Air Pollution May Increase Stroke, Heart Attack Risk

February 14, 2012


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By Anne Harding

TUESDAY, February 14, 2012 ( — A brief uptick in traffic-related air pollution may be enough to increase a person’s short-term risk of stroke, new research suggests.

An analysis of 10 years of data from a major Boston stroke center has found that strokes are more likely to occur immediately following 24-hour periods in which air quality drops into the range the Environmental Protection Agency (EPA) considers “moderate.”

“At levels that the EPA considers to be generally safe, we found an important effect of ambient air particles, which is one of many pollutants in the air, but an important one,” says study coauthor Gregory A. Wellenius, Sc.D., an assistant professor of community health at Brown University Medical School, in Providence, R.I. Wellenius collaborated with researchers at Beth Israel Deaconess Medical Center and the Harvard School of Public Health, both in Boston.

In their report, published Monday in the Archives of Internal Medicine, Wellenius and his colleagues compared 1,705 stroke cases in the Boston area with detailed data on the day-to-day levels of various airborne pollutants, including vehicle emissions such as particulate matter, black carbon, and nitrogen dioxide.

After taking into account each patient’s medical history, the researchers concluded the odds of having a stroke were 34% higher following a day of “moderate” air quality than following a “good” air day.

Based on this finding, they estimate that a 20% reduction of levels of fine particulate matter would have prevented 6,100 of the 184,000 stroke hospitalizations that occurred in the northeastern United States in 2007.

The study doesn’t show that air pollution directly triggers strokes, although the researchers say that is biologically plausible. And because this is just one study in one location, Wellenius says, the findings don’t necessarily argue for tighter restrictions on U.S. air quality standards.

Still, he says, “if this was replicated in other parts of the country and in other populations, and similar findings came out, it would be a good idea to review the health warnings that come with certain particle levels.”

A second study, appearing this week in the Journal of the American Medical Association, provides additional evidence that air pollution may increase cardiovascular risk. In that study, a team of French researchers re-analyzed data from 34 previous studies conducted around the world. Most of the studies used methods similar to those of Wellenius and his team.

Higher levels of airborne pollutants—including particulate matter, carbon monoxide, nitrogen dioxide, and sulfur dioxide—were associated with a slight increase in the short-term risk of heart attack, the study found. As with Wellenius’ study, the researchers observed an uptick in heart risk even at pollution levels classified as safe by the World Health Organization.

Next page: How pollution harms the heart

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