Physical activity reduces the risk of developing breast cancer because it changes the way the hormone oestrogen is broken down, according to a new study.
The research, carried out by the University of Minnesota’s Department of Food Science, found that women who exercise regularly produced different oestrogen waste products to women who led a sedentary lifestyle.
Professor Mindy Kurzer, who led the study said: ‘Studies suggest physical activity lowers breast cancer risk, but there are no clinical studies that explain [why].
‘Ours is the first study to show that aerobic exercise influences the way our bodies break down oestrogens to produce more of the ‘good’ [byproducts] that lower breast cancer risk.’
The Women in Steady Exercise Research (WISER) clinical trial, involved 391 sedentary, healthy, young, premenopausal women.
They randomly assigned the women to two age-matched, body mass index-matched groups: a control group of 179 women and an intervention group of 212 women.
While women in the control group continued a sedentary lifestyle for the entire study period, women in the intervention group performed 30 minutes of moderate-to-vigorous exercise five times a week for 16 weeks.
Aerobic exercises included the treadmill, stair stepper or elliptical machine.
The researchers adjusted the workout intensity for each individual so that the maximal heart rate was uniform among all participants.
The researchers collected daily urine samples on three days prior to study and on three consecutive days at the end of the study.
They then measured the levels of three types of oestrogen and nine of their by-products or metabolites, in the participants’ urine samples.
The results showed that those who exercised produced more of by-product called 2-OHE1 and less of another called 16alpha-OHE1, which has been linked with a reduction in breast cancer risk.
There were no changes in the levels of these chemicals in those who did not exercise.
‘Exercise, known to favour fitness and improve heart health, is also likely to help prevent breast cancer by altering estrogen metabolism,’ said Kurzer.
‘It is very important, however, to decipher the biological mechanisms behind this phenomenon.’
In collaboration with researchers at the University of Pennsylvania in Philadelphia, Professor Kurzer is now conducting similar studies in women with a high risk for breast cancer.
The research was published in Cancer Epidemiology, Biomarkers & Prevention, a journal of the American Association for Cancer Research..