Many studies have shown a link between exercise and a lower risk of breast cancer, but the reason why hasn’t been clear. Now new research is starting to provide an answer by showing that aerobic exercise seems to change how our bodies break down estrogen. It’s the first study to show that aerobic exercise has a direct impact on estrogen metabolism in premenopausal women.
The study was published in the May 2013 issue of the journal Cancer Epidemiology, Biomarkers & Prevention. Read the abstract of “The Effects of Aerobic Exercise on Estrogen Metabolism in Healthy Premenopausal Women.”
The researchers wanted to find out whether exercise affects the body’s production of compounds produced when estrogen is broken down. These compounds are called estrogen metabolites. Earlier research has suggested that a higher ratio of certain “good” estrogen metabolites to certain “bad” estrogen metabolites was linked to lower breast cancer risk. The “good” metabolite is called 2-hydroxyestrone (2-OHE1) and the “bad” metabolite is called 16alpha-hydroxyestrone (16alpha-OHE1). 2-OHE1 can reduce the effects of estradiol, a type of estrogen that’s been linked to breast cancer development. 16alpha-OHE1 can contribute to cell processes that could lead to the development of breast cancer.
The researchers randomly assigned 391 inactive, healthy, young, premenopausal women to either a non-exercising control group or an exercise intervention group. The women were between 18 and 30 years old and ranged in weight from healthy to obese.
The women in the control group continued an inactive lifestyle for the 16-week study period. The women in the intervention group did 30 minutes of moderate-to-vigorous aerobic exercise five times a week during the 16 weeks. The intensity of the workouts was adjusted for each woman so they all had similar maximum heart rates.
For 3 days before the study started and 3 days after it ended, the researchers measured the amount of certain estrogen metabolites in the women’s urine.
At the end of the study, the women in the exercise group had higher levels of 2-OHE1 (“good” estrogen metabolites) and lower levels of 16alpha-OHE1 (“bad” estrogen metabolites). This means the ratio of 2-OHE1 to 16alpha-OHE1 was higher in women who exercised. This ratio increase didn’t happen in women in the inactive group.
There were no other differences in other estrogen metabolites or ratios in either group.
Over the course of the study, the women in the exercise group also became more aerobically fit, gained more lean body mass, and lost body fat.
Based on the results, the researchers concluded that the effect exercise has on estrogen metabolism may be one explanation of how exercise reduces breast cancer risk.
Keep in mind that we don’t know the exact ideal amount or intensity of exercise to reduce breast cancer risk. The American Cancer Society and many doctors recommend that women who’ve been diagnosed with breast cancer exercise regularly -- about 4 to 5 hours per week at a moderate intensity level.
Along with healthy diet and lifestyle choices, regularly doing moderately intense exercise is one the best steps all women can take to help keep breast cancer risk as low as it can be. Regular exercise also helps keep your general health the best that it can be. No matter how old you are, it's never too soon or too late to get moving.
Visit the Breastcancer.org Exercise pages for tips on exercising safely and how to stick to an exercise routine.