Air pollution, greenness and risk of overweight among middle-aged and older adults: A cohort study in China.

BACKGROUND: Exposure to air pollution may increase the risk of obesity, but living in greener space may reduce this risk. Epidemiological evidence, however, is inconsistent. METHODS: Using data from the China Health and Retirement Longitudinal Study (2011-2015), we conducted a nationwide cohort study of 7424 adults. We measured overweight/obesity according to body mass index. We used annual average ground-level air pollutants, including ozone (O3), nitrogen dioxide (NO2), and particulate matter with aerodynamic diameters ≤2.5 µm (PM2.5), to demonstrate air pollution levels. We used the Normalized difference vegetation index (NDVI) to measure greenness exposure. We used time-varying Cox proportional hazard regression models to analyze the connections among air pollution, greenness, and the development of overweight/obesity in middle-aged and older adults in China. We also conducted mediation analyses to examine the mediating effects of air pollution. RESULTS: We found that lower risk of overweight/obesity was associated with more greenness exposure and lower levels of air pollution. We identified that an interquartile increment in NDVI was correlated with a lower hazard ratio (HR) of becoming overweight or obese (HR = 0.806, 95% confidence interval [CI]: 0.754-0.862). Although a 10 µg/m3 increase in PM2.5 and NO2 was correlated with higher risks (HR = 1.049, 95% CI = 1.022-1.075, HR = 1.376, 95% CI = 1.264-1.499). Effects of PM2.5 on being overweight or obese were stronger in men than in women. According to the mediation analysis, PM2.5 and NO2 mediated 8.85% and 19.22% of the association between greenness and being overweight or obese. CONCLUSIONS: An increased risk of being overweight or obese in middle-aged and older adults in China was associated with long-term exposure to higher levels of PM2.5 and NO2. This risk was reduced through NDVI exposure, and the associations were partially mediated by air pollutants. To verify these findings, fine-scale studies are needed.