Some breast cancers seem to be related to a genetic tendency for cells in some women’s breasts to mutate and grow at an out-of-control rate. Another type stems from a normally occurring gene designed to help breast cells grow, divide and repair themselves, which seems to stimulate cancer cell growth as well.
Even though we are discovering there are many types of breast cancer and many theories of where the cancer comes from, the fact is “breastfeed your baby” is now published as one of the top ten ways to prevent breast cancer.
Most, but not all studies of breastfeeding and breast cancer show a correlation between breastfeeding and a lower risk of breast cancer. While some highlight this correlation more for post-menopausal breast cancer, others demonstrate the reduction of breast cancer in young, pre-menopausal women as well.
One significant study showed a 50% reduction breast cancer rates for premenopausal women who were at higher risk because they have close female relatives with breast cancer. That reduced the risk for those particularly vulnerable women to the same level as other women of the same age who did not have a family history of the disease.
There are a couple of theories about why breastfeeding is protective for women. The most commonly discussed is based on the observation that estrogen fuels 80% of breast cancers. While breastfeeding, a woman’s estrogen level is low. Therefore her lifetime estrogen exposure goes down with each additional month of breastfeeding.
Most studies support this dose related aspect of reducing a woman’s risk of breast cancer. For instance, a study of Chinese women whose lifetime breastfeeding duration averaged 6 years showed a reduction in breast cancer of over 60%. Statistics published in the UK showed mothers reduce their risk of breast cancer by 4.3% for every 12 months of breastfeeding. The monthly duration of breastfeeding is cumulative over a woman’s lifetime, i.e. child #1 + child #2, etc.
Consider prevention from another angle: a woman breastfeeding her daughter has a protective effect on her daughter’s risk for breast cancer too. The daughter’s risk is lowered by a whopping 26-31%.
Most women breastfeed because they know it is the best for their baby. Many may not even realize the benefits for their own health. The preventive effects of breastfeeding work both ways, for mom and for her baby.
References: webpages US Food and Drug Administration, American Cancer Society, World Cancer Research Fund Cancer Prevention Blog, findingDulcinea, National Cancer Institute, Kellymom, Wiklipedia
Freudenheim, J. “Exposure to breast milk in infancy and the risk of breast cancer.” Epidemiology 1994 5:324-331.
USDHHS, Agency for Healthcare Research and Quality, Evidence Report/Technology Assessment #153, Breastfeeding and Maternal and Infant Health Outcomes in Developed Countries, 4/2007.