Even moderate air pollution can up stroke risks

Washington, Feb 14 (ANI): Air pollution, even at levels generally considered safe by federal regulations, increases the risk of stroke by 34 percent, researchers have warned.

Beth Israel Deaconess Medical Center researchers, who studied more than 1,700 stroke patients in the Boston area over a 10-year period found exposure to ambient fine particulate matter, generally from vehicle traffic, was associated with a significantly higher risk of ischemic strokes on days when the EPA's air quality index for particulate matter was yellow instead of green.

Researchers focused on particles with a diameter of 2.5 millionths of a meter, referred to as PM2.5. These particles come from a variety of sources, including power plants, factories, trucks and automobiles and the burning of wood. They can travel deeply into the lungs and have been associated in other studies with increased numbers of hospital visits for cardiovascular diseases such as heart attacks.

"The link between increased stroke risk and these particulates can be observed within hours of exposure and are most strongly associated with pollution from local or transported traffic emissions," said Murray A. Mittleman, MD, DrPH, the study's senior author, a physician in the CardioVascular Institute at Beth Israel Deaconess Medical Center and an Associate Professor of Medicine at Harvard Medical School.

"Any proposed changes in regulated pollution levels must consider the impact of lower levels on public health," he added.

Gregory Wellenius, ScD, the study's lead author and an Assistant Professor of Community Health at Brown University added, "Considering that almost everyone is exposed to air pollution and is at risk for stroke, that's actually a pretty large effect."

Researchers analysed the medical records of more than 1,700 patients who went to the hospital for treatment of confirmed strokes between 1999 and 2008. They matched the onset of stroke symptoms in each patient to hourly measurements of particulate air pollution taken at the nearby Harvard School of Public Health's environmental monitoring station.

The team was able to calculate that the peak risk to patients from pollution exposure occurs 12-14 hours before a stroke. That information may be useful to researchers who want to trace how PM2.5 might be working in the body to increase the likelihood of stroke.

They also found that black carbon and nitrogen dioxide, two pollutants associated with vehicle traffic, were closely linked with stroke risk, suggesting that pollution from cars and trucks may be particularly important.

The finding that days of moderate air quality substantially elevate stroke risk compared to days of good air quality suggest that the Environmental Protection Agency may need to strengthen the language it uses to describe the health consequences of moderate air quality, researchers noted.

The finding has been published in the latest issue of the Archives of Internal Medicine. (ANI)