Weight gain, particularly after menopause, is associated with an increased risk of breast cancer in women, according to an article in the July 12 issue of JAMA.

Background information in the article indicates that weight loss after menopause lowers circulating estrogen hormones in women, and because estrogen is directly related to breast cancer, weight loss is thought to decrease risk of the disease. Studies show that weight gain since early adulthood is associated with increased breast cancer risk in postmenopausal women, particularly those not taking postmenopausal hormones. However, weight changes in middle-aged to older women (50 years and older) has been studied less extensively.

A. Heather Eliassen, Sc.D., of Brigham and Women’s Hospital and Harvard Medical School, Boston, and colleagues analyzed data within the Nurses’ Health Study to determine the association between weight change and the risk of breast cancer among postmenopausal women.

The researchers assessed weight change for two different periods - since 18 years of age and since menopause. A total of 87,143 postmenopausal women (ages 30 to 55 years) were followed up for up to 26 years to analyze weight change since age 18. Weight change since menopause was assessed among 49,514 women (followed up for up to 24 years).

Women who gained about 55 pounds or more since age 18 were at a 45 percent increased risk of breast cancer, compared with those who maintained their weight, with a stronger association among women who have never taken postmenopausal hormones. Women who gained about 22 pounds or more since menopause were at an 18 percent increased risk of breast cancer. Those who lost about 22 pounds or more since menopause (and kept the weight off) and had never used postmenopausal hormones were at a 57 percent lower risk of breast cancer than those who simply maintained their weight. The researchers concluded that 15 percent of the study’s breast cancer cases may be attributable to weight gain of 4.4 pounds or more since age 18 and 4.4 percent of the cases may be attributable to weight gain of 4.4 pounds or more since menopause.

“These data suggest that weight gain during adult life, specifically since menopause, increases the risk of breast cancer among postmenopausal women, whereas weight loss after menopause is associated with a decreased risk of breast cancer,” the authors write. “Women should be advised to avoid weight gain both before and after menopause to decrease their postmenopausal breast cancer risk.

American Medical Association (AMA)