There is new hope for women interested in reducing their risk of breast cancer.
Dr. Christine Freidenreich and her team of researchers from the Alberta Cancer Board and the University of Calgary recently released the third part of a study that indicates regular physical activity can reduce a woman's risk of breast cancer by 40 per cent.
"Until now there have been very few modifiable behaviours that have been proven to have an effect," said Friedenreich. "Diet hasn't been shown to have an effect."
The study examined all types of activity during the lifetime of the subjects. Physical activity in the form of housework, exercise and employment were all considered as was the intensity, frequency and duration of each.
"It's important to make people understand that doing household work actually counts," said Freidenreich.
According to the study, any level of physical activity was beneficial. However, women who participated in an average of six hours a day achieved the maximum benefit.
"There was a dose-response effect," said Freidenreich. "But the response wasn't as statistically significant for those who excersised less."
The study examined the specific effects of exercise on post-menopausal women. Although the exact biological mechanisms that reduce the risk of breast cancer in post-menopausal women are not known, there are several hypotheses.
"We don't really know [how exercise reduces the risk of breast cancer]," said Freidenreich. "It is probably related to obesity. Women who are overweight after menopause are at an increased risk of breast cancer. However, women who are overweight pre-menopause are at a decreased risk."
She explained that the changes in risk may be due to how estrogen is produced in the body. In pre-menopausal women, the primary producer of estrogen is the ovaries and after menopause it is released by fat tissue. A surplus of estrogen has been identified as a factor in causing breast cancer.
The next step in the research will be to determine the biological mechanisms that reduce the risk of breast cancer and what type of activity provides the greatest benefits.