Exercise Reduces Breast Cancer Risk

Women who are physically active have lower levels of estrogen and its breakdown products in their bodies, which helps to explain why exercise may reduce breast cancer risk. 

Cher Dallal, from the US National Cancer Institute (Maryland, USA), and colleagues evaluated 540 Polish women, ages 40 to 74 years, who were enrolled as healthy control patients in the NCI Polish Breast Cancer Study. None of the patients was on hormone therapy. The women engaged in a range of physical activity. For seven days, they wore an accelerometer on their waist while awake, which measured overall activity. The women also collected 12-hour urine samples. 

The researchers measured the hormones estradiol and estrone, along with different estrogen breakdown products, in the urine; they found that physical activity was associated with lower levels of the main estrogens, and that activity also was associated with increased metabolism of some of the breakdown products.  Writing that: “Our findings with accelerometer-measured physical activity are consistent with prior studies reporting a reduction in estrogen levels with increased activity,” the study authors submit that: “our results suggest that increased physical activity may lower endogenous estrogens by increasing hydroxylation, and subsequent metabolism, of estrogens.”

Since most tumors are estrogen receptor positive, it is important to understand that estrogen metabolism is an important component to proper risk evaluation. Estrogen dominance or progesterone deficiency has been implicated in higher incidence of breast cancer.