A recent study published in the British Journal of Sports Medicine reports that physically active women are 25% less likely to develop breast cancer. The researchers, hailing from Canada and Australia, note however that some groups have a greater likelihood of seeing preventive benefits than others.

A woman's level of protectiveness against breast cancer is affected by several factors. Some of these include the type of physically activity undertaken, when in the woman's life that she is active, and the woman's body mass index (BMI) - a measure of a person's weight adjusted for height. The researchers found the lowest risk group for breast cancer to be lean women who play sports and remain physically active in their spare time. These traits were strongly related to a preventive quality, especially for women who have been through menopause.

Conclusions for this study came from a meta-analysis of 62 papers that focused on physical activity and its association with the risk of breast cancer. The researchers sifted through the various findings of these studies to see how the risk of breast cancer was linked to the type and intensity of physical activity, when the activity was performed, and additional factors.

Though all activity types reduced breast cancer risk, the most physically active women were least likely to develop the cancer. Recreational physical activity seemed to reduce the risk more than activities that were associated with a job or with housework. Additionally, they noted that moderate and vigorous activity had basically the same benefits.

Post-menopausal women who had been very active during their lives were found to have the lowest breast cancer risk, and post-menopausal activity had a greater impact than activity performed earlier in life. Among obese women, physical activity did not reduce risk, whereas the greatest reduction in risk was seen in lean women. A lower breast cancer risk was also noted in women who were mothers, did not have a family history of the disease, were not white, and had estrogen receptor negative tumors.

"Further observational epidemiological research is needed to clarify the biological mechanisms underlying the association between physical activity and reduced breast cancer risk, especially with regard to the type, duration and intensity of activity and to explain differences in population subgroup effects. We can expect continuing advances in knowledge of these mechanisms as the field is moving forward with important developments in methods, including improvements in physical activity assessment, animal models, development of suitable biomarkers and incorporation of new technologies such as microarrays that can examine gene and protein expression changes in response to physical activity," conclude the authors.

Physical activity and breast cancer risk: impact of timing, type and dose of activity and population subgroup effects
C M Friedenreich, A E Cust
British Journal of Sports Medicine
(2008)
doi:10.1136/bjsm.2006.029132
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Written by: Peter M Crosta