A study in the UNC-Chapel Hill School of Medicine found that women who have a family history of breast cancer are 59 percent less likely to develop the illness if they breastfeed their babies. The study is the first to link breast cancer risk-reduction and breastfeeding to women who have a family history of the disease.

Alison Stuebe, lead author of study, says she compared women who had breastfed to women who had never breastfed to find out whether the first group had a lower risk of getting breast cancer. The study did not show a difference in risk among women who didn’t have a family history of breast cancer.

Stuebe and her colleagues analyzed data from a long-term study of more than sixty thousand women who were pregnant at least once by 1997 and did not have breast cancer at the time. The women were separated into three main groups: those who had breastfed, those who had never breastfed, and those who had never breastfed but used medications to suppress milk production. The authors found that women who breastfed and women who used medications had a lower risk of cancer than women who neither breastfed nor used the suppressive drugs.

“Theories suggest that using the breast and expressing milk makes breast tissue more resistant to cancer,” Stuebe says. “We speculated that maybe there’s something about getting really engorged in the postpartum period that’s problematic. If you block the breast’s engorgement by breastfeeding or taking medication, it appears to provide long-term protection.”

Taking medication to block milk production is not recommended, Stuebe says, since medication can cause blood clots and other life-threatening side effects, including stroke and heart attack.

Another theory proposes that women who are more susceptible to breast cancer have trouble breastfeeding because there is something wrong with their breasts in the first place. But Stuebe says the data don’t support that theory — there was no increased risk among women who breastfed for less than a month. The data also indicated that longer duration of breastfeeding was not more protective.

Stuebe says her group’s findings add to the long list of reasons to breastfeed. It reduces the risk of infectious diseases in babies and decreases risks of heart attack, diabetes, and certain cancers in mothers. Breastfeeding also promotes the release of the “love” hormone oxytocin and helps mothers to bond with their babies.

Despite the benefits of breastfeeding, Stuebe says, the number of women who are able to breastfeed and actually do so is not as high as it should be. “The list of reasons a women cannot physically breastfeed is very short,” she says. “The problem is that women are not getting the resources and support they need.”