Women who are physically active a few times per week have lower risks of heart disease, according to a recent study.

Researchers found that middle-aged women reduce their risk of heart disease, stroke and blood clots by about 20 percent when they are active two to three times per week. Surprisingly, more frequent physical activity didn't result in further reductions in risk, researchers said.

"Inactive middle-aged women should try to do some activity regularly," Miranda Armstrong, the study's lead author and a physical activity epidemiologist at the University of Oxford in the United Kingdom, said in a statement. "However, to prevent heart disease, stroke and blood clots, our results suggest that women don't need to do very frequent activity as this seems to provide little additional benefit above that from moderately frequent activity."

Researchers found that women who performed strenuous physical activity -- enough to cause sweating or a faster heart beat -- two to three times per week were less likely to develop heart disease, strokes or blood clots compared to participants who reported little or no activity. Among active women, there was little evidence of further risk reductions with more frequent activity.

Participants included 1.1 million women in the United Kingdom with no history of cancer, heart disease, stroke, blood clots, or diabetes who joined the Million Women study in 1996-2001. Their average age when they joined the study was 56.

The women reported their level of physical activity at the beginning of the study and three years later. Researchers then examined hospital admissions and deaths in relation to participants' responses. Follow-up was, on average, nine year

The findings are detailed in the American Heart Association journal Circulation.