Breast Cancer Linked to Weight of Women After Menopause

One in four cases of breast cancer in post-menopausal women who have not used hormone replacement therapy is caused by weight gain, but the risk can be substantially lowered by losing weight, researchers reported today.

Researchers found that if the women lost at least 22 pounds, they could reduce their risk of breast cancer by about 40%. If they managed to keep the weight off for at least four years, the risk was reduced by 60%.

“Weight is one of the few risk factors for breast cancer women can do something about,” said lead author A. Heather Eliassen, an epidemiologist at Brigham and Women’s Hospital and Harvard Medical School in Boston.

The reduction in risk from weight loss means that over five years, if 100,000 overweight women each lost 22 pounds, 515 cases of breast cancer would be avoided. If they kept it off, 793 women would be spared.

Dr. Robert J. Morgan, a medical oncologist at the City of Hope in Duarte who was not involved in the study, said the research was more evidence of how people could “avoid cancer by the way they live.”

The new report, published in the Journal of the American Medical Assn., is the first to look at the effects of losing weight after menopause.

Previous studies have established the connection between fat and breast cancer. Fat tissue produces estrogen, which fuels tumor growth in some kinds of breast cancer.

Other risk factors for breast cancer include a family history of the illness, early onset of menstruation, smoking and alcohol consumption.

The new report, which followed more than 87,000 women for 26 years, documented that gaining weight increased the chance of breast cancer.

Women who gained 55 pounds or more after age 18 increased their breast cancer risk by 45%. Gaining 22 pounds or more after menopause increased the risk of breast cancer by about 20%, the report said.

Among the women who gained 55 pounds or more throughout adulthood, those who did not use hormone replacement therapy increased their breast cancer risk by 98%, while those who did use the therapy increased their risk by 20%.

Eliassen said the use of hormone replacement therapy, which replaces the estrogen women lose during menopause, probably masked the effects of excess fat on breast cancer because estrogen levels were already elevated in those women.

“Although this study ... suggests that it is never too late to lose weight to decrease risk,” Eliassen said, “women should avoid gaining weight both before and after menopause to decrease their post-menopausal breast cancer risk.”