Breast Cancer Risk Associated With Sex Hormones Reduced By Losing Weight

The Journal of Clinical Oncology has published a study online which reveals that even a moderate amount of weight loss can considerably decrease levels of circulating estrogens that are linked to a higher risk ofbreast cancer.

Anne McTiernan, M.D., Ph.D., and her team from the Fred Hutchinson Cancer Research Center conducted the first randomized, controlled clinical trial to assess what impact weight loss may have on sex hormones in those with an elevated risk of breast cancer, i.e. overweight and obese postmenopausal women.

McTiernan, who is a director of the Hutchinson Center's Prevention Center and a member of its Public Health Sciences Division declared:

"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."

However, she warns that these results solely apply to women that are overweight or obese who do not take any hormone-replacement therapy.

Epidemiologists have known for quite some time about the association between obesity and a higher risk of postmenopausal breast cancer, and that the relationship between body fat and estrogen production may be a contributing factor.

For their study, the researchers randomized 439 overweight-to-obese, sedentary women from the Seattle area into four different groups. One group was assigned to exercise only, which consisted mainly of brisk walking, whilst the other group was assigned to only a diet. The third group was assigned to exercise plus diet, with the fourth group receiving no intervention. All women were aged between 50 to 75 years. The primary goal of the study was determined as an average weight loss of 10% of their starting weight. In comparison with the exercise only and the no intervention group, both the diet-only and diet-plus-exercise groups met the primary goal.

The researchers measured the impact of diet- and exercise-related weight loss on blood levels of various types of sex hormones, including:

• Estrone
• Estradiol
• Free estradiol
• Total testosterone
• Free testosterone
• A steroid required to produce androstenedione, a sex hormone
• SHBG - a protein that binds to sex hormones making them less biologically active

The researchers note that high levels of SHBG are linked to a decreased risk of breast cancer. Free estradiol and free testosterone are hormone types, which are not bound to SHBG and are therefore more biologically active.

The team discovered that a beneficial impact could be achieved on hormone levels by losing as little as 5% of one's total body weight. The effect was noted to increase with the amount of weight loss.

McTiernan explained: "The amount of weight lost was key to changes in hormone levels. The biggest effect was through diet plus exercise; exercise by itself didn't produce much of a change in weight or estrogen."

She continued stating that exercise offers many significant benefits for those on a weight-loss program, as exercise prevents the loss of muscle and bone mass in addition to maintaining weight long term, adding: "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 that this is the first study, which demonstrates that weight loss through a healthy diet, i.e. by reducing calories and fat and increasing vegetables, fruit and fiber, considerably reduces blood estrogen levels in postmenopausal women. 

She continued: "This shows that it's never too late to make lifestyle changes to reduce your risk for breast cancer."

The study outcome could also prove to be of significance to women who are overweight, who take breast cancer prevention drugs that either block or stop the production of estrogen, like tamoxifen, raloxifene and exemestane.