Joint associations of PM10 and smoking with the risk of new-onset stroke in middle-aged and older adult Chinese adults: findings from the CHARLS cohort study

Abstract

Background: The relationship between long-term exposure to particulate matter ≤ 10 μm in diameter (PM₁₀), 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 PM₁₀ 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/m³ increase in PM₁₀ concentration was associated with a 0.3% higher risk of stroke (HR = 1.003; 95% CI: 1.000-1.005; p = 0.04). A nonlinear exposure-response relationship was observed (P for non-linearity = 0.04). Among PM₁₀ exposure quartiles, only the third quartile (91.90-115.92 μg/m³) was significantly associated with increased stroke risk (HR = 1.36; 95% CI: 1.08-1.71; p < 0.01). Participants exposed to both high PM₁₀ levels (≥91.9 μg/m³) and smoking had the highest stroke risk (HR = 1.72; 95% CI: 1.33-2.23; p < 0.01). No significant multiplicative or additive interaction between PM₁₀ and smoking was found.

Conclusion: Long-term PM₁₀ exposure and smoking are independent risk factors for stroke. The elevated risk observed within a specific concentration range of PM₁₀ 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.

Keywords: cigarette smoking; cohort study; environmental exposure; particulate matter 10; stroke risk.

Figure 1

Flowchart of study inclusion and exclusion criteria. CHARLS, China Health and Retirement Longitudinal Study; CHAP, China High Air Pollution; PM₁₀, particulate matter ≤ 10 μm in diameter; BMI, body mass index; SBP, systolic blood pressure; DBP, diastolic blood pressure.

Figure 2

Nonlinear association between PM₁₀ exposure and stroke risk. The restricted cubic spline curve shows the adjusted hazard ratio (HR) of stroke across PM₁₀ concentrations. The model adjusted for age, gender, education, marital status, residence, smoking, drinking, dyslipidemia, heart conditions, hypertension, diabetes, body mass index, systolic blood pressure, and diastolic blood pressure. The dashed horizontal line indicates the reference (HR = 1.0). p-values test the nonlinearity (p = 0.04) and overall association (p < 0.01). Shaded regions represent 95% confidence intervals. PM₁₀, particulate matter ≤ 10 μm in diameter.

Figure 3

Hazard ratios (HRs) of stroke risk by PM₁₀ exposure and smoking status. Adjusted hazard ratios (dots) and 95% confidence intervals (bars) show stroke risk across combined categories of PM₁₀ exposure (stratified at 91.9 μg/m³) and smoking status. The model was adjusted for age, gender, education, marital status, residence, drinking, dyslipidemia, heart conditions, hypertension, diabetes, body mass index, systolic blood pressure, and diastolic blood pressure. PM₁₀, particulate matter ≤ 10 μm in diameter.

Figure 4

Subgroup analysis of stroke risk by combined PM₁₀ exposure and smoking status, stratified by age, gender, and education level Forest plot showing hazard ratios (HRs) and 95% confidence intervals (CIs) for stroke risk in subgroups defined by combined PM₁₀ exposure (cutoff: 91.9 μg/m³) and smoking status. Analyses are stratified by age (<60 vs. ≥60 years), gender, and education level. Reference group (Ref): non-smokers with PM₁₀ exposure below 91.9 μg/m³. PM₁₀, Particulate Matter ≤ 10 μm in diameter; HR, Hazard Ratio.