By David Liu, PHD

Sunday July 1, 2012 (foodconsumer.org) -- University of North Carolina at Chapel Hill researchers conducted reported in the journal Cancer that physical activity, regardless of its intensity, before or after menopause may cut breast cancer risk. But this benefit can be negated by gaining body weight.

The study led by Lauren McCullough and colleagues showed women who exercised 10 to 19 hours each week were at 30 percent reduced risk for breast cancer, compared to those who did not excise as much.

Physical activity has been associated with reduced risk for breast cancer in previous studies.  But this study found that even mild physical excise can be beneficial.

The study involved 1,504 women with breast cancer with 233 cases noninvasive and 1,271 invasive, and 1,555 women without breast cancer who were 20 to 98 years old who were enrolled in the Long Island Breast Cancer Study Project, intended to investigate possible environmental causes of breast cancer.

The researchers found any amount of physical activity was associated with reduced risk for breast cancer.  And they found that exercise seemed to reduce the risk for hormone receptor positive breast cancers, the most commonly diagnosed tumor type in American women.

Physical activity is known to lower levels of hormones which are in most cases if not all promoting the development of breast cancer.  As a long term treatment, breast cancer patients are often given drugs that can reduce the cancer-promoting property of hormones such as estrogen.

"The observation of a reduced risk of breast cancer for women who engaged in exercise after menopause is particularly encouraging given the late age of onset for breast cancer," McCullough said.

Additionally, the researchers found that physical activity did not help women particularly postmenopausal women with excess body weight as much as it helped those with normal weight, suggesting that weigh gain can eliminate the beneficial effect of physical exercise on breast cancer  risk.

As many as 210,000 American women are expected to be diagnosed with breast cancer in 2012. This disease and complications are expected to kill about 40,000 women in the same year.