Breast-Feeding May Protect At-Risk Women From Breast Cancer


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By Anne Harding

MONDAY, Aug. 10, 2009 ( — Women with a family history of breast cancer may have a new weapon against the disease: breast-feeding. In a new study of more than 60,000 women, nursing a baby for at least three months cut the risk of breast cancer in half for those who had a family history of the disease.

The researchers say that breast-feeding could be the equivalent of taking the drug tamoxifen for five years, which is a well-known way to cut breast cancer risk in women with a family history of the disease.

"For women at high risk right now, the things we have to offer are tamoxifen, prophylactic mastectomy—that's about it," says Alison M. Stuebe, MD, of the University of North Carolina at Chapel Hill, who conducted the research while at Brigham and Women's Hospital in Boston. "This study is really good news for women with a family history of breast cancer who are looking to reduce their risk." The study was published Monday in Archives of Internal Medicine.

Some research has suggested that breast-feeding protects against cancer, but those are typically studies in which breast cancer patients and healthy women are asked to recall their behavior years or even decades in the past, Dr. Stuebe notes. These types of studies can be flawed due to "recall bias"—meaning that they rely on people’s sometimes faulty memory, she explains.

In the current study, Dr. Stuebe and her team avoided recall bias by following 60,075 women in the Nurses' Health Study II over the course of nine years. In 1997, the women filled out a questionnaire about whether they had breast-fed each of their first four children, for how long, and whether they had used any lactation-suppressing medications. The researchers then followed them until 2005, during which time 608 were diagnosed with breast cancer.

Overall, the researchers found, women who had ever breast-fed had a 25% lower risk of premenopausal breast cancer. As long as they had nursed at least one of their babies for up to three months, the duration of breast-feeding didn't seem to affect their risk. Whether they had exclusively breast-fed and whether they stopped menstruating during lactation also didn't affect their risk.

Researchers found that breast-feeding didn't affect risk for women who didn't have breast cancer in their family. But for women with at least one close relative with breast cancer—a sister, mother, or daughter—nursing cut the risk of premenopausal cancer by 59% compared to those who didn’t breast-feed. By comparison, women who take tamoxifen or similar drugs for five years, which is recommended for those at particularly high risk of breast cancer, reduce their likelihood of developing breast cancer by 50%.

Women who had used drugs for suppressing lactation were also at lower risk, the researchers discovered. This may be because these women didn't undergo the changes in breast tissue that occur when a woman begins lactating but doesn't actually nurse a child, Dr. Stuebe says. However, women who don't want to breast-feed should not take these drugs based on this study, she adds, because the medications carry many other risks, including the potential for serious blood clots.

Instead, she says, the findings should encourage moms at risk of breast cancer to breast-feed their infants—not that it's always easy, Dr. Stuebe adds.

Hospitals and workplaces need to do a better job of helping women to start nursing their babies and keep at it, she says. A 2009 Centers for Disease Control and Prevention report gave 2,700 U.S. maternity hospitals and birth centers a dismal 63 out of 100, on average, for their policies supporting breast-feeding. Unsupportive practices included giving newborns bottles or handing out free formula samples in gift packs to new moms. Supportive practices included keeping mother and baby in the same room and giving new moms breast-feeding tips.

Going back to work is a huge hurdle to breast-feeding, Dr. Stuebe adds, with many workplaces doing little to help mothers pump on the job. "If you’re a mom and you want to breast-feed, you're troubleshooting and solving problems on a daily basis in order to make that work," she explains.

Julia Smith, MD, the director of the Lynne Cohen High Risk Women's Clinic at New York University, says the study is “very interesting,” but not the final word on breast-feeding and breast cancer. “I think it’s extremely hard to tease out this particular single variable, in that there are still confounding factors that weren’t able to be isolated,” says Dr. Smith. “We can’t be sure it’s really the breast-feeding in that quantity that reduces the risk.”

She notes that 87% of the women in the study breast-fed their infants, a much higher percentage than women in the general population, and that the women who breast-fed tended to be thinner than women who did not. The drop in breast cancer risk may have been due to other lifestyle factors rather than just breast-feeding alone, she says.

“We know there are reasons to breast-feed; on the other hand, I don’t think we really have at this point conclusive evidence that it reduces one's risk of breast cancer significantly in and of itself,” says Dr. Smith, who is also the director of the NYU Cancer Institute's breast cancer screening and prevention program. “I wouldn’t look to this study and say I have to change my priorities and my lifestyle. With all things being equal and you can breast-feed, fine—but a lot of women can’t just sort of change or upend their life for that and I don’t think this study tells us you have to.”