 CVD deaths occurred. Greater differences in daytime versus nighttime light exposure were associated with a lower CVD mortality risk in a linear dose-response pattern (per 1-hour increment: HR, 0.88 [95% CI, 0.78-0.98]; Pnonlinearity=0.92). The association showed no evidence of heterogeneity by age or sex.
CONCLUSIONS: Greater distinctions between daytime and nighttime light exposure were associated with lower cardiovascular disease mortality among U.S. adults.
