THURSDAY, Oct. 27, 2005 (HealthDay News) -- Air pollution increases the risk of ischemic stroke by a small but significant amount, a new study finds.
Medicare records on more than 150,000 people hospitalized for stroke in nine U.S. cities found that an increase in air pollution from the lowest to the highest concentrations was associated with a 1.03 percent increase in incidence, according to the report in the Oct. 27 issue of Stroke.
"That doesn't sound like much, a small increase, but if you consider how many people are at risk for stroke, the absolute increase in incidence can be quite high," said study author Gregory Wellenius, a postdoctoral fellow in cardiology at Beth Israel Deaconess Medical Center in Boston.
Some 700,000 American suffer strokes each year, with the most common form being ischemic stroke, which occurs when a clot blocks a brain artery, according to the American Stroke Association.
The study concentrated on small particle pollutants, which are spewed from sources including car and truck exhausts, power plants and refineries. But it found a similar increase in risk for other pollutants -- carbon monoxide, nitrogen dioxide and sulfur dioxide.
Many studies have established a link between polluted air and heart attacks, heart failure and other cardiac problems. And previous studies have also pointed to an increased risk of stroke, Wellenius said. But this is the first to distinguish between ischemic strokes and hemorrhagic strokes, which occur when a blood vessel ruptures.
The study did not find an increased rate of hemorrhagic stroke associated with heavily polluted air. That could be due to the relatively small number of hospital admissions for such strokes, which makes it difficult to establish statistical significance, Wellenius said.
The researchers theorized that polluted air might increase ischemic stroke risk the same way it increases heart disease risk -- by promoting the formation of blood clots and causing fatty plaques in arteries to rupture.
More work is needed to firm up the association, Wellenius said. The current study was limited to people old enough to be in Medicare, "and we need to replicate this study in other populations," he said. A closer look at the effects of pollutants other than small particles is also needed, he added.
The study has strong regulatory implications, said Frank O'Donnell, president of Clean Air Watch, a nonprofit environmental organization.
The U.S. Environmental Protection Agency is under a court order to make a ruling by December on whether current federal standards are adequate to protect health, he said, and the study "is further evidence that fine-particle pollution is a significant public health risk."
"We should be doing much more to try to reduce this dangerous pollution," O'Donnell said.
Fine-particle pollution causes an estimated 20,000 premature deaths in the United States each year, he said. The EPA has proposed standards to reduce such pollution by diesel engines, "but they won't reach their peak potential until 2030," O'Donnell explained.
More information
Facts about the health effects of air pollution and how to protect against them are provided by the American Academy of Family Physicians.
