Exercise may cut breast cancer risk up to 30%

Physicians should encourage all women to be physically active, regardless of how much they weigh. That’s because exercise, particularly during the reproductive and postmenopausal years, might help lower breast cancer risk, says the lead author of a study on the topic.

Women who engaged in 10 to 19 hours of physical activity per week during their reproductive years or after menopause experienced a 30% reduced risk of developing breast cancer, according to a study published online June 25 in Cancer. Exercise also lowered cancer risk among overweight women who had a body mass index of 25 to 29.9 (link) .

Physical activity did not reduce the likelihood of developing breast cancer in obese women who had a BMI of 30 or higher. But being active did make their risk similar to that of women of normal weight who do not exercise, said lead study author Lauren E. McCullough, MSPH.

“The intensity of physical activity doesn’t need to be strenuous to receive health benefits,” said McCullough, a doctoral candidate in the Dept. of Cancer Epidemiology at the University of North Carolina Gillings School of Global Public Health. During their reproductive or postmenopausal years, women “can walk or do things that are considered moderate and get the same health benefits” as people who exercise vigorously, she said.

Researchers examined data on 1,504 women 20 to 98 who were newly diagnosed with breast cancer between Aug. 1, 1996, and July 31, 1997. The women were matched to a control group of 1,555 similarly aged females who had no history of breast cancer. Both groups were part of the Long Island Breast Cancer Study Project.

During that study, participants reported all recreational physical activity they participated in for at least one hour per week during three months. Such activity was defined as leisure-time exercise, which could include gardening, team sports, running and walking, McCullough said.

Researchers in the Cancer study found a 6% lower risk of developing breast cancer among premenopausal and postmenopausal women who reported ever engaging in recreational physical activity compared with females who never exercised.

A more significant finding was that women who exercised during their reproductive years or after menopause experienced the greatest reduction in breast cancer risk, McCullough said. A possible reason is that the high level of hormonal changes during those life stages might boost the benefits of physical activity, she said.

Weight gain after menopause, even among highly active women, however, seems to reduce or eliminate the benefits of exercise, the study said.

Breast cancer is the second-most common cancer among women after non-melanoma skin cancer, according to the Centers for Disease Control and Prevention. In 2008, there were 210,203 U.S. women diagnosed with breast cancer, and 40,589 females died of the disease, according to the CDC’s most recent data.