Joint associations of PM and smoking with the risk of new-onset stroke in middle-aged and older adult Chinese adults: findings from the CHARLS cohort study.

Background: The relationship between long-term exposure to particulate matter ≤ 10 μm in diameter (PM), smoking, and stroke risk remains unclear. This study investigates their association.

Methods: We analyzed data from 10,839 participants in the 2013 wave of the China Health and Retirement Longitudinal Study (CHARLS). Long-term PM exposure was estimated using the China High Air Pollution (CHAP) dataset, and incident stroke cases were self-reported during follow-up through 2018. Multivariable Cox proportional hazards models, restricted cubic spline (RCS) analyses, and joint exposure models were employed.

Results: Each 1 μg/m increase in PM concentration was associated with a 0.3% higher risk of stroke (HR = 1.003; 95% CI: 1.000-1.005;  = 0.04). A nonlinear exposure-response relationship was observed (P for non-linearity = 0.04). Among PM exposure quartiles, only the third quartile (91.90-115.92 μg/m) was significantly associated with increased stroke risk (HR = 1.36; 95% CI: 1.08-1.71;  < 0.01). Participants exposed to both high PM levels (≥91.9 μg/m) and smoking had the highest stroke risk (HR = 1.72; 95% CI: 1.33-2.23;  < 0.01). No significant multiplicative or additive interaction between PM and smoking was found.

Conclusion: Long-term PM exposure and smoking are independent risk factors for stroke. The elevated risk observed within a specific concentration range of PM suggests a potential threshold or saturation effect. Individuals exposed to both risk factors are particularly vulnerable, highlighting the need for integrated public health strategies targeting both air quality improvement and smoking cessation.