Ozone Levels Linked to Hypertension Rates.

Black women who live in neighborhoods with higher levels of ozone are more likely to be diagnosed with hypertension compared to women who live in neighborhoods with lower ozone levels, according to a new study led by School of Public Health researchers affiliated with the Slone Epidemiology Center.

The study, in the American Journal of Hypertension, found that for every 6.7 ppb (parts per billion) increase in ozone levels, there was a 9 percent increase in hypertension incidence.  In contrast, higher levels of traffic-related nitrogen oxides (NO₂) did not increase the risk of hypertension.

The analysis was based on more than 33,000 women in 56 major US cities—participants in BU’s long-running Black Women’s Health Study who have been providing information on their health, including diagnoses of hypertension and other conditions, since 1995. 

The study estimated levels of pollutants using validated models.  More than 9,500 of the 33,771 study participants, or 28 percent, reported incident hypertension during the study period, 1995 to 2011. The researchers controlled for a number of confounding factors, including weight, smoking, and socioeconomic status.

“The hypothesis that exposure to air pollutants could increase the risk for hypertension is biologically plausible, although most evidence pertains to PM2.5 (particulate matter), rather than gaseous pollutants,” the authors said. They said substantial evidence exists supporting the idea that PM2.5 inhalation is capable of increasing blood pressure over both the short term (a few days) and long term (one year).

Lead author Patricia Coogan, senior epidemiologist at Slone and a research professor of epidemiology, said the study raises a new question that requires further research and confirmation.

“While we expected that NO2 would increase the risk of hypertension because it is a surrogate for particulate-bearing traffic pollution, the finding of a positive association of ozone levels with hypertension risk was unexpected,” she said. “This finding needs confirmation in other studies.” 

The authors noted that positive associations between pollution and hypertension are of particular concern for African American women, who have higher rates of hypertension and cardiovascular disease than whites. In addition, due to the legacy of racial segregation in housing, it is well documented that predominately black and poor neighborhoods have, on average, higher levels of air pollution than predominately white neighborhoods.

BU study co-authors include: Laura White; associate professor of biostatistics; Traci Bethea, an epidemiologist at Slone and assistant professor of medicine at the School of Medicine; Lynn Rosenberg, principal investigator of the Black Women’s Health Study and professor of epidemiology; and Jeffrey Yu of Slone.

Other authors were from the University of Michigan Medical School, Health Canada, the University of Washington, and the University of California, Los Angeles.

—Lisa Chedekel