Long-term exposure to fine particulate constituents and cardiovascular diseases in Chinese adults

Background: Ambient fine particulate matter (PM_2.5) has been linked to various cardiovascular disease (CVD) endpoints. However, little is known regarding the health effects of PM_2.5 constituents. This study aimed to assess the associations of CVD incidence with long-term exposures to PM_2.5 constituents in China, including black carbon (BC), organic matter (OM), sulfate (SO₄^2-), nitrate (NO₃^-) and ammonium (NH₄⁺).

Methods: A nationwide cohort of 14,331 adults were drawn from the China Family Panel Study, a high-quality longitudinal survey initiated from 2010 over 25 provincial regions in China. We used the baseline survey and the ensuing three waves of follow-up data during 2010-2017 to conceive our study cohort. Annual county-level exposures of PM_2.5 and its constituents for each participant were assessed by aggregating satellite-derived estimates at a monthly time-scale and 1 km-resolution. A directed acyclic graph (DAG) was developed to identify confounding variables. Cox proportional hazards models with time-varying exposures and province-level random intercepts were employed to quantify associations of CVD incidence with long-term exposures to PM_2.5 and its constituents.

Results: During 84,162.4 person-years' follow-up, a total of 1575 CVD, 953 hypertension and 342 stroke incidents occurred. DAG-based Cox model estimated an hazard ratio (HR) of 1.291 (95% confidence interval: 1.147-1.454) for total CVD and 1.326 (1.151-1.528) for hypertension, associated with per interquartile range (IQR=27.9 μg/m³) increase in exposure to PM_2.5 mass. Elevated CVD risks were also significantly related to several PM_2.5 constituents, with the largest HRs observed in SO₄^2- (1.721 [1.517-1.951], IQR = 5.67 μg/m³), followed by NH₄⁺ (1.537 [1.341-1.762], IQR = 4.44 μg/m³), NO₃^- (1.311 [1.128-1.523], IQR = 8.92 μg/m³) and BC (1.294 [1.158-1.446], IQR = 2.28 μg/m³). No associations were identified between long-term exposures to particulate constituents and incidence of stroke. Associations with PM_2.5 and constituents (BC, NO₃^-, NH₄⁺ and SO₄^2-) were more pronounced among adults aged over 50 years, and residents in southern region.

Conclusions: Long-term exposures to PM_2.5 mass and specific constituents (i.e., BC, NO₃^-, NH₄⁺ and SO₄^2-) were associated with increased risks of total CVD and hypertension incidence in Chinese adults. Findings may have implications for in-depth understandings of biological mechanisms in chronic impacts of ambient PM_2.5 on cardiovascular health.