Researchers at Beth Israel Deaconess Medical Center (BIDMC) and the Harvard School of Public Health (HSPH) examined air quality on a total of 37,000 days in nine cities. Risk of hospitalization for ischemic stroke was 1 percent higher on days with relatively high levels of air pollution, compared with low-air pollution days, reports lead author Gregory Wellenius, ScD, postdoctoral fellow in cardiology at BIDMC.

"Stroke is the third leading cause of death in the US, affecting more than 700,000 individuals each year.

"Air pollution has been shown to trigger heart attacks and to aggravate the conditions of patients with congestive heart failure," says Mittleman, who is also an associate professor of medicine at Harvard Medical School.

The researchers also looked at the incidence of hemorrhagic stroke, which is caused by bleeding in the brain, during the same "high pollution" days, notes Wellenius, but found no association between the two.

The authors analyzed hospital admissions among a group of Medicare patients with an average age of 79. Seventy-five percent of the patients were white, and 61 percent were female. Their findings showed that during the course of their study, there were 155,503 hospital admissions for ischemic stroke.

03 percent rise in ischemic stroke on the days with the highest pollution measures.

The authors say that future research will focus on finding out which pollutants are most toxic, as well as which patients are at greatest risk for health problems stemming from air pollution."