Associations Between PM_2.5 Components and Cardiovascular Diseases: A Cohort Study of 0.5 Million Chinese Adults

Evidence linking components of particulate matter with diameters ≤2.5 μm (PM_2.5) to the incidence of cardiovascular disease (CVD) remains scarce and inconsistent.

The aim of this study was to investigate the associations of long-term exposure to PM_2.5 components with incident CVD risk, considering both absolute concentrations and relative proportions.

This study included 487,037 participants from the China Kadoorie Biobank who were free of CVD or cancer at baseline. Three-year moving average concentrations of PM_2.5 and its components (black carbon [BC], organic matter, chloride [Cl^-], nitrate [NO₃^-], sulfate [SO₄^2-], and ammonium [NH₄⁺]) were geocoded to participants at 1 × 1 km resolution according to their community recruitment clinic locations. Time-varying Cox proportional hazards models were used to evaluate the associations between PM_2.5 components and incident CVD risk. Substitution models were used to estimate the effects of reallocating PM_2.5 component proportions while keeping total PM_2.5 mass constant, thereby evaluating changes in CVD risk associated with shifts in component composition.

Over a median 15.1-year follow-up, a total of 196,224 CVD cases, including 72,747 of ischemic heart disease, 74,594 of ischemic stroke, 17,553 of hemorrhagic stroke, and 54,306 of other cerebrovascular diseases, were documented. Long-term exposure to PM_2.5 components was associated with increased risk for CVD and its major subtypes. For total CVD, the HRs per IQR increase were 1.15 (95% CI: 1.13-1.17) for BC, 1.17 (95% CI: 1.15-1.18) for organic matter, 1.28 (95% CI: 1.25-1.32) for Cl^-, 1.29 (95% CI: 1.24-1.33) for NO₃^-, and 1.23 (95% CI: 1.20-1.25) for SO₄^2-. Higher proportions of Cl^-, SO₄^2-, and BC were associated with an increased risk for ischemic stroke, and the aforementioned inorganic ions were also positively associated with ischemic heart disease. Substituting 1% of any other PM_2.5 component with Cl^- was associated with a 3% to 8% higher risk for total CVD, whereas substitutions with BC were associated with a 1% to 8% higher risk for ischemic stroke, and substitution with SO₄^2- was associated with a 2% to 5% higher risk for ischemic heart disease.

Long-term exposure to PM_2.5 chemical components was positively associated with CVD risk. Critically, CVD risk was influence by compositional shifts, with a particularly hazardous profile characterized by higher proportions of Cl^-, BC, or SO₄^2-. These findings underscore the importance of implementing targeted, health-oriented control strategies that prioritize specific PM_2.5 components.