Ambient air pollution as a mediator in the pathway linking race/ethnicity to blood pressure elevation: The multi-ethnic study of atherosclerosis (MESA)

Abstract

BackgroundRacial/ethnic disparities in blood pressure and hypertension have been evident in previous studies, as were associations between race/ethnicity with ambient air pollution and those between air pollution with hypertension. The role of air pollution exposure to racial/ethnic differences in hypertension has not been explored. ObjectiveTo assess the potential mediating effects of ambient air pollution on the association between race/ethnicity and blood pressure levels. MethodsWe studied 6,463 White, Black, Hispanic and Chinese adults enrolled across 6 US cities. Systolic (SBP) and diastolic blood pressure (DBP) were measured at Exam 1 (2000–2002) and Exam 2 (2002–2004). Household-level annual average concentrations of fine particulate matter (PM2.5), oxides of nitrogen (NOX), and ozone (O3) for the year 2000 were estimated for participants. ResultsThe difference in SBP levels by race/ethnicity that was related to higher PM2.5 concentrations compared with White men (“indirect associations”) was 0.3 (95% CI: 0.1, 0.6) mmHg for Black men, 0.3 (95% CI: 0.1, 0.6) mmHg for Hispanic men and 1.0 (95% CI: 0.2, 1.8) mmHg for Chinese men. Findings were similar although not statistically significant for women. PM2.5 did not mediate racial/ethnic differences in DBP. Indirect associations were significant for O3 for SBP among women and men and for DBP among men. In contrast, racial/ethnic disparities were attenuated due to exposure to NOX. ConclusionRacial disparities in blood pressure were reduced after accounting for PM2.5 and ozone while increased after accounting for NOX.