Taking part in a physical activity program lowers the concentration of sex hormones only in women who are losing body fat. This has been reported by researchers from University Medical Center (UMC) Utrecht and the National Institute for Public Health and the Environment (RIVM) in their paper published on July 6, 2009 in the Journal of Clinical Oncology. A high concentration of sex hormones in postmenopausal women increases the risk of breast cancer.
Doctor Evelyn Monninkhof from the Julius Center for Health Sciences and Primary Care at UMC Utrecht, who is leading this research together with the RIVM, has studied nearly two hundred women from the area of Utrecht. Half of the women followed a 1-year physical exercise program at a professional gym and the other half were asked to carry on with their normal exercise pattern. The program consisted of aerobics and spinning combined with muscle strength training which was supplemented by walking and cycling. All of the women were postmenopausal and were between the ages of 50 and 69 years.
Monninkhof compared the concentrations of sex hormones before, during and after the study. Results showed that following the physical exercise program had no effect on the hormone levels of all of the women in the exercise group. After one year, the women who had taken part in the exercise program did not have lower hormone levels than the women in the control group and therefore did not have a lower risk of breast cancer.
However, Monninkhof did see an effect of the physical exercise program in women who had lost weight. In women where the amount of body fat had decresed by more than two percent, the concentrations of sex hormones were lower in the exercise group than in the control group. In addition, the study showed that hormone levels dropped in all of the women who had lost weight. Loss of body fat is, incidentally, not the same as weight loss in general.
Worldwide, this study is only the second time that scientists have studied the effect of a physical activity program on sex hormone levels. Women who undertake physical exercise regularly, are estimated to have a twenty to forty percent less risk of contracting breast cancer than women who only do limited physical exercise. Overweight in postmenopausal women is in itself a risk factor. Sex hormones are thought to be the most likely link between exercise, overweight and risk of breast cancer. The question remains whether exercise itself works because it induces weight loss in women or because the exercise has an effect on the risk of breast cancer. Breast cancer is the most commonly occurring type of cancer in women – one in nine women will get this disease.
The Dutch Cancer Society (KWF) has contributed to funding for this research. Researchers from the Julius Center of UMC Utrecht collaborated with the RIVM for this study.