Moderate Weight Loss May Be Way to Lower Breast Cancer Risk For Overweight, Postmenopausal Women

The first randomized, controlled clinical trial testing the effect of weight loss on sex hormone levels in overweight, postmenopausal women shows a benefit with moderate weight loss. According to the study, which was led by Anne McTiernan, MD, PhD of the Fred Hutchinson Cancer Research Center, a positive impact was noted on circulating estrogen in women who lost as little as 5% of their total body weight-estrogen is associated with increased breast cancer risk. The hormone reduction effect increased with further weight loss. The results of the study are published online in the Journal of Clinical Oncology, a publication of the American Society of Clinical Oncology.

A total of 438 overweight or obese, sedentary women between the ages of 50 and 75 were randomly assigned to one of four groups: exercise only, diet only, diet plus exercise, or no change. Those women in the diet-only or diet-plus-exercise study arms decreased their body weight by an average of 10% from their starting weight. McTiernan and colleagues also found significant decreases in sex hormone levels among the women who lost weight-the most significant reductions were in the diet-plus-exercise group.

Of the three forms of estrogen measured in the blood of the subjects, the most dramatic decrease was in levels of free estradiol-levels decreased by 21.4% in the diet-only group and 26% in the diet-plus-exercise group. Free estradiol is the biologically active form of estrogen in the body.

The study also measured two types of testosterone, total and free testosterone and sex hormone binding globulin (SHBG), a protein that binds to sex hormones to make them active. SHBG levels increased by 22.4% in the diet-only group and by 25.8% in the diet-plus-exercise group. Hormones bound by SHBG are generally the inactive forms of sex hormones and higher levels of SHBG are associated with a reduced breast cancer risk according to previous studies.

McTiernan emphasized that as little as a 5% reduction in body weight can cut the risk of estrogen-sensitive breast cancers by as much as 25%. She also cautioned that the study results should not be extrapolated to other groups of women but only apply to overweight or obese women who are not taking hormone-replacement therapy.

The link between postmenopausal breast cancer and obesity has been observed and is thought to be linked to body fat and estrogen production. However, said McTiernan, this is the first study that demonstrates weight reduction by establishing healthy eating habits-reduced caloric intake, higher fiber consumption, and more fruits and vegetables-can lower blood estrogen levels significantly. “This shows that it’s never too late to make lifestyle changes to reduce your risk for breast cancer,” McTiernan added in a statement.

Obesity has been linked with various types of cancer, but studies such as this one are getting to the root of the obesity-cancer link by identifying the mechanisms of how fat tissue can influence cancer development directly. Previous studies have shown that the stage of life when a woman becomes overweight may contribute to breast cancer risk. Weight gain in adulthood (after age 18) and until age 60 is associated with higher breast cancer risk postmenopause, for example. This risk is linked to estrogen. Because the most important postmenopausal source of estrogen is fat tissue, it is thought that the fat tissue of obese and overweight women contributes to development of estrogen-positive breast cancer.

Some women currently take drugs such as tamoxifen, raloxifene, and exemestane to prevent breast cancer. These drugs stop estrogen production or block the activity of circulating estrogen in women particularly at risk for the cancer. Tamoxifen has been used for almost a decade for breast cancer prevention. But these drugs are taken for a maximum of 5 years-tamoxifen side effects include blood clots, strokes, and uterine cancer. Other effects include menopause symptoms. McTiernan believes that weight loss and stable weight through continued exercise is an option to reduce long-term breast cancer risk without significant side effects. Best of all, a healthy diet and exercise are better for quality of life overall, and for the prevention of chronic diseases such as heart disease and diabetes.

“I recommend women both diet and exercise, because in the long run that should help keep weight down and therefore keep estrogens down,” McTiernan said in a statement.