Vigorous exercise most days of the week can reduce the risk of stroke, a new U.S. study finds.

Researchers from the University of Alabama at Birmingham analyzed data from 27,000 adults ages 45 and older in the US from the Reasons for Geographic and Racial Differences in Stroke (REGARDS) study cohort.

Subjects were classified as being inactive (no exercise), moderately active (exercising one to three times per week), or vigorously active (exercising more than four times per week), and they were followed for an average of 5.7 years.

Being inactive was associated with a 20 per cent increased chance of stroke, while those who exercised vigorously were less likely to experience a stroke or mini-stroke, the researchers said.

The results were especially true for the men, but for the women, the relationship between exercise frequency and stroke were less clear. "There has been some research to suggest that women perhaps benefit from less intense exercise, like walking, but seeing as we didn't ask this question in our study we really can't speculate any more than that," study lead author Michelle McDonnell told HealthDay.

While prior research has already found that exercise can directly reduce risk of stroke by improving the health of blood vessels and indirectly by improving related risks such as high blood pressure and obesity, HealthDay reports, this study is unique in that it tracks a diverse population of people over time.

"The protective effect of intense physical activity may be through its impact on traditional risk factors such as hypertension and diabetes," explained Dr. Virginia Howard, professor of epidemiology and senior study author.

"These findings confirm past results of studies done in only men or only women in limited geographical areas," she said. "By using the REGARDS cohort, our study was able to use a larger and more diverse population to show that participating in regular physical activity is associated with lower stroke risk."

Findings were published Thursday online in the journal Stroke.