Cancer
Physical activity cuts breast cancer risk
By Sue Mueller
May 14, 2008 - 12:35:10 PM

WEDNESDAY May 14, 2008 (foodconsumer.org) -- Women with regular physical activity are more likely to have lower risk of breast cancer, according to a new report published in the May 12, 2008 issue of British Journal of Sports Medicine.

The report said physical activity offered greatest benefits to postmenopausal women and those who with normal body weight.  And certain physical activities such as recreational activity were more beneficial than others such as work-related physical activity.

For the report, Dr. C. M. Friedenreich, from the Alberta Cancer Board in Calgary, Canada, and Dr. A. E. Cust, from the University of Melbourne in Australia reviewed 62 studies to examine how physical activity would affect risk of breast cancer.

The authors found 47 studies indicated that increased physical activity cut the risk of breast cancer by 25 to 30 percent. In 28 studies, the authors found the risk of breast cancer varied with the intensity of physical activity with increased activity leading to lower risk.

The types of physical activities made a difference.  Activities that offered highest levels of reduction in breast cancer risk included recreational activity, vigorous activities, lifetime or later life activity.

Women who benefited most from physical activity included postmenopausal women, women with a normal BMI, non-white women, and those who had no family history of breast cancer.

Physical activity reduced risk of hormone receptor-negative tumors more significantly than hormone receptor positive tumors.

The authors said more studies are needed to clarify the mechanism underling the association between physical activity and reduced breast cancer risk.

The following is cited from cancer.gov regarding the association of physical activity and breast cancer risk, updated on April 23, 2008.

How can physical activity reduce breast cancer risk?

The association of physical activity with breast cancer incidence has been extensively studied with over 60 studies published in North America, Europe, Asia and Australia. Most studies indicate that physically active women are at lower risk of developing breast cancer than inactive women; however the amount of risk reduction achieved through physical activity varies widely (between 20-80%) (6,7).

While most evidence suggests that physical activity reduces breast cancer risk in both premenopausal and postmenopausal women (6), high levels of moderate and vigorous physical activity during adolescence may be especially protective. Although a lifetime of regular, vigorous activity is thought to be of greatest benefit, women who increase their physical activity after menopause may also experience a reduced risk compared to inactive women.

A number of studies also suggest that the effect of physical activity may be different across levels of BMI, with the greatest benefit seen in women in the normal weight range (generally a BMI under 25 kg/m-squared) in some studies. Existing evidence shows decreasing risk of breast cancer as the frequency and duration of physical activity increases. Most studies suggest that 30-60 minutes per day of moderate- to high-intensity physical activity is associated with a reduction in breast cancer risk(4, 6).

Researchers have proposed several biological mechanisms that may explain the relationship between physical activity and breast cancer development. Physical activity may prevent tumor development by lowering hormone levels, particularly in premenopausal women, lowering levels of insulin and insulin-like growth factor I (IGF-I) improving immune response, and assisting with weight maintenance to avoid a high body mass and excess body fat (7).