Associations between particulate matter air pollution, presence and progression of subclinical coronary and carotid atherosclerosis: A systematic review

Background and aims: Long-term exposure to particulate matter (PM) air pollution has been linked with increased cardiovascular events and mortality, however, studies had shown inconsistent associations between PM exposure and subclinical atherosclerosis. Methods: We performed an updated systematic literature review to identify studies evaluating the associations between PM and subclinical atherosclerosis, measured using presence/progression of coronary artery calcium (CAC) or carotid intima-media thickness (CIMT) in adult populations. Quality was assessed using the Newcastle-Ottawa scale. Results: Eighteen studies were included: 5 cohorts and 13 cross-sectional. Amongst 7 studies that evaluated the associations between PM and prevalence of CAC, 4 reported significantly higher odds of detectable CAC>0 or CAC>400 with increased PM exposure. Nine studies evaluated the association between exposure to at least one of the particulates and CIMT; of these, 6 reported significant independent associations. Two studies evaluated PM_2.5 and CAC progression, with 1 reporting a greater progression of CAC with increased exposure to PM, while 3 out of 4 studies evaluating CIMT progression showed no significant difference in CIMT progression with a higher PM_2.5 exposure. Additionally, 3 studies found significant associations between proximity to major roadways and measures of subclinical atherosclerosis. Among null studies, most displayed non-significant trends towards higher atherosclerosis burden with higher PM exposure. Conclusions: Overall, available observational studies support a positive association between PM exposure and subclinical atherosclerosis. Further longitudinal studies are needed to better establish this relationship and assess the efficacy of previously identified interventions on mitigation of clinical cardiovascular disease.