HYPERTENSION RISK RISES CLOSER TO MAJOR ROAD WAYS
In a newly
published analysis, the risk of high blood pressure among 5,400 post-menopausal
women was higher the closer they lived to a major roadway. The result, which
accounts for a wide variety of possible confounding factors, adds to concerns
that traffic exposure may present public health risks.
A new study in the Journal
of the American Heart Association reports a significant association
between living near a major roadway and the risk of high blood pressure.
The Brown
University-led analysis of data from 5,400 post-menopausal women in the San
Diego metropolitan area found that women who lived within 100 meters of a
highway or major arterial road had a 22-percent greater risk of hypertension
than women who lived at least 1,000 meters away. In a range of intermediate
distances, hypertension risk rose with proximity to the roadways.
Put in epidemiological
terms, a 58-year-old woman in the study who lived close to a major road had the
blood pressure risk of a 60-year-old woman who lived far from one. The elevated
risks reported in the study statistically account for a wide range of
confounding cardiovascular risk factors including age, demographics, health,
and lifestyle and even local fast food availability.
Hypertension is an
underlying factor for some cardiovascular diseases. For that reason, the
increased likelihood of hypertension reported in the new study may help explain
prior findings of associations between proximity to major roadways and
cardiovascular diseases such as stroke. A few studies, mostly in Europe, have
also tested the association between roadway proximity and hypertension, but
results have been mixed.
"I think in the
United States this study does tip the scale in favor of being concerned about
the urban environment and how we develop our cities and our transportation
systems," said study corresponding author Gregory Wellenius, assistant
professor of epidemiology in the Brown University School of Public Health.
"There are a lot of new developments going up right near highways. One has
to start thinking about what are the associated health effects with that."
Assessing the
association
The study data comes
from the Women's Health Initiative, a study funded by the National Heart Lung
and Blood Institute that enrolled tens of thousands of participants in the mid
1990s including more than 5,600 in San Diego County. The study gathered data on
a wide variety of personal health and demographic measures, including where
participating women lived, their blood pressure and other key attributes.
Wellenius, lead author
and graduate student Kipruto Kirwa, and their co-authors took this dataset and
used mapping software to measure the distance from each woman's home to a major
roadway. They also consulted a database to determine each neighborhood's
abundance of supermarkets and fast-food restaurants to determine who lived in a
so-called "food desert" where unhealthy food options were relatively
many and healthier ones relatively few.
They then looked at
the association between the prevalence of high blood pressure and distance from
the highway (in ranges of less than or exactly 100 meters, between 100 and 200
meters, 200 to 1,000 meters and more than 1,000 meters).
In three levels of
analysis, the researchers controlled for more and more possible confounding
factors. In all, they controlled for age, ethnicity, smoking status, education,
household income, cholesterol, body-mass index, diabetes history, physical
activity level, and local food quality.
After all that, they
found the odds of hypertension were 1.22 to 1 for those living closest, 1.13 to
1 for those between 100 and 200 meters, and 1.05 to 1 for those between 200 and
1000 meters from a major roadway. These odds are indexed such that 1 represents
the prevalence risk of those living more than 1,000 meters from a major
roadway.
Wellenius acknowledged
that because the study only measured who had hypertension and where they lived
at one moment in time, it does not necessarily show a causal link. The study
also does not shed light on what specifically about proximity to the road could
cause hypertension. It could be airborne pollutants or noise or both -- or
something else. But prior studies have shown specific physiological effects
from pollution and noise that could have direct causal relevance to
cardiovascular disease.
Wellenius cautioned
that hypertension, even when treated, still carries an elevated risk of
cardiovascular disease. The best policy, he said, is therefore prevention.
"The public
health message is that we need to take into consideration the health of the
population when planning neighborhoods, when planning transportation systems,
and when deciding where new highways are going to go, and how we might be able
to mitigate traffic or its effects," Wellenius said.
In addition to Kirwa
and Wellenius, other authors are Melissa Eliot, Yi Wang, and Dr. Charles Eaton
of Brown; Marc Adams of Arizona State University; and Cindy Morgan, Jacqueline
Kerr, Gregory Norman, and Dr. Matthew Allison of the University of
California-San Diego.
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