Research summary
August 2008
Young women may reduce risk of breast cancer with regular exercise
Researchers have found that young women who exercise regularly may substantially reduce their risk of developing breast cancer before menopause.
Background
Approximately one in four breast cancers are diagnosed in women before menopause. While there is an emerging consensus that exercise has a protective effect for postmenopausal breast cancer, there has been only limited evidence to suggest that there is a similar protective effect in premenopausal women.
Research findings
A recent study has suggested that women who exercise regularly between the ages of 12 and 35 have a significantly lower risk of breast cancer before menopause compared to young women who are less active. Researchers examined data from nearly 65,000 women enrolled in the Nurses’ Health Study II regarding their level of physical activity from age 12 onwards. The study found that those who were most physically active had a 23 percent lower risk of breast cancer before menopause than the least active women.
The levels of physical activity reported by the most active women were the equivalent of running 3.25 hours per week or walking 13 hours per week. The benefit of the exercise was not linked to a particular sport or intensity, but related to total activity. High levels of physical activity from ages 12 to 22 appeared to contribute most strongly to lower breast cancer risk.
National Breast and Ovarian Cancer Centre comment
These results add to the body of knowledge about exercise and risk of breast cancer. A number of studies have shown that regular physical activity totalling four or more hours per week reduces risk for breast cancer in post-menopausal women. This study shows that regular exercise may also reduce breast cancer risk in younger women.
There are a number of theories to explain this reduction in risk, including the effect of exercise on reducing a woman’s exposure to estrogen, which is known to play a role in the development of breast cancer. It also highlights a possible role of physical activity in enhancing the immune system’s defences against cancer.
Source
Maruit SS, Willett WC, Feskanich D, Rosner B, Colditz GA. A prospective study of age-specific physical activity and premenopausal breast cancer. Journal of the National Cancer Institute. 100 13 May 2008: 728-737.