Association Between Outdoor Light at Night and Risk of Coronary Heart Disease among 60,229 Older Adults: A Prospective Cohort Study

Abstract

Background Light at night (LAN) is the most important environmental cue for circadian misalignment, which may increase risk of coronary heart disease through impairing circadian rhythms. We aimed to estimate the association between exposure to outdoor LAN and coronary heart disease (CHD) in elders.MethodsWe followed 60,229 Hong Kong elders free of CHD from 1998 through 2011. Annual LAN exposure was estimated using time-varying satellite data for a composite of persistent nighttime illumination at ~1 km2 scale for each residence. We used Cox proportional hazard models to calculate hazard ratios (HRs) and 95% confidence intervals (CIs) for the association between exposure to outdoor LAN and risk of CHD. Results Over 10 to 13 years of follow-up, we identified 3,772 incident CHD cases and 1,695 CHD deaths. Annual levels of LAN at participants’ residential addresses ranged from 2.2 to 233.1 nW/cm2/sr. The concentration-response functions for the association between LAN and CHD incidence and mortality were approximate linear with the slopes becoming flat when LAN above 110 nW/cm2/sr. Per interquartile range (IQR) (60.0 nW/cm2/sr) increase in outdoor LAN, the HR was 1.09 (95% CI: 1.03, 1.17) for CHD incidence and 1.10 (95% CI: 1.01, 1.22) for CHD mortality after adjusting for both individual and area-level risk factors.Conclusions Exposure to outdoor light at night was associated with higher risk of coronary heart disease among Hong Kong elders. Our findings highlight the need to regulate light pollution for the potential coronary heart disease benefits.