Several observational studies suggest a strong link between exercise and lower risk of some cancers. This appears most true for breast cancer. We now have at least one explanation why exercise lowers breast cancer risk. Exercise alters the metabolism or breakdown of estrogen into a good metabolite. This healthy change in estrogen related to exercise leading to reduced cancer risk was recently reported in a study published in Cancer Epidemiology, Biomarkers, & Prevention. This study is the first to show that aerobic exercise alters the way the body metabolizes estrogen.
The study involved 391 healthy but sedentary premenopausal women as a part of the Women in Steady Exercise Research or WISER clinical trial. The women were divided into 2 groups – 179 women in a control group and 212 women in the exercise group. The women were matched for age and body mass index (BMI) as higher breast cancer risk is seen in older women and women with higher body fat.
Estrogen and Its Metabolites
In women there are 3 main estrogens; estrone (E1), estradiol (E2), and estriol (E3). Most estrogen is made in the ovaries but some is made from the conversion of testosterone to estrogen (women make testosterone, too). The enzyme called aromotase makes this conversion from estrogen to testosterone and is higher in men and women who have more body fat. Estrogen has proliferative effects on the uterus and breasts. This means it encourages tissue growth. This growth is counterbalanced by progesterone in women. Too much estrogen relative to progesterone (estrogen dominance) increases breast cancer risk as well as endometrial cancer risk.
Estrogen is broken down into various metabolites. One metabolite is called 2-hydroxyesterone (2-OHE1) and aother is 16 alpha-hydroxyesterone (16 alpha-OHE1). 2-OHE1 is associated with lower breast cancer risk while 16 alpha OHE-1 is linked to higher breast cancer risk. Too much 16 alpha OHE-1 to 2-OHE1 is linked to higher breast cancer risk.
Aerobic exercise leads to increase estrogen breakdown to 2-OEH1 reducing breast cancer risk. Exercise also can lead to fat loss which reduces the overall amount of estrogen a woman makes and that might be another factor that exercise reduces cancer risk in general. Also, fat tissue is highly inflammatory and inflammation increases the cancer risk providing a third mechanism by which exercise reduces breast cancer risk.
Cruciferous vegetables minimize cancer risk by converting more estrogen into the safer 2-OHE1 metabolite. Supplements like DIM and indole-3 carbinol do the same potentially reducing breast cancer risk.
Many studies on cancer and breast cancer involved simply walking 30 minutes every day. So you don’t have to do much exercise to lower your breast cancer risk. So cut your breast cancer risk by becoming more physically active.