The association of particulate matter 2.5 exposure with frailty trajectories in middle-aged and older Chinese adults and the potential modification by lifestyle and socioeconomic status

OBJECTIVE: To examine PM2.5 exposure associations with frailty trajectories in middle-aged and older Chinese adults, and evaluate modifying effects of lifestyle and socioeconomic status (SES). METHODS: We analyzed 10,659 participants from CHARLS using PM2.5 data from Dalhousie University. Frailty was assessed via a deficit accumulation index. Group-based trajectory modelling (GBTM) identified frailty trajectories; ordered logistic regression estimated associations and effect modifications. RESULTS: Three trajectories emerged: "Stable low" (63.95%), "Increased to frailty" (29.00%), and "Continuously worsening" (7.05%). Each 10 μg/m³ PM2.5 increase raised odds of Trajectories 2 and 3 by 15.2% and 12.3%, respectively. Higher SES attenuated PM2.5 effects (RERI=-0.067), while unhealthy sleep duration amplified them (RERI=0.163). CONCLUSIONS: PM2.5 exposure is associated with deteriorating frailty trajectories. Higher SES exerts an antagonistic effect, whereas unhealthy sleep duration has a synergistic effect on PM2.5-related frailty progression.