Residential greenness, air pollution and visual impairment: a prospective cohort study

The aim of this study was to investigate the associations between residential greenness, air pollution (PM2.5, PM10, and NO2), and the risk of visual impairment in Chinese middle-aged and elderly adults. The data were used from the China Health and Retirement Longitudinal Study (CHARLS), focusing on adults aged 45 years and older. Exposure to residential greenness was assessed using the Normalized Difference Vegetation Index (NDVI), while air pollution exposure (PM2.5, PM10, and NO2) was estimated from the ChinaHighAirPollutants dataset. Visual impairment was self-reported and categorized as distance visual impairment (DVI) and near visual impairment (NVI). Cox proportional hazards models were applied to investigate the associations between residential greenness, air pollution, and visual impairment. Furthermore, we investigated the potential modification and mediation relationship between residential greenness, air pollution and visual impairment. A total of 9,591 participants were included in this study. During a 7-year period, 2,650 cases of DVI and 3,130 cases of NVI were identified. In the single exposure model, a higher level of residential greenness was associated with a significantly reduced risk of both DVI and NVI. Specifically, for every 0.1 unit increase in NDVI, the hazard ratio (HR) was 0.68 (95%CI: 0.65,0.71) for DVI, and 0.67 (95%CI: 0.64,0.69) for NVI. Conversely, exposure to air pollution was positively associated with increased risks for both DVI and NVI. For each 10 µg/m3 increase in PM2.5, the HR was 1.60 (95%CI: 1.56,1.65) for DVI and 1.64 (95%CI: 1.60,1.69) for NVI. Similarly, PM10 and NO2 exposure showed elevated risks with HR of 1.28 (95%CI: 1.27,1.30) and 1.73 (95%CI: 1.62,1.85) for DVI, and 1.30 (95%CI: 1.28,1.32) and 1.82 (95%CI: 1.72,1.94) for NVI, respectively. The multiple exposure model also showed significant association between residential greenness, air pollution and visual impairment risk. Additionally, the adverse effects of PM2.5, PM10, and NO2 were attenuated in areas with the highest levels of residential greenness. Mediation analysis revealed that air pollution mediated a significant portion of the association between residential greenness and visual impairment. This study suggests that increased residential greenness may reduce the risk of visual impairment, partially by mitigating air pollution exposure. These findings highlight the environmental benefits to improve air quality and enhance green spaces, thereby promoting visual health in aging populations.