Changes in estrogen metabolism could be one way physical activity lowers breast cancer risk, according to research published in the journalCancer Epidemiology Biomarkers & Prevention.
Observational studies have found that exercise is associated with a lower risk of breast cancer, but there is little clinical evidence on how exercise might lower breast cancer risk. For this study, 391 sedentary premenopausal women of similar age and body mass index were randomly assigned to one of two groups, a control group and an intervention group. Women in the intervention group did aerobic activity 30 minutes a day five times a week for 16 weeks.
Urine samples were collected at the start and end of the study to measure estrogens and estrogen metabolites. The focus was on changes in two metabolites, 2-hydroxyestrone (2-OHE1) and 16alpha-hydeoxyestrone (16alpha-OHE1). Estrogen metabolism favouring the production of 2-OHE1 is associated with a decreased breast cancer risk.
Researchers found that in the group that did aerobic exercise 2-OHE1 levels increased and 16alpha-OHE1 levels decreased, which led to a significant increase in the 2-OHE1/16alpha-OHE1 ratio. In the control group there was a small, non-significant decrease in this ratio.
The findings suggest that changes in estrogen metabolism may be one way that physical activity lowers the risk of breast cancer.
