Interaction between residential greenness and air pollution mortality: analysis of the Chinese Longitudinal Healthy Longevity Survey.

Summary Background Both air pollution and green space have been shown to affect health. We aimed to assess whether greenness protects against air pollution-related mortality. Methods We used data from the 2008 wave of the Chinese Longitudinal Healthy Longevity Survey. We calculated contemporaneous normalised difference vegetation index (NDVI) in the 500 m radius around each participant's residence. Fine particulate matter (PM2·5) concentration was calculated using 3-year average concentrations in 1 km × 1 km grid resolution. We used Cox proportional hazards models to estimate the effects of NDVI, PM2·5, and their interaction on all-cause mortality, adjusted for a range of covariates. Findings The cohort contained 12 873 participants, totalling 47 884 person-years. There were 7426 deaths between 2008 and 2014. The mean contemporaneous NDVI was 0·42 (SD 0·21), and the mean 3-year average PM2·5 was 49·63 μg/m3 (13·72). In the fully adjusted model, the mortality hazard ratio 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), and the interaction term was 1·01 (1·00–1·02) with a p value of 0·027. We observed non-linear associations in our stratified analyses: people living in urban areas were more likely to benefit from greenness, and people living in rural areas were more likely to be harmed by air pollution. Interpretation Our study showed some indication of a synergistic effect of greenness and air pollution, suggesting that green space planning and air pollution control can jointly improve public health. Funding Bill & Melinda Gates Foundation, National Institutes of Health, National Key R&D Program of China, National Natural Science Foundation of China.