Breast-Feeding For At Least 12 Months During Their Lifetime Lowers Women's Risk of Breast Cancer, UB Study Finds

BOSTON -- Breast-feeding for at least 12 months during their lifetime appears to offer women some protection against developing breast cancer later in life, a new study by epidemiologists at the University at Buffalo has found.

Results of their case-control study involving 1,280 women showed that premenopausal women had a 29 percent lower risk and postmenopausal women a 24 percent lower risk of breast cancer if they had breast-fed for at least 12 months, compared to women who had at least one baby and did not breast-feed.

Jo L. Freudenheim, Ph.D., UB associate professor of social and preventive medicine, presented the study results here today (June 13) at the annual meeting of the Society for Epidemiologic Research. An earlier study by Freudenheim showed that women who were breast-fed as infants had a lower risk of getting breast cancer than women who were bottle-fed.

"There is fairly consistent evidence in the scientific literature of a decreased risk of cancer with breast-feeding," Freudenheim said. "But there is some question about whether this is related to how long a woman breast-feeds, to inherent breast problems in women who donÍt succeed in breast-feeding when they try, to treatments to stop milk production, or just to cessation of menstruation."

UB researchers sought to shed light on these issues by comparing health history and breast-cancer risk factors of 587 women who had been diagnosed with primary breast cancer between 1986 and 1991, 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. Among postmenopausal women, the positive effect was found only for those who first breast-fed before age 25.

Freudenheim said one possible explanation for this finding is the idea that earlier pregnancy and breast-feeding may cause breast tissue to go through a final development phase, making it less susceptible to other 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, from the UB Department of Social and Preventive Medicine, were Saxon Graham, James Marshall, John Vena, Kirsten Moysich, Paola Muti and Rosemary Laughlin, as well as Takuma Nemoto from the UB Department of Surgery.