Sex- and age-specific association between outdoor light at night and obesity in Chinese adults: A national cross-sectional study of 98,658 participants from 162 study sites

BackgroundExposure to light at night (LAN) is a potent disruptor of the circadian system. Whether LAN exposure exerts a sex- or age-specific influence on obesity needs investigation. ObjectivesTo estimate the sex- and age-specific associations of exposure to outdoor LAN and obesity based on a national and cross-sectional survey. MethodsThe study included a nationally representative sample of 98,658 adults aged >= 18 years who had lived in their current residence for >= 6 months from 162 study sites across mainland China in 2010. Outdoor LAN exposure was estimated from satellite imaging data. General obesity was defined as body-mass index (BMI) >= 28 kg/m(2) and central obesity was defined as waist circumference >= 90 cm in men and >= 85 cm in women. Linear and logistic regression models were used to examine the associations between LAN exposure and prevalent obesity in sex and age categories. ResultsA monotonically increasing association of outdoor LAN with BMI, waist circumference was observed in all sex and age categories, except for adults aged 18-39 years. Significant associations of LAN exposure with prevalent obesity were observed in each sex and age category, especially in men and older people. Per 1-quintile increase in LAN was associated with 14% increased odds of general obesity in men (odds ratio, OR=1.14, 95% confidence interval, CI=1.07-1.23) and 24% in adults aged >= 60 years (OR=1.24, 95% CI=1.14-1.35). Per 1-quintile increase in LAN was associated with 19% increased odds of central obesity in men (OR=1.19, 95% CI=1.11-1.26) and 26% in adults aged >= 60 years (OR=1.26, 95% CI=1.17-1.35). ConclusionsIncreased chronic outdoor LAN exposure was associated with increased prevalence of obesity in sex- and age- specific Chinese populations. Public health policies on reducing light pollution at night might be considered in obesity prevention.