Even Moderate Air Pollution Can Raise Stroke Risks

Ominous clouds

This article is written by David Abel for Boston.com:

Car exhaust and other air pollution, even at levels considered safe by federal regulations, may substantially increase the risk of a stroke, a research team from Beth Israel Deaconess Medical Center reported yesterday.

After reviewing the medical records of more than 1,700 stroke patients in the Boston area over 10 years, the researchers found a 34 percent increase in the risk of ischemic strokes on days with moderate air quality, compared with days when the air was rated good by the US Environmental Protection Agency. Ischemic strokes occur when a blood clot blocks blood flow to part of the brain.

On days with moderate air quality, levels of fine particulate matter are higher but within allowable limits.

“This is a significant study because we have documentation that the risk of stroke can be elevated when the air quality is still within the guidelines set by the current EPA regulations,’’ said Dr. Murray A. Mittleman, an author of the study who teaches at Harvard Medical School and works in the CardioVascular Institute at Beth Israel Deaconess. “This implies that the current regulations can be strengthened further to prevent these catastrophic health events.’’

The researchers said the EPA should also revise the language it uses to describe the health consequences of moderate air quality to reflect the apparently increased stroke risk.

The federally funded study, published in the journal Archives of Internal Medicine, focused on particles with a diameter of less than 2.5 millionths of a meter, which come from sources including power plants, factories, automobiles, and burning wood.

They can lodge deep in the lungs and have been linked to difficulty breathing in asthmatics and heart attack patients.

The researchers matched the onset of stroke symptoms in patients to hourly measurements of air pollution taken at the Harvard School of Public Health’s environmental monitoring station, which was within 13 miles of 90 percent of the stroke patients’ homes.

They estimated the hour the stroke symptoms occurred, rather than relying on when patients were admitted to the hospital. They also included only strokes confirmed by neurologists, rather than going by insurance billing records.

“We think that this study is novel in that it has high-quality data on both air pollution exposure and stroke diagnosis,’’ said Gregory Wellenius, another author of the study and an assistant professor of community health at Brown University.

The researchers calculated that the peak risk to patients from pollution exposure occurs 12 to 14 hours before a stroke. They also found heightened stroke risk was more closely tied to levels of two air pollutants from vehicles, black carbon and nitrogen dioxide, than to pollution from other sources.

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TOPICS: Pollution