05/22/2012 11:58 am ET

Weight Loss Could Decrease Estrogen, A Known Risk Factor For Breast Cancer: Study

Weight loss might help to decrease a risk factor for breast cancer, according to a new study.

For obese and overweight women, losing just 5 percent of total body weight could help to lower circulating estrogen levels linked with increased breast cancer risk, according to the study in the Journal of Clinical Oncology.

The researchers from the Fred Hutchinson Cancer Research Center conducted their study on 439 women between the ages of 50 and 75, all of whom were overweight or obese. They were split up into four groups: the diet-only group, the exercise-only group (which consisted mainly of walking at a brisk pace), the exercise-and-diet group and the no-intervention group.

Researchers found that the people in the diet-only and the exercise-and-diet group experienced the most weight loss, at 10 percent of their starting weight on average. The women in these two groups also experienced the greatest drop in hormones linked with breast cancer.

For example, estrone levels -- a kind of estrogen -- decreased 9.6 percent in women who dieted, and 11.1 percent in women who dieted and exercised. Levels of estradiol -- another kind of estrogen -- dropped 16.2 percent in women who dieted and 20.3 percent in women who dieted and exercised.

In addition, levels of sex hormone binding globulin (SHBG) were increased by 22.4 percent in women who dieted and 25.8 percent in women who dieted and exercised. High levels of SHBG are linked with lower breast cancer risk.

"The biggest effect was through diet plus exercise; exercise by itself didn't produce much of a change in weight or estrogen," study researcher Anne McTiernan, M.D., Ph.D., said in a statement.

Researchers noted that there's a generally known link between obesity and breast cancer in postmenopausal women, with body fat and the production of estrogen playing a role.

Therefore, "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," McTiernan said in the statement.

Last year, a study in the European Journal of Cancer Prevention showed that regular exercise could cut a woman's risk of dying from breast cancer by almost 40 percent. That study included 1,508 women who were tracked for five years.