Association between City-Level Particulate Matter Exposure and Frailty among Middle-Aged and Older Adults in China

Introduction: The effects of exposure to particulate matter and frailty, as well as its exposure-response relationship, have not been effectively explored. This study aimed to explore the association between long-term exposure to particulate matter and frailty state and each dimension in Chinese middle-aged and older adults, in addition to the exposure-response relationship. Methods: The data were obtained from the National Urban Air Quality Real-Time Dissemination Platform and China Health and Retirement Longitudinal Study (CHARLS). Frailty was measured by a frailty index containing 39 indicators. Annual averages of seven pollutants were calculated from hourly monitoring data. We used multilevel regression modeling to explore the association between long-term exposure to particulate matter and frailty. Meanwhile, we explored the exposure-response relationship based on a multilevel generalized summation model. We performed a sensitivity analysis using a multi-pollution model and a quantile-based g-computation (QGC) model. Results: A total of 15,611 participants were included in the analysis. We find that long-term exposure to PM_2.5 was associated with an increased risk of pre-frailty and frailty (all p < 0.05). PM_c and PM₁₀ exhibited similar associations. The exposure-response relationship between PM_2.5 showed a linear relationship, whereas the exposure-response relationship between PM₁₀, PM_c showed a nonlinear relationship. Elevated PM_2.5 concentrations showed significant positive associations with the number of chronic disease score, IADL score, and functional limitation status score (all p < 0.05). PM₁₀ and PM_c showed similar positive correlations. These results remained robust after sensitivity analyses using a multi-pollution model and QGC model. Conclusion: Chronic exposure to particulate matter was significantly associated with increased risk of frailty. The exposure-response relationship between PM_2.5 concentration and frailty showed a linear relationship, and the exposure-response relationship between PM₁₀ and PM_c showed a nonlinear relationship. Exposure to a mixture of pollutants carried a higher risk of frailty than exposure to a single pollutant.