By William J. Cromie

Gazette Staff

One way for postmenopausal women to avoid breast cancer is to stay slim, say researchers at the School of Public Health. This is especially true for those who don't take hormone replacement pills.

One out of six postmenopausal women may prevent breast cancer by not gaining more than 15 to 20 pounds above her weight at age 18. Not doing so can double a women's risk for the dread disease.

Postmenopausal women who don't take estrogen pills and gain 22 to 44 pounds after age 18 increase their chances of getting breast cancer by 61 percent, reports Zhiping Huang, a research fellow in nutrition. Those who add more than 44 pounds double their risk compared to women who keep their weight down.

Worse still, heavy women, in both their pre- and post-menopausal years, increase their chances of dying from the disease. Obese women are twice as likely to die from breast cancer as those who gain little weight in their adult years.

Surprisingly, however, the study found that overweight women in the years before menopause actually have a reduced risk of getting the disease in the first place. The reason revolves around estrogen, a hormone that raises the risk of the disease for all women.

"Before menopause, ovaries produce a large amount of estrogen, while the contribution from fat is negligible," explains Meir Stampfer, professor of epidemiology and nutrition. "What's more, fat also impairs the working of the ovaries. That impairment probably accounts for reduced estrogen and the lower risk of breast cancer that heavy women enjoy."

After menopause, taking pills containing estrogen raises the risk of breast cancer more than being overweight. "When postmenopausal women use hormone replacement therapy to reduce their risk of heart disease and osteoporosis, the additional estrogen far outweighs that produced by fat," notes JoAnn Manson, associate professor of medicine.

"The most important message from our study," Manson says, "is to avoid substantial weight gain after age 18. Although weight provides some protection from breast cancer in premenopausal years, it increases the risk of heart disease, diabetes, and certain cancers."

The good news is that weight gain and hormone use can be controlled by most women. Such control could reduce the estimated 34 percent of postmenopausal breast cancer cases caused by hormone replacement therapy, weight gain, or a combination of both.

These findings come from the Nurses' Health Study, which has followed more than 92,000 nurses for 16 years. During that time 1,000 premenopausal and 1,517 postmenopausal women were diagnosed with invasive breast cancer. The National Cancer Institute estimates that a total of 180,000 new cases of the disease will occur in the United States this year. About 44,000 women are expected to die from it.

The Harvard scientists describe their research in Wednesday's issue of the Journal of the American Medical Association. Co-authors of the report include researchers from the Medical School and Brigham and Women's Hospital.

An editorial in the same issue of the journal notes that this study "provides perhaps the strongest evidence to date that weight gain from early adulthood is an important cause of postmenopausal breast cancer."

It also notes that the research raises several unanswered questions. These include whether specific times exist when weight gain is most likely to increase breast cancer risk, and whether deliberate weight loss can reverse the effects of weight gain.