Joint associations of air pollution and residential greenness with chronic disease in a longitudinal Chinese cohort

Long–term exposure to fine particulate matter (PM 2.5 ) and residential greenness are often correlated but commonly evaluated separately. We examined the joint nonlinear associations with chronic disease outcomes and estimated potential health gains under counterfactual scenarios among middle-aged and older adults in China. We analyzed 33,712 participant-wave observations from the China Family Panel Studies (CFPS; 2010–2022). Chronic disease status was based on self-reported physician-diagnosed conditions. County/district-level PM 2.5 and Normalized Difference Vegetation Index (NDVI) exposures were assigned using 10-year lagged averages. Generalized additive mixed models with participant-specific random intercepts and survey-wave fixed effects estimated single- and joint-exposure response functions, followed by health impact assessment (HIA). In fully adjusted single-exposure models, both PM 2.5 and NDVI smooth terms remained significant (effective degrees of freedom [EDF] = 2.69 and 3.00, respectively; p < 0.001). The joint PM 2.5 –NDVI interaction was also significant (EDF = 6.70, p < 0.001), indicating that estimated disease risk varied across combined exposure profiles. HIA estimates were scenario-dependent; the more intensive joint-improvement scenario produced the largest model-estimated burden reduction, with a joint population attributable fraction of 4.75% (95% CI: 4.65–4.84). The findings support considering correlated environmental exposures when evaluating coordinated air-quality and greenness strategies.