Weight loss may reduce breast cancer risk

Women approaching menopause should strive to maintain or lose weight.

Issue: September 1, 2006

Women who gained in excess of 55 pounds since they were 18 are more at risk for developing breast cancer postmenopause, researchers wrote in a recently published study.

A. Heather Eliassen, ScD, and colleagues from Channing Laboratory, department of medicine, Brigham and Women’s Hospital and Harvard Medical School, theorized since endogenous hormones are a primary cause of breast cancer, that adiposity following menopause may be a modifiable risk factor for breast cancer.

Researchers conducted a prospective cohort study within the Nurses’ Health Study, comprised of 87,143 postmenopausal women, aged 30 to 55 years, who had been followed between 1976 and 2002. Researchers noted 4,393 cases of invasive breast cancer during that time.

The research team concluded that compared with women who maintained their weight since age 18, those women who gained more than 55 pounds were at an increased risk of breast cancer (RR 1.45; 95% CI, 1.27-1.66) with an even higher risk among women who never took postmenopausal hormones (RR=1.98; 95% CI, 1.55-2.53). Their results were published in the Journal of the American Medical Association.

In a separate analysis, researchers compared women who gained more than 22 lbs since menopause with women who maintained their weight. They concluded they too had an increased risk of breast cancer (RR, 1.18;95% CI, 1.03-1.35).

Less weight, decreased risk

On the other hand, researchers noticed that women who had dropped 22 pounds or more since menopause or who kept the weight off over a long period of time were less likely to develop breast cancer than those who maintained their weight since menopause.

“Higher weight at younger ages decreases breast cancer risk for both premenopausal and postmenopausal women, possibly due to slower pubertal growth or a greater likelihood of irregular menstrual cycles and ovulatory infertility in adulthood,” the researchers wrote. “Although the ovaries produce endogenous hormones in premenopausal women, ovarian hormone production declines after menopause and adipose tissue becomes the primary estrogen source by aromatization of adrenal androgens. Compared with normal weight postmenopausal women, those with higher BMI have two-fold higher circulating estrogens and lower sex hormone-binding globulin levels, and thus more bioavailable estrogens. Weight reduction in postmenopausal women decreases circulating estrogen levels and increases sex hormone-binding globulin levels,” they wrote.

Researchers noted they did not include physical activity as a covariate in the analysis because their primary interest was the change in weight, not how it occurred. Adding physical activity, however, did not alter the results; neither did adding oral contraceptive use.

They said about 15% of cases in these women may have been attributable to weight gain since age 18.

“This study provides more evidence of the benefits of maintaining a healthy weight, and of weight loss in those who are overweight,” Eliassen said. “In addition to the short-term benefits of weight loss, such as improved insulin sensitivity, blood pressure, and cholesterol, we now have evidence of long-term benefits in terms of breast cancer risk reduction.”

Although many risk factors for breast cancer have been identified, most of them are not easy to modify, Eliassen added. “Weight is one of the few risk factors that women can do something about, and our study suggests it is never too late to lose weight to reduce breast cancer risk. However, given how difficult it is to lose weight, the best advice for women would be to maintain a healthy weight and avoid weight gain in the first place,” she said.

This article also appeared in Endocrine Today, a SLACK Incorporated publication.

For more information:

Eliassen AH. Colditz GA, Rosner B, et al. Adult weight change and risk of postmenopausal breast cancer. JAMA. 2006;296:193-201.