Nutrition Notes
Week of February 2, 2009
Contact: Sarah Wally, (202) 328-7744

New Reports on Physical Activity and
Breast Cancer Prevention

Karen Collins, MS, RD, CDN
American Institute for Cancer Research

New research is adding more insight into the link between walking and other forms of physical activity and lower risk of breast cancer. A landmark report on diet, activity and the prevention of cancer from the American Institute for Cancer Research (AICR) noted that increased physical activity probably lowers risk of postmenopausal breast cancer and potentially risk of pre-menopausal breast cancer as well. This week, I’ll share some of the most-commonly asked questions regarding cancer and physical activity:

Is it too late to make a difference after years of sedentary living? Research suggests that it’s never too late to start making changes to reduce your cancer risk. In one recent Japanese study, the most active women had less than half the risk of postmenopausal breast cancer than the least active women. Study participants were 40 to 69 years old at the start of the study. In another recent study from Germany, physical activity after age 50 showed an even stronger effect in reducing risk of postmenopausal breast cancer than physical activity at ages 30 to 49.

Is being active worth it if I don’t lose weight? While many people connect exercise to weight control, physical activity protects our health in many ways. Recent studies support findings that physical activity helps lower postmenopausal breast cancer risk both through assisting weight control and more directly. Though studies are not universally consistent, in both studies noted above, the link between more activity and less breast cancer was independent of weight loss.

How much activity will it take? Here’s where it gets harder to interpret because studies measure and categorize activity level in different ways. In the Japanese study mentioned above, women needed to accrue at least one hour of walking daily plus at least one hour of other exercise each week before they showed a significantly lower risk. In the German study, a 21 to 25 percent lower risk of postmenopausal breast cancer was seen in women who got the most leisure time physical activity – the equivalent of at least two hours a day of brisk walking.

Although these recent studies don’t show a clear decreased risk of breast cancer until you reach an hour or more of daily activity, other analyses reveal that even modest activity can impact risk. The AICR second expert report shows that risk of postmenopausal breast cancer drops by three percent for the equivalent of about two hours of moderate walking weekly. A previous analysis of 48 studies looking at risk of pre- and post-menopausal breast cancer showed a 12 percent drop in risk with two hours of moderate exercise weekly. And an important reminder: If you can’t find a large block of time in your week, benefits are seen when activity is broken up into 10- or 15-minute blocks of time.

Is more intense activity better? Several studies, including the Japanese study discussed here, show added protection from breast cancer when women include at least some vigorous activity like jogging, hill walking or aerobics classes each week.

We clearly need more research to resolve some of the more detailed questions about activity and breast cancer risk. But meanwhile, health experts acknowledge that the payoffs of regular physical activity are substantial. And as you begin to discover just how good it makes you feel, don’t hold back, because the more, the better (within reason).

Our Mission: The American Institute for Cancer Research champions the latest and most authoritative scientific research from around the world on cancer prevention and survival through diet, weight and physical activity, so that we can help people make informed lifestyle choices to reduce their cancer risk.

We have contributed over $105 million for innovative research conducted at universities, hospitals and research centers across the country. Find evidence-based tools and information for lowering cancer risk, including AICR’s Recommendations for Cancer Prevention, at

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