Residential greenness and air pollution mortality using the Chinese Longitudinal Healthy Longevity Survey: a longitudinal analysis

Abstract

BackgroundBoth air pollution and green space have been shown to independently affect mortality. We aimed to study whether greenness might interact with air pollution-related mortality among Chinese adults aged 65 years and older. MethodsWe used the 2008 wave of the Chinese Longitudinal Healthy Longevity Survey, with participants surveyed in 2012 and 2014. We used satellite remote sensing around participants' residential addresses to calculate our exposure variables. Normalized Difference Vegetation Index (NDVI) within a 500 m radius around their residence was used to measure contemporaneous NDVI (value at the time closest to the outcome event). Concentrations of particulate matter (PM2·5) were calculated using the 3-year average in a 1 km × 1 km grid. Cox proportional hazards models were used to estimate the effects of NDVI, PM2·5, and their interaction on all-cause mortality. We controlled for age, sex, ethnicity, marital status, geographic region, urban or rural residence, education, occupation, financial support, social and leisure activity, smoking status, alcohol consumption, and physical activity. We also stratified analysis by sex, urban or rural regions, smoking status, and exercise status. FindingsWe followed up 12 873 participants, totalling 47 884 person-years. There were 7426 mortality events from 2008 to 2014. At baseline, the mean age was 87 years (SD 11·34) and 84·62% lived in a rural area. The mean contemporaneous NDVIs were 0·42 (SD 0·21); the mean PM2·5 concentration was 49·63 μg/m3 (SD 13·72). In the fully adjusted model, the mortality hazard ratios (HRs) for each 0·1-unit decrease in contemporaneous NDVI was 1·08 (95% CI 1·03–1·13), each 10 μg/m3 increase in PM2·5 was 1·13 (1·09–1·18), interaction term 1·01 (1·00–1·02) with statistical significance (p=0·027). In our stratified analysis, people in urban areas were more likely to benefit from greenness, and people in rural areas were more likely to be harmed by air pollution. There was no effect modification by sex. InterpretationOur study showed that there is a synergistic effect of greenness and air pollution, which has important implications for urban planning and air pollution control to improve public health. FundingNone.