Exercise Lowers Breast Cancer Risk

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Exercise Lowers Breast Cancer Risk, Helps Bones, Studies Say By Todd Zeranski Dec. 11 (Bloomberg) -- Exercise may lower the risk of developing breast cancer after menopause, while also helping maintain bone density, according to two separate studies published in the Archives of Internal Medicine today. Post-menopausal women who exercise frequently or vigorously are 14 percent less likely to develop breast cancer than those who don't, Mayo Clinic researchers said. In another study, scientists at Washington University School of Medicine said exercising to lose weight maintained bone density, while dieting alone made bones weaker. Researchers said exercise reduced body fat, cutting a major source of estrogen associated with tumors in post-menopausal women. It also helped spur bone production, protecting against hip fractures and diseases such as osteoporosis. ``A common explanation given for the bone loss induced by weight loss is reduction in mechanical stress on the weight- bearing skeleton,'' scientists at Washington University School of Medicine said. ``Accordingly, the preservation of bone mineral density in the exercise group could be mediated through exercise-induced bone loading.'' The St. Louis, Missouri-based scientists studied 30 women and 18 men for a year. Those who restricted calories lost an average of 18 pounds (8.2 kilograms) and more than 2 percent of bone density in the lower spine, hip and upper femur, or thigh bone. Those who exercised lost an average of 15 pounds (6.7 kilograms) with no significant change in bone density. Cancer Findings Researchers at the Rochester, Minnesota-based Mayo Clinic examined the Iowa Women's Health Study, which included 41,836 post-menopausal women who were aged 55 to 69 in 1986. Questionnaires were completed frequently until 2002. Women with high physical activity levels, defined as vigorous exercise such as jogging or swimming more than twice a week or moderate exercise such as walking or golf more than four times a week, were 14 percent less likely to develop breast cancer, researchers said. Adjusting for body weight, people with high physical activity levels had a 9 percent lower risk. Lower body fat resulted in less estrogen, which may lead to fewer estrogen- and progesterone-receptor tumors, the study said. Tumors are classified as estrogen- or progesterone- receptor positive or negative based on whether the hormones bind to the surface of the tissue growth. ``Further studies are needed to confirm these novel findings,'' the researchers said. ``If found to be casually related to breast cancer, physical activity would have a substantial public health effect on the prevention of this disease, along with its other positive health benefits.'' The Mayo Clinic study was funded by the National Cancer Institute. The Washington University School of Medicine report was supported by the National Institutes of Health.