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

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 (PM(2·5)) 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, PM(2·5), 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 PM(2·5) was 49·63 μg/m(3) (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/m(3) increase in PM(2·5) 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.