Association between cumulative social risk, particulate matter environmental pollutant exposure, and cardiovascular disease risk.

Background: Long-term exposure to pollution has been shown to increase risk of cardiovascular disease (CVD) and mortality, and may contribute to the increased risk of CVD among individuals with higher social risk.
Methods: Data from the community-based Heart Strategies Concentrating on Risk Evaluation (HeartSCORE) study were used to quantify Cumulative Social Risk (CSR) by assigning a score of 1 for the presence of each of 4 social risk factors: racial minority, single living, low income, and low educational status. 1-year average air pollution exposure to PM _2.5 was estimated using land-use regression models. Associations with clinical outcomes were assessed using Cox models, adjusting for traditional CVD risk factors. The primary clinical outcome was combined all-cause mortality and nonfatal CVD events.
Results: Data were available on 1933 participants (mean age 59 years, 66% female, 44% Black). In a median follow up time of 8.3 years, 137 primary clinical outcome events occurred. PM _2.5 exposure increased with higher CSR score. PM _2.5 was independently associated with clinical outcome (adjusted hazard ratio [HR]: 1.19 [95% CI: 1.00, 1.41]). Participants with ≥2 CSR factors had an adjusted HR of 2.34 (1.48-3.68) compared to those with CSR = 0. The association was attenuated after accounting for PM _2.5 (HR: 2.16; [1.34, 3.49]). Mediation analyses indicate that PM _2.5 explained 13% of the risk of clinical outcome in individuals with CSR score ≥ 2.
Conclusion: In a community-based cohort study, we found that the association of increasing CSR with higher CVD and mortality risks is partially accounted for by exposure to PM _2.5 environmental pollutants.