Associations of exposure to PM2.5 and its compounds with carotid intima-media thickness among middle-aged adults.

Background: Exposure to fine particulate matter (PM_2.5) has been linked to an increased risk of atherosclerosis. However, it remains unclear whether specific compounds within PM_2.5, rather than the overall mass, serve as a better indicator of adverse cardiovascular health outcomes associated with air pollution.

Methods: In this cross-sectional study, we included 3257 participants (aged 37-51 years) from the Coronary Artery Risk Development in Young Adults (CARDIA) study. Exposure to PM_2.5 and its constituent compounds, black carbon (BC), ammonium, nitrate, organic matter, sulfate, mineral dust, and sea salt were included in the analyses. Carotid intima media thickness (cIMT; the average of common, bulb, and internal carotid) was measured by carotid ultrasonography. We assessed the cross-sectional associations of one-year exposure to PM_2.5 and its compounds with mean cIMT using linear regression models adjusting for participants' demographics, individual- and neighborhood-level socioeconomic status, behavioral components, and health conditions. We also adopted Bayesian kernel machine regression (BKMR) models to investigate the association between the PM_2.5 compound mixture and cIMT as well as the contribution of each compound to the association.

Results: Greater exposure to BC was associated with higher cIMT (mm) (β =0.034, 95 % CI = 0.019-0.049, per IQR increase [0.56 μg/m³] of BC) among participants with a mean age of 45.0, consisting of 45.9 % Black and 54.1 % White males and females. The association was generally consistent across participants' demographic characteristics. In our BKMR analysis, BC exhibited a dose-response association with cIMT with a high contribution to the association of cIMT with PM_2.5 compound as a mixture (posterior inclusion probability [PIP]: 1.00).

Conclusions: Our findings suggest that certain compounds of PM_2.5, such as BC, may offer more reliable indications of the impact of air pollution on cardiovascular health.