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

Background: Exposure to fine particulate matter (PM) has been linked to an increased risk of atherosclerosis. However, it remains unclear whether specific compounds within PM, 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 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 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 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/m] 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 compound as a mixture (posterior inclusion probability [PIP]: 1.00).

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