Abstract
While ambient fine particulate matter (PM(2.5)) and ozone (O(3)) are extensively associated with population health, no studies have yet assessed the potential association between concurrent exposure to these two pollutants and physical function (PF) in middle-aged and elderly individuals. By collecting data from three phases of the China Health and Retirement Longitudinal Study (CHARLS), we included 8834 follow-up observations from 4110 participants aged 45 years and older who had undergone at least two physical examinations between 2011 and 2015. PF scores of enrolled participants were assessed through four objective tests including grip strength, balance, walking speed, and repeated chair stands. Annual average concentrations of PM(2.5) and O(3) prior to physical tests were assigned to participants at the prefecture-level residence in each survey. A linear mixed-effects model was used to evaluate the effects of long-term exposure to PM(2.5) and O(3) on PF, adjusting for multiple covariates including sociodemographic, behavioral, and health status. Stratified analyses were performed to compare the effects of PM(2.5) under low- and high-level O(3) groups and the effects of O(3) under low- and high-level PM(2.5) groups. Additive interactive effects were testified by introducing a 2 × 2-level dummy variable to model the joint exposure of PM(2.5) and O(3). Each 10-µg/m³ increase in PM(2.5) and O(3) exposure was associated with a declined PF score of -0.561 points (95% confidence interval: -0.617, -0.506) and -1.154 points (-1.341, -0.968), respectively. Stratified analyses for co-pollutants indicated weakened effects of PM(2.5) and O(3) at higher co-pollutant levels (PM(2.5): -0.448 [-0.522, -0.373]; O(3): -0.796 [-1.070, -0.522]) than at lower levels (PM(2.5): -0.608 [-0.708, -0.507]; O(3): -1.293 [-1.612, -0.974]). Despite greater effects in the case of simultaneous high-level exposures to both pollutants, we did not identify any evidence for additive interactive effects of co-exposures to PM(2.5) and O(3) in the total and age- and sex-subgroup populations. This study provided novel evidence for the independent and modifying effects of long-term exposure to PM(2.5) and O(3) on impaired PF in middle-aged and elderly people.