Posted on Jul 16, 2012, 6 a.m.
Physical activity – either mild or intense and before or after menopause – may reduce breast cancer risk, but substantial weight gain may negate these benefits.
Previously, a number of studies have suggested that physical activity reduces breast cancer risk. As well, maintaining a healthy, controlled weight has been shown to beneficially impact a person's risk for a variety of diseases. Lauren E. McCullough, from the University of North Carolina (North Carolina, USA), and colleagues studied 1,504 women with breast cancer (233 noninvasive and 1,271 invasive) and 1,555 women without breast cancer who were 20 to 98 years old and were part of the Long Island Breast Cancer Study Project. Women who exercised either during their reproductive or postmenopausal years had a reduced risk of developing breast cancer. Women who exercised 10 to 19 hours per week experienced the greatest benefit with an approximate 30% reduced risk. Risk reductions were observed at all levels of intensity, and exercise seemed to reduce the risk of hormone receptor positive breast cancers, the most commonly diagnosed tumor type among American women. Further, when the researchers looked at the joint effects of physical activity, weight gain and body size, they found that even active women who gained a significant amount of weight – particularly after menopause – had an increased risk of developing breast cancer, indicating that weight gain can negate the beneficial effects of exercise on breast cancer risk. Writing that: "[Regular physical activity]at any intensity level during the reproductive and postmenopausal years have the greatest benefit for reducing breast cancer risk,” the study authors warn that: "Substantial postmenopausal weight gain may eliminate the benefits of regular activity.”
Lauren E. McCullough, Sybil M. Eng, Patrick T. Bradshaw, Rebecca J. Cleveland, Susan L. Teitelbaum, Alfred I. Neugut, Marilie D. Gammon. “Fat or fit: The joint effects of physical activity, weight gain, and body size on breast cancer risk.” Cancer, 25 June 2012.