Association of fine particulate matter and residential green space with rheumatoid arthritis

Fine particulate matter (PM_2.5) is a recognized risk factor for respiratory and cardiovascular diseases, but the association between PM_2.5 and rheumatoid arthritis (RA) is still controversial. Additionally, evidence on the relationship of green space with RA is scarce. This study aimed to investigate the separate and combined associations of PM_2.5 and green space with risk of RA.

Our study involved 30,684 participants from the Yinzhou cohort in Ningbo, China. PM_2.5 concentrations were determined using a land-use regression model. Residential green space was assessed using the Normalized Difference Vegetation Index (NDVI) and Enhanced Vegetation Index (EVI) from satellite images. We employed the Cox proportional hazard model to evaluate the relationships of PM_2.5 and green space with RA.

During the 176,894 person-years of follow-up period, 354 cases of RA were identified. Hazard ratio (HR) and the corresponding 95% confidence interval (95% CI) for every interquartile range (IQR) increase in PM_2.5 were 1.23 (95% CI: 1.02, 1.49). Compared with lower exposure to residential green space, individuals living in areas with more green space had a decreased risk of RA (HR was 0.80 (95% CI: 0.70, 0.92), 0.80 (95% CI: 0.70, 0.92), and 0.79 (95% CI: 0.70, 0.89) for 250m, 500m, and 1000m NDVI buffers, respectively). Similar results were observed for the association between EVI and RA. Furthermore, a significant multiplicative interaction was observed between PM_2.5 and green space (NDVI 250m and EVI 250m). No mediating effect of PM_2.5 on the relationship between green space and RA was observed.

Our findings indicated that living in areas with higher green space was linked to a reduced risk of RA, whereas living in areas with higher PM_2.5 was associated with an increased risk of RA. The beneficial effect of high green space may be offset by exposure to PM_2.5.