Losing weight—even just a moderate amount—can significantly reduce the levels of circulating estrogen in the body, thereby reducing the risk of breast cancer, according to the results of a study published in the Journal of Clinical Oncology.
Breast cancer is the most commonly diagnosed type of cancer (other than skin cancer) in U.S. women. Each year, roughly 227,000 women are diagnosed with breast cancer and close to 40,000 die of the disease.
There are a number of risk factors associated with breast cancer, including obesity, overweight, increased levels of circulating estrogen, and a sedentary lifestyle. Some breast cancers are stimulated to grow by the female hormone estrogen. What’s more—estrogen levels have been shown to be elevated in obese individuals and this could lead to an increased risk of postmenopausal breast cancer.
Researchers at the Fred Hutchinson Cancer Research Center performed the first randomized, controlled clinical trial to evaluate the effects of weight loss on sex hormones in overweight and obese postmenopausal women. The study included data from 439 overweight-to-obese, sedentary women ages 50 to 75 from the Seattle area. The women were randomly assigned to one of four groups: exercise only, diet only, exercise plus diet, or no intervention. At the end of the study period, the women in the diet only and diet plus exercise groups lost an average of 10 percent of their starting weight.
The researchers then measured the effects of this weight loss on the blood levels of several types of sex hormones, including three forms of estrogen; two types of testosterone; androstenedione, a steroid necessary for the production of sex hormones; and sex hormone binding globulin, or SHBG, a protein that binds to sex hormones and therefore makes them less biologically active.
At the end of the study, the researchers found significant reductions in hormone levels among women who lost weight, with the biggest reduction among those who were in the diet plus exercise group.
High levels of SHBG are associated with reduced breast cancer risk, whereas high levels of estrogen (estrone, estradiol, and free-estradiol) are associated with an increased risk. In the diet plus exercise group, estrone levels decreased 11.1%, estradiol levels decreased 20.3%, free estradiol levels decreased 26%, and SHGBF levels increased 25.8%. In the diet only group, estrone levels decreased 9.6%, estradiol levels decreased 16.2%, free estradiol levels decreased 21.4%, and SHGBF levels increased 22.4%.
The amount of weight lost impacted the changes in hormone levels. Losing as little as 5% of one’s total body weight had a beneficial impact on hormone levels, and the effect increased with the amount of weight lost. The biggest effect was seen in the diet plus exercise group.
This is the first study to show that losing weight through a healthy diet and exercise program significantly lowers blood estrogen levels in postmenopausal women. It provides evidence that lifestyle changes do have an impact on breast cancer risk—even the smallest changes can make a big difference.
Campbell KL, Foster-Schubert KE, Alfano CM, et al. Reduced-calorie dietary weight loss, exercise, and sex hormones in postmenopausal women: Randomized controlled trial. Journal of Clinical Oncology. Published early online May 21, 2012. doi: 10.1200/JCO.2011.37.9792
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