Breastfeeding Reduces Breast Cancer Risk

Breastfeeding and Breast Cancer Risk

A new study finds that breastfeeding significantly reduces the incidence of breast cancer among premenopausal women who have a family history of breast cancer, a factor that places them at especially high risk for the disease.

According to the American Cancer Society, women who have one first-degree relative (mother, daughter, sister) with breast cancer have about a twofold increased risk of getting the disease. The increased risk rises to fivefold for women who have two first-degree relatives with breast cancer.

This latest study, which appeared in the August 10/24 issue of the Archives of Internal Medicine, is not the first to show that breastfeeding is associated with a reduced incidence of breast cancer. It is believed to be the first, however, to show a significant lower risk - 59 percent--of breast cancer in premenopausal women who have an immediate relative who had the disease.

The study evaluated information from 60,075 women who had participated in the second Harvard Nurses’ Health Study. Dr. Alison M. Stuebe, an assistant professor of obstetrics and gynecology at the University of North Carolina and first author of the study, called the results “an impressive reduction in risk” and suggested that breastfeeding may turn out to be as effective a preventive strategy as the use of tamoxifen is for high-risk women.


Tamoxifen, which has been used for about thirty years to treat breast cancer and for about ten years as a preventive approach for women at high risk, is associated with several serious side effects, including blood clots, stroke, uterine cancer, and cataracts. Less serious but common side effects include hot flashes, vaginal discharge, headache, fatigue, nausea, rash, and vomiting.

Approximately 75 percent of new mothers breastfeed at least for a short time during the first six months after giving birth. The American Academy of Pediatrics urges women to breastfeed exclusively for the first six months and to continue breastfeeding for at least the next six months with the additional of supplemental food.

For women, breastfeeding has been associated with a reduced risk of developing ovarian cancer, osteoporosis, high blood pressure, and heart disease. Breastfed infants generally have a lower risk of developing common infant problems, including diarrhea, bacterial meningitis, and ear infections.

The study’s researchers noted several curious findings from the study. One was that the reduction in breast cancer risk did not change among women who had breast-fed exclusively or for longer periods of time. Another was that women who took drugs to prevent milk formation had a lower risk for breast cancer than those who did not breastfeed and who did not take lactation-suppressive drugs. Clearly there are many unanswered questions about the association between breastfeeding and breast cancer risk, and further research is needed.

American Cancer Society
New York Times 8/10/09
Stuebe AM et al. Arch Intern Med 2009; 169(15): 1364-71.