The more physical activity a person does, the lower the risk of a stroke, a review of 23 international studies finds.

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“Reduction in stroke risk is another reason to participate in regular and moderate-to-high intensity physical activity,” said the report in the October edition of the American Heart Association journal Stroke.

It’s known that exercise reduces the risk of heart disease, the leading cause of death in the United States. But researchers have done less work on stroke, the third-leading cause.

The researchers drew data from some of the largest examinations of the effects of physical activity on health. Among these are the National Health and Nutrition Examination Survey by the Centers for Disease Control and Prevention, and three databases run by Harvard University researchers, which followed male doctors, female nurses and male Harvard alumni. These studies previously had helped to establish the benefit of exercise against heart disease.

The analysis found that highly active people had a 27 percent lower risk of having a stroke or dying if they had one, compared with people who got little or no physical activity. Moderately active people had 20 percent lower risk.

Although the definitions of highly active varied from study to study, jogging 15 to 20 minutes a day on most days would qualify as highly active, said Chong Do Lee, lead author of the report and an assistant professor of sport and exercise sciences at West Texas A&M University. Moderate activity would be the equivalent of brisk walks of 30 minutes a day on most days, he said.

The analysis did not show why physical activity reduces stroke risk, but it’s probably due to the same factors that affect heart disease risk, Lee said.

Heart disease and stroke result from damage to small blood vessels. Physical activity protects against damage to those vessels by such means as lowering blood pressure and cholesterol levels, improving the ability of the vessels to widen when more blood flow is needed, and reducing the likelihood of a clot inside a blood vessel.

The findings demonstrate that “one of the most simple, natural and cheapest ways of preventing a stroke is to exercise regularly,” an editorial in the journal said. And the analysis also shows that people who do more exercise get more benefit, wrote Dr. Michael Brainin of Donauklinikum and Danube University in Austria.

Even though moderate activity is good, people should not stop there. “It is now established beyond reasonable doubt that high-level physical activity is to be strongly recommended,” Brainin said.

“This paper fills a good void,” said Dr. Paul D. Thompson, director of preventive cardiology at Hartford Hospital in Connecticut, who was not part of the research project.

The benefits of physical activity on heart disease have been easier to study because there is more heart disease, which made it necessary to comb through a lot of data to amass enough stroke cases for meaningful conclusions, Thompson said.

However, the article’s findings relied on participants’ responses to questionnaires. And it would be better if a large study had people exercise, so scientists could watch what happens to their stroke risk, Thompson said. But such a project would be very expensive. “There will never be such a giant study, I don’t think,” he said.

© 2012 The Associated Press. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.

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