Physical activity may reduce breast cancer risk

Women who are physically active may have a risk of breast cancer that is 25% lower than sedentary women, according to an article published online May 16 in the British Journal of Sports Medicine.

Christine M. Friedenreich, PhD, of the Alberta Cancer Board in Calgary, Alberta, Canada, and colleagues reviewed all relevant published studies to examine the effect of exercise parameters on the risk of breast cancer in different population subgroups and to explore underlying biological mechanisms.

The researchers included 34 case-control and 28 cohort studies in the analysis. Forty-seven studies (76%) demonstrated a risk reduction associated with increased physical activity with a mean risk reduction of 25% to 30%. A dose-response effect was evident in 28 of 33 studies, the report indicates. More pronounced decreases in risk were seen with recreational activity, vigorous activity, and lifetime or later life activity. In addition, groups in which the risk reduction was greater included postmenopausal women, parous women, women with a normal body mass index, non-white racial groups, and women without a family history of breast cancer.

"The effect of physical activity on the risk of breast cancer is stronger in specific population subgroups and for certain parameters of activity that need to be further explored in future intervention trials," the authors conclude.

Friedenreich CM, Cust A. Physical Activity and Breast Cancer Risk: Impact of Timing, Type and Dose of Activity and Population Sub-group Effects. Br J Sports Med. Published Online First: 16 May 2008. doi:10.1136/bjsm.2006.029132.