Breastfeeding May Train the Body to Fight Breast Cancer, Study Finds

For years, moms have heard that breastfeeding can help lower the risk of breast cancer. But until now, scientists weren’t sure how it actually works. New research published in Nature reveals something extraordinary: breastfeeding may “train” the immune system to protect the body for decades.

Also read: 10 Ways You and Your Baby Can Benefit from Breastfeeding

The study, led by Dr. Sherene Loi of the Peter MacCallum Cancer Centre in Australia, examined breast tissue from 260 women aged 20 to 70. Researchers found that women who had breastfed had higher levels of special immune cells called CD8+ T cells.

Think of these cells as tiny guards that stay in the breast tissue, always on alert for abnormal cells that could develop into cancer. What makes this finding remarkable is that these protective cells can last up to 50 years after breastfeeding. That means the body “remembers” the experience of lactation and keeps those guards in place long after the baby stage.

To explore how this works, the team studied mice that went through pregnancy, breastfeeding, and weaning. The mice that had nursed developed the same protective immune cells. When exposed to aggressive breast cancer cells, tumor growth was slower than in mice that had not nursed. This suggests that breastfeeding itself triggers a long-lasting immune defense.

Previous research has shown that breastfeeding lowers a woman’s breast cancer risk by about 4 percent for every year she nurses. Until now, many experts thought hormones were the main factor. This study points to another mechanism: by creating long-lived immune cells, breastfeeding may leave behind a natural defense system that can identify and respond to abnormal changes in breast tissue.

Professor Loi says this protection may have originally evolved to help mothers fight off infections like mastitis during the early postpartum period. Today, it may also explain why women who breastfeed are less likely to develop aggressive types of breast cancer, such as triple-negative breast cancer.

Her team also found that among women who did develop breast cancer, those who had breastfed had tumors with more protective T cells and in some cases lived longer after diagnosis.

Researchers believe these immune cells form to help the body fight off infection during breastfeeding, but they may also continue to monitor breast tissue later in life. Understanding how this works could one day help experts design new ways to prevent or treat breast cancer, especially for women who can’t or choose not to breastfeed.

At the same time, health experts caution that breastfeeding is not a guarantee against breast cancer. Genetics, age, and hormone exposure all influence individual risk. Breastfeeding is one part of motherhood, and while it offers many benefits, it’s not always possible or the right choice for every family.

Learn how breastfeeding may also lower a mom’s risk of heart disease and stroke here.