Long-term exposure to NO₂ and ozone and hypertension incidence in the black women's health study

BACKGROUND Evidence shows that exposure to air pollutants can increase blood pressure in the short and long term. Some studies show higher levels of hypertension prevalence in areas of high pollution. Few data exist on the association of air pollution with hypertension incidence. The purpose of the present study was to prospectively assess the associations of the trafc-related nitrogen dioxide (NO₂) and of ozone with the incidence of hypertension in the Black Women's Health Study (BWHS), a large cohort study of African American women. METHODS We used Cox proportional hazards models to calculate hazard ratios (HRs) and 95% confdence intervals (CI) for hypertension associated with exposure to NO₂ and ozone among 33,771 BWHS participants. NO₂ and ozone levels at participant residential locations were estimated with validated models. RESULTS From 1995 to 2011, 9,570 incident cases of hypertension occurred in a total of 348,154 person-years (median follow-up time, 11 years). The multivariable HRs per interquartile range of NO₂ (9.7 ppb) and ozone (6.7 ppb) were 0.92 (95% CI = 0.86, 0.98) and 1.09 (95% CI = 1.00, 1.18). CONCLUSIONS In this large cohort of African American women, higher ozone levels were associated with an increase in hypertension incidence. Higher NO₂ levels were not associated with greater hypertension incidence; indeed, incidence was lower at higher NO₂ levels.