Women who take brisk walks regularly have a lower risk of developing breast cancer after menopause - and it’s never too late to start, new study findings suggest.

Reviewing data collected from nearly 100,000 postmenopausal women, researchers found that women who scheduled at least an hour of brisk walking per day (or an equivalent amount of activity) were 15 percent less likely to get breast cancer than women who walked less than one hour per week.

And those who got little exercise but boosted their activity after menopause were 10 percent less likely to develop the disease than those who stayed inactive.

Overall, five in 100 women got breast cancer over 20 years.

There are many risk factors for breast cancer that women have no control over, such as family history or the age at which they begin menstruating, study author Dr. A. Heather Eliassen told Reuters Health.

Physical activity “is one of the few breast cancer risk factors that women can do something about,” she said. “And it’s never too late.”

There is a growing body of research showing that very active women are less likely to develop breast cancer than their sedentary peers. But less is known about the effect of moderate exercise, and whether less active women who start exercising get similar benefits.

Previous studies about the benefits of exercise on breast cancer risk are also difficult to compare side-by-side, said Dr. Michael Leitzmann of Regensburg University in Germany, who was not involved in the study.

Many are designed differently, for instance, or ask different questions about how much activity women are getting.

However, “the majority of evidence really lies in favor of risk reduction with physical activity,” Leitzmann told Reuters Health.

In the new study, published in the Archives of Internal Medicine, Eliassen and her team at Harvard reviewed data collected from 95,396 women who were followed for 20 years. At regular intervals, women reported how active they were, and the types of exercise they chose to do.

The researchers found that regular exercise was associated with a lower risk of breast cancer even after removing the potential influence of drinking and weight.

Eliassen and her team also looked at which activities - such as swimming, hiking, or jogging - were associated with the lowest risk, and found that brisk walking appeared to be the most protective against breast cancer. This was also the most common type of exercise, Eliassen explained, which may have skewed the findings.

What’s encouraging, she added, is that women didn’t need to engage in vigorous workouts to see a benefit - it’s enough to simply walk at a brisk pace, roughly three to four miles per hour, in which it’s harder to hold a conversation than when casually strolling.

The study’s design did not allow the authors to prove whether walking caused less breast cancer, because there may be other factors common to women who walk more that made them less likely to develop it.

Still, the results are suggestive, they note. However, it remains unclear why exercise would protect against breast cancer, Eliassen said.

Research has shown that activity reduces estrogen in the blood, which can affect breast cancer risk. But in this study, exercise also reduced the risk of breast cancers that aren’t influenced by estrogen, suggesting there are other explanations.

“Physical activity also has an effect on chronic inflammation, and insulin sensitivity,” Eliassen said. “So there are other ways in which physical activity could be acting” on breast cancer risk.

SOURCE:  Archives of Internal Medicine, October 25, 2010.