Outdoor artificial light at night and incident cardiovascular disease in adults: A national cohort study across China

Cardiovascular diseases (CVDs) become a major public health concern. Evidence concerning the effects of outdoor artificial light at night (ALAN) on CVD in adults is scarce. We aimed to investigate the extent to which outdoor ALAN could affect the risk of CVD over a exposure range. Data from the China Health and Retirement Longitudinal Study, a population-based longitudinal study, launched in 2011–2012 and follow up till 2018, covering 28 provinces, autonomous regions and municipalities across mainland China. This study included 14,097 adults aged ≥45 years. Outdoor ALAN exposure (in nanowatts per centimeters squared per steradian) within 500 m of each participant's baseline residence was obtained from satellite image data. CVD was defined from medical diagnosis. The population was divided into three groups based on outdoor ALAN exposure from low to high. Cox regression model was used to estimate the association between outdoor ALAN exposure and incident CVD with hazard ratios (HRs) and 95 % confidence intervals (CIs). The mean (SD) age of the cohort was 57.6 (9.1) years old and 49.3 % were males. Outdoor ALAN exposure of study participants ranged from 0.02 to 39.79 nW/cm²/sr. During 83,033 person-years of follow-up, 2190 (15.5 %) cases of CVD were identified. Both low (HR: 1.21; 95 % CI: 1.02—1.43) and high (HR: 1.23; 95 % CI: 1.04—1.46) levels of outdoor ALAN exposure group were associated with higher risk of CVD compared with intermediate levels of outdoor ALAN exposure group. Body mass index was a significant effect modifier in the association between outdoor ALAN and risk of CVD, with stronger effects among those who was overweight or obese. The findings of this study suggest that low and high outdoor ALAN exposure were associated with a higher risk for CVD. More attention should be given to the cardiovascular effects associated with outdoor ALAN exposure.