Interaction Between Residential Greenness and Air Pollution Mortality: Analysis of the Chinese Longitudinal Healthy Longevity Survey (CLHLS)

Backgrounds: Both air pollution and green space have been shown to affect health. We aim to assess whether greenness protects against air pollution-related mortality. Methods: We used 2008 wave of the Chinese Longitudinal Healthy Longevity Survey. We calculated contemporaneous Normalized Difference Vegetation Index (NDVI) in the 500m radius around the residence. 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: We followed up 12,873 participants totaling 47,884 person-years. There were 7,426 mortality events from 2008 to 2014. The mean contemporaneous and 3-year average PM2.5 were 0⋅42 (SD: 0⋅21), and 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 (95% CI: 1⋅09, 1⋅18), and the interaction term was 1⋅01 (95% CI: 1⋅00, 1⋅02) with a statistical significance (p-value: 0⋅027). In the stratified analysis, we found people in urban areas are more likely to benefit from greenness, and people in rural areas are more likely to be harmed by air pollution. Interpretation: Our study showed some indication of a synergistic effect of greenness and air pollution, which implies that urban green space planning and air pollution control can jointly improve public health. Funding Statement: This study was supported by Bill & Melinda Gates Foundation (Grant Number: OOP1148464), the United States National Institute of Health (Grant Number: 2P01AG031719), National Key R&D Program of China (Grant Number: 2018YFC2000400), and National Natural Science Foundation of China (Grant Number: 71490732). Declaration of Interests: JSJ served as the Asia Editor of The Lancet in 2017. The other authors declare no competing interests. Ethics Approval Statement: The CLHLS study was approved by the Institutional Review Board, Duke University (Pro00062871), and the Biomedical Ethics Committee, Peking University (IRB00001052-13074). All participants signed a written informed consent.