Study finds moderate weight loss reduces levels of sex hormones linked to breast cancer risk

Even a moderate amount of weight loss can significantly reduce levels of circulating estrogens that are associated with an increased risk of breast cancer, according to a study by researchers at Fred Hutchinson Cancer Research Center – the first randomized, controlled clinical trial to test the effects of weight loss on sex hormones in overweight and obese postmenopausal women, a group at elevated risk for breast cancer.

The findings by Anne McTiernan, M.D., Ph.D., and colleagues are published online ahead of the May 21 issue of the Journal of Clinical Oncology, a publication of the American Society of Clinical Oncology.

"Based on previous research, our results suggest that losing just 5 percent or more of one's weight could cut by a quarter to a half the risk for the most common, estrogen-sensitive breast cancers," said McTiernan, director of the Hutchinson Center's Prevention Center and a member of its Public Health Sciences Division. McTiernan cautions that these findings only apply to overweight or obese women who are not taking hormone-replacement therapy.

Epidemiologists have long noted a link between obesity and increased risk of postmenopausal breast cancer. A relationship between body fat and estrogen production is thought to contribute to this risk.

The study was based on data from 439 overweight-to-obese, sedentary, Seattle-area women, ages 50 to 75, who were randomly assigned to one of four groups: exercise only (mainly brisk walking), diet only, exercise plus diet and no intervention. At the end of the study, participants on the diet-only and diet-plus-exercise arms lost an average of 10 percent of their starting weight, which was the goal of the intervention.

The study measured the effects of diet- and exercise-related weight loss on blood levels of several types of sex hormones, including three forms of estrogen (estrone, estradiol and free estradiol); two types of testosterone (total testosterone and free testosterone); a steroid necessary for the production of sex hormones (androstenedione) and sex hormone binding globulin, or SHBG, a protein that binds to sex hormones and therefore makes them less biologically active. High levels of SHBG are associated with reduced breast cancer risk. Free estradiol and free testosterone are forms of the hormones that are not bound to SHBG and therefore are more biologically active.

At the end of the study, the researchers found significant reductions in hormone levels among the women who received the dietary weight loss intervention, with the most striking results among those who both dieted and exercised:

- Estrone levels decreased 9.6 percent with diet and 11.1 percent with diet plus exercise.
- Estradiol levels decreased 16.2 percent with diet and 20.3 percent with diet plus exercise.
- Free-estradiol levels decreased 21.4 percent with diet and 26 percent with diet plus exercise.The researchers found that losing as little as 5 percent of one's total body weight had a beneficial impact on hormone levels, and the effect increased with the amount of weight lost.