Even mild physical activity may reduce the risk of breast cancer, but substantial weight gain may negate these benefits, according to an analysis.
The findings indicate that women can reduce their breast cancer risk by exercising and maintaining their weight, researchers said.
Although previous studies showed physical activity reduces breast cancer risk, many questions have remained. For example, how often, how long and how intense does physical activity have to be to provide benefits? Also, do women with all body types experience a reduced risk when they exercise, and does exercise reduce the risk of all types of breast cancer?
To investigate, Lauren McCullough, a doctoral candidate at the University of North Carolina-Chapel Hill Gillings School of Global Public Health, and her colleagues looked for a link between recreational physical activity, performed at different time points in life, and the risk of developing breast cancer.
The study included 1,504 women with breast cancer (233 noninvasive and 1,271 invasive) and 1,555 women without breast cancer who were ages 20 to 98 and part of the Long Island Breast Cancer Study Project, an investigation of possible environmental causes of breast cancer.
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 about a 30% reduced risk. Risk reductions were observed at all levels of exercise intensity, and exercise seemed to reduce the risk of hormone receptor positive breast cancers, the most commonly diagnosed tumor type among American women.
The researchers also observed a reduced risk among women who engaged in exercise after menopause, which McCullough said is "particularly encouraging given the late age of onset for breast cancer," according to a news release.
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 eliminate the beneficial effects of exercise on breast cancer risk.
The study appeared June 25 on the website of Cancer, a peer-reviewed journal of the American Cancer Society. To read the abstract and access the study via subscription or purchase, visit http://bit.ly/Mv5I72.
