20 Months Total Breast-Feeding May Lower A Woman's Risk Of Developing Breast Cancer

December 02, 1997

BUFFALO, N.Y. -- Breast-feeding for at least 20 months during their lifetime appears to offer women some protection against developing breast cancer later in life, a study by epidemiologists at the University at Buffalo has found.

Results of their case-control study involving 1,313 women showed that premenopausal women had a 50 percent lower risk of breast cancer if they had breast-fed for at least 20 months, compared to women who had at least one baby and had not breast-fed. There was no effect of breast-feeding on the risk of breast cancer for women who were postmenopausal at the time of the study.

The study is published in the Dec. 2 issue of the American Journal of Epidemiology, which is dedicated to research by faculty members and graduates of the UB Department of Social and Preventive Medicine.

"This is one of a number of studies now that show a decreased risk of breast cancer with breast-feeding," said Jo L. Freudenheim, Ph.D., UB associate professor of social and preventive medicine and primary researcher on the study.

"There is some question, however, about whether this is related to how long a woman breast-feeds, to inherent breast problems in women who don't succeed in breast-feeding when they try, to treatments to stop milk production or just to cessation of menstruation.

"This study shows that breast-feeding is protective, but the effect appears only if women breast-feed over a longer period of time," Freudenheim said. Breast-feeding time was measured in cumulative months during a lifetime.

UB researchers analyzed health history and breast-cancer risk factors of 250 premenopausal women and 367 postmenopausal women who had been diagnosed with primary breast cancer between 1986 and 1991, along with data from 693 cancer-free women who served as a control group. All women had at least one live birth, and cases and controls were matched by age.

The women were interviewed in person about a number of potential breast-cancer risk factors, including whether they had breast-fed their infants, how long they breast-fed, why they

had stopped and whether those who did not breast-feed had received medication to stop milk flow.

Adjusting for other breast-cancer risk factors, the researchers found that breast-feeding appeared to provide a decrease in risk, but only for premenopausal women who had breast-fed for at least 20 months.

Freudenheim said one explanation for this finding may be the possibility that earlier pregnancy and breast-feeding may cause breast tissue to go through a development phase that makes it less susceptible to carcinogens. Conversely, late first pregnancy long has been considered a risk factor for developing breast cancer.

There was no indication that women who stopped breast-feeding because of insufficient milk supply, or who had received treatment to stop milk flow, were at increased risk, Freudenheim said.

Additional researchers on the study were Saxon Graham, Ph.D.; John Vena, Ph.D.; Kirsten Moysich, Ph.D.; Paola Muti, Ph.D., and Rosemary Laughlin, Ph.D., all from the UB Department of Social and Preventive Medicine; Takuma Nemoto, M.D., from the UB Department of Surgery, and James Marshall, Ph.D., formerly of the UB Department of Social and Preventive Medicine, now at the Arizona Cancer Center.
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University at Buffalo

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