Breastfeeding and reduced breast cancer risk

A major benefit of breastfeeding is a decrease in the risk of developing breast cancer.

Breastfeeding is important for the health of both infant and mother. One benefit of breastfeeding for the mother is a decrease in the risk of developing breast cancer. Breast cancer is the second most common cancer in the world, and the most common cancer in women. It is clear that the most important factors in a woman’s risk of breast cancer are age and family history. After these factors are taken into account, breast cancer is still more common in women who have not breastfed, compared to women who have breastfed, but the extent of the benefit is not clear.

When results of studies are combined together, researchers have shown there is a 4.3 percent decrease in the risk of breast cancer for each year of breastfeeding, regardless of where the woman lives, age, menopausal status and family history. Another study that combined previous studies showed that there was a reduction in breast cancer risk only for those who had breastfed for at least one year. A 2010 study in Brazil found that those who breastfed for at least one year had a 66.3 percent reduction in the risk of developing breast cancer, those who breastfed at least two years had a 87.4 percent reduction in risk, and those who breastfed at least three years had a 94 percent reduction in risk.

The differences in results may have to do with the types of breast cancers that are affected by breastfeeding. Researchers have found that breastfeeding is the most protective against aggressive forms of breast cancer such as triple-negative, basal-like and BRCA 1 mutation-associated breast cancers. For example, women who are carriers of the BRCA 1 mutation and breastfeed for at least one year have a 32 percent reduced risk of cancer compared to women with the mutation who do not breastfeed for at least one year. Though we don’t know the exact reasons breastfeeding decreases the risk of breast cancer, it seems that the benefits are due to changes in breast tissue and decreased number of lifetime menstrual cycles seen with pregnancy and breastfeeding.

If you have questions related to breastfeeding and the risk of developing breast cancer, contact the Michigan State University Extension office in your area or find a Breastfeeding Peer Counselor through the Breastfeeding Initiative website.

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