When it comes to breast cancer, we are often alarmed by risk factors, such as family history and environmental toxins, over which we have no control. So it’s refreshing to know that there are things we women CAN do to reduce our risk of this all-too-common and dreaded disease. And now, thanks to results of a first-of-its-kind scientific study*, we know that maintaining a healthy weight—something we can control—can reduce our risk of getting this disease.

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.

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), modified diet only, exercise plus modified 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.

Because hormones havelong been implicated in many types of breast cancer, the researcher looked at 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).

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.

Dr. McTieran points out that this data applies only to overweight and obese women. However, it provides strong incentive for all post-menopausal women to maintain a healthy Body Mass Index (BMI) to help prevent breast cancer.