Interaction between walkability and fine particulate matter on ischemic heart disease: A prospective cohort study in...

Previous studies have suggested that neighborhoods characterized by higher walkability are related to a reduced risk of ischemic heart disease (IHD), whereas exposure to PM_2.5 is positively associated with risk of IHD. Nevertheless, their joint impact on IHD warrants further investigation.

This prospective cohort study was performed in Yinzhou, Ningbo, China, comprising 47,516 participants. Individual-level walkability and PM_2.5 were evaluated using a commercial walkability database and a land use regression (LUR) model, respectively. Hazard ratios (HRs) and 95 % confidence intervals (95 % CIs) were calculated using two Cox proportional hazards models: one based on two-year average PM_2.5 levels prior to baseline, and the other incorporating time-varying PM_2.5 assessed on a monthly scale. Dose-response relationships were explored using restricted cubic spline (RCS) functions. Interactions on both additive and multiplicative scales were assessed via relative excess risk due to interaction (RERI) and likelihood-ratio tests. Joint effects were explored and visualized using a 3D wireframe plot.

Over a median follow-up of 5.14 years, 1735 incident cases of IHD were identified. Adjusted HRs (95 % CIs) were 1.56 (1.34-1.81) per 10 μg/m³ increase in PM_2.5 and 0.96 (0.94-0.98) per 10-unit increase in walkability, with both exposures exhibiting non-linear dose-response relationships. Walkability and PM_2.5 were positively correlated (r_s = 0.12, P < 0.001), and a multiplicative interaction was detected (P_interaction = 0.019).

Walkability was inversely associated with risk of IHD, whereas exposure to PM_2.5 was positively associated with IHD. Notably, the pernicious effects of PM_2.5 could be attenuated in areas with higher levels of walkability. Our findings underscore the significance of walkable urban design, air quality improvement, as preventive strategies for IHD.