Physical activity's effect on breast cancer varies

The results of a literature review of published studies confirm that while all women are likely to reduce their risk of breast cancer with regular physical activity, certain subgroups benefit more than others.
According to the report posted online by the British Journal of Sports Medicine, postmenopausal women and those with a normal body mass index (BMI) are among the groups that achieve the greatest risk reduction with physical activity. BMI is the ratio of height to weight.
The findings also indicate that certain activities influence the risk reduction more than others. For instance, recreational physical activity cut the risk of breast cancer to a greater extent than did work-related activity.
Dr C. M. Friedenreich, from the Alberta Cancer Board in Calgary, Canada, and Dr A. E. Cust, from the University of Melbourne in Australia, examined how the timing, type, and level of physical activity affects the breast cancer risk. Their literature search identified 62 studies.
Forty-seven of the 62 (76 percent) studies indicated there was an anti-breast cancer effect for increased physical activity, with typical risk reductions of 25 percent to 30 percent, the authors report. In 28 of 33 studies, they found evidence of a dose-response effect, which means more exercise correlated with more benefits.
In terms of activities, recreational activity, vigorous activity, and lifetime or later life activity provided the strongest reductions in breast cancer risk. In addition to postmenopausal women and those with a normal BMI, other subgroups most likely to benefit from physical activity were non-white women, women who half given birth, and those without a family history of breast cancer.
Exercise also had a greater effect in reducing hormone receptor-negative tumours than hormone receptor-positive tumours, the findings indicate.
"Further observational epidemiological research is needed to clarify the biological mechanisms underling the association between physical activity and reduced breast cancer risk," Friedenreich and Cust conclude, "especially with regard to the type, duration and intensity of activity and to explain differences in population subgroup effects."