Postmenopausal women who live close to major roadways may suffer from high blood pressure more than do women in less-trafficked areas, according to the findings of a new study that included University faculty and a Brown graduate student among its many authors.
The study was published Oct. 1 in the Journal of the American Heart Association.
“We found that women that lived within 100 meters of a major roadway were 23 percent more likely to have hypertension, compared to women who lived more than a kilometer away,” said Gregory Wellenius, an associate professor of epidemiology and one of the authors of the study.
“There’s been conflicting results in the past regarding the built environment and cardiovascular health, (but) there’s been few studies that have specifically looked at distance to roadway and risk of hypertension,” he said.
The paper’s lead author, Kipruto Kirwa GS, added that this study was done in order to address this “gap in the literature.” Not many scientific studies have examined something “as simple as how far from a major road you reside,” he said. Kirwa said his work was motivated in part by his background as a Kenyan and his interest in examining “pollution and its effects on health both here and in developing countries.”
To conduct their analyses, researchers used data that had already been collected by the Women’s Health Initiative, a national prospective study. “We looked specifically at the women who had been recruited from the San Diego metropolitan area. In those women, we were able to then calculate the distance between where they lived and the nearest major roadway. In this study, major roadways included freeways, freeway ramps and major arterial roadways.”
The researchers then looked at which of the 5,400 women had hypertension — which the researchers defined using blood pressure data and physician diagnoses — when they were recruited by the Women’s Health Initiative, Wellenius said.
To determine the effects of living near roadways on hypertension, the researchers used models that adjusted for multiple caridovascular risk factors, including age, race, smoking history, alcohol consumption, education, household income, marital status and certain markers of neighborhood socioeconomic status. Wellenius added that additional analyses “adjusted for body mass index, diabetes, physical activity and total cholesterol” and yielded comparable results.
Modern computing technology made conducting these large-scale analyses relatively easy, said Melissa Eliot, the data manager for the University’s Center for Environmental Health and Technology.
Despite the researchers’ adjusting their models to control for multiple variables, Michael Marmor, a professor of population health and environmental medicine at New York University’s School of Medicine, said the researchers’ results “may be affected by what is called ‘residual confounding.’”
For example, Marmor said, in real estate, location determines property value. It is possible that San Diego properties of slightly lower value may be located closer to major roadways, so people of lower socioeconomic status might live there. Looking at this factor, the results might not clearly show whether hypertension correlates with proximity to roadways or socioeconomic status.
“Socioeconomic status is especially important for this study, as socioeconomic status may be associated with obesity and general health status, and those, in turn, may be associated with high blood pressure,” Marmor said. “I question whether a statistical model like the one used by the investigators can adequately adjust away all possible confounding due to socioeconomic status.”
The researchers plan to broaden the scope of their study with future work. They plan on “looking at this at the national level to see if the effects of living very near a major roadway are similar in other parts of the country,” Wellenius said.
Though the study provides insights about how roadways may impact health in postmenopausal women, other demographics have not yet been examined, Wellenius said.
“I think what you have to keep in mind is that this particular study was in postmenopausal women that were all 50 and older, so whether this is of concern to younger individuals or men of any age is really an open question,” he said. “Additional studies will be needed to clarify what other segments of the population are also at risk.”
But, Wellenius added, “I think there’s increasing evidence that the urban environment can have effects on your health, and whether that be from living near toxic wastes or living near roadways with their traffic,” adding that his study about traffic is only “a small piece” of the larger issue of how a city environment impacts the body.
People who live near major roadways and who are concerned about negative impacts on their health should “lower their baseline risk of hypertension” by exercising, maintaining a healthy diet and weight, listening to advice from doctors and not smoking, Wellenius said.
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