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

Background: Racial/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. Objective: To assess the potential mediating effects of ambient air pollution on the association between race/ethnicity and blood pressure levels. Methods: We 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 (PM_2.5), oxides of nitrogen (NO_X), and ozone (O₃) for the year 2000 were estimated for participants. Results: The difference in SBP levels by race/ethnicity that was related to higher PM_2.5 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. PM_2.5 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 NO_X. Conclusion: Racial disparities in blood pressure were reduced after accounting for PM_2.5 and ozone while increased after accounting for NO_X.