Outdoor artificial light at night and cardiovascular disease in adults: a Chinese nationwide cohort study

Abstract Background Although the electric light is a significant promotion in the human progress and civilization, its adverse effects of outdoor artificial light at night (ALAN) are being extensively studied. However, the association of outdoor ALAN and cardiovascular disease (CVD) has never been confirmed in large nationwide studies, especially in urban areas with high exposure levels and in rural areas with low exposure levels, respectively. Purpose To explore the association between outdoor ALAN and CVD. Methods This national study enrolled 12,686 adults ≥ 40 years across China. The outdoor ALAN exposure (nW/cm2/sr) with the resolution of the 500 meters around each participant's location was obtained from satellite image data via Visible Infrared Imaging Radiometer Suite day-night band on board the Joint Polarorbiting Satellite System. CVD was defined by a doctor's record of diagnoses, including heart disease and stroke. Poisson regression model and restricted cubic spline models were used to estimate the relationship between outdoor ALAN and CVD in urban and rural areas, respectively. Subgroup analysis was also conducted using Poisson models for each subgroup. Results At a median follow-up of 7 years, 1,732 cases of CVD were identified. The mean age of the participants was 58 years and 49% were males. In urban areas, outdoor ALAN exposure at the highest quartile (Q4) increased the incidence of CVD among participants by 34% compared to those exposure at the lowest quartile (Q1) (incident rate ratio, IRR: 1.34,95% CI: 1.07—1.69, p = 0.01), adjusting for age, sex, BMI, education, smoke ever, alcohol consumption, physical activity and household consumption. In rural areas, compared with those at the Q1 of outdoor ALAN exposure, exposure at the Q4 reduced the incidence of CVD by 17% (IRR: 0.83, 95% CI: 0.70—0.98, p = 0.028) after full adjustment. Dose-response relationship indicated that outdoor ALAN levels were linearly associated with decreased CVD in rural area (p for non-linearity = 0.370), while the association between outdoor ALAN levels and CVD was shown as an inverse "U" shape in urban area (p for non-linearity ≤ 0.001). Subgroup analysis shown that the CVD risk of middle-aged people, people with history of alcohol consumption, or people with low levels of physical activity were susceptible to outdoor ALAN exposure. Conclusions Outdoor ALAN exposure was associated with the risk of CVD, which was heterogeneous with different levels of exposure range. In rural areas with low outdoor ALAN exposure settings, outdoor ALAN exposure was negatively correlated with the risk of developed CVD, while the association was reverse in urban areas with high outdoor ALAN exposure settings. We call for a reduction in the use of high-intensity ALAN and to pay attention to the effects of emotional, psychological, and biological changes associated with outdoor ALAN exposure on cardiovascular health.Figure 1