Residential greenness, air pollution, and incident ischemic heart disease: A prospective cohort study in China

Greener residential surroundings are associated with beneficial health outcomes, whereas higher air pollution exposure is linked with elevated risks of chronic diseases. To date, limited studies have explored the interaction between residential greenness and air pollution on the risk of ischemic heart disease (IHD). We performed a prospective cohort study that included 29,141 adult participants recruited from Yinzhou District, Ningbo, China. Normalized Difference Vegetation Index (NDVI) around each participant's residence was calculated to measure residential greenness exposure. Land-use regression models were conducted to estimate long-term individual exposure to air pollutants, including nitrogen dioxide (NO2) and particulate matter with aerodynamic diameters ≤ 2.5 μm (PM2.5) and ≤10 μm (PM10). Cox proportional hazard models were used to calculate the hazard ratios (HRs) and 95% confidence intervals (95% CIs) for the associations of residential greenness and air pollutants with the risk of incident IHD. During 101,172.5 person-years of follow-up, 1392 incident IHD cases were reported in the study population. Residential greenness, expressed as an interquartile range (IQR) increase in NDVI within 250 m, was inversely associated with incident IHD (HR = 0.89, 95%CI: 0.81,0.98). However, long-term exposures to air pollution were associated with higher IHD incidence (HR = 1.21, 95%CI:1.10,1.33 per IQR increase for PM2.5; HR = 1.12, 95%CI:1.03,1.22 per IQR increase for PM10; HR = 1.09, 95%CI:1.02,1.16 per IQR increase for NO2). Mediation analyses suggested that the beneficial effect of residential greenness on incident IHD could be partly mediated by reducing the exposure to PM2.5. These findings suggested that higher greenness was associated with decreased risk of IHD, while air pollutants were positively associated with incident IHD. Meanwhile, residential greenness may decrease the risk of IHD by reducing exposure to PM2.5.