11/09/2025
New research reveals a hidden way breastfeeding may protect moms for decades
It’s a discovery that deepens what we know about the lasting strength of maternal biology.
By Himanshi Bahuguna
Updated Oct. 23, 2025
For years, mothers have heard that breastfeeding can lower the risk of breast cancer—but until recently, scientists didn’t fully understand how. Now, new research is revealing an extraordinary layer of protection: breastfeeding may actually “train” the body to guard itself for decades.
The findings, published in Nature, by researchers at the Peter MacCallum Cancer Centre in Australia, suggest that the immune system activates a long-term defense response in the breast during lactation—one that may last well beyond the early years of motherhood. It’s a discovery that deepens what we know about the lasting strength of maternal biology.
Researchers found long-lived immune “guards” in breast tissue
Led by Dr. Sherene Loi, oncologist and researcher at the Peter MacCallum Cancer Centre, the study analyzed breast tissue samples from 260 women between the ages of 20 and 70, representing a diverse range of backgrounds.
The researchers discovered that women who had breastfed had significantly higher levels of specialized immune cells known as CD8+ T cells. These cells patrol breast tissue like guards, ready to recognize and attack abnormal cells that could turn malignant. Some of these cells were found to persist in breast tissue for up to 50 years.
In follow-up studies, mice that went through pregnancy, lactation, and weaning showed a surge of these same protective T cells. When exposed to aggressive breast cancer cells, those mice had slower tumor growth than those that had not nursed—suggesting the immune system “remembers” the experience of lactation and keeps up its guard.
Why this matters for maternal health
Breastfeeding has long been associated with a 4.3% lower risk of breast cancer for every year of nursing, according to research published in Cancer Medicine. What’s been unclear is why this protective effect exists.
The Nature study offers a key clue: by stimulating the production of specialized immune cells, breastfeeding may leave behind an immune imprint that continues to identify and respond to abnormal changes.
Dr. Loi and her colleagues believe this discovery could help researchers design new ways to strengthen immune resilience or develop breast cancer prevention strategies modeled after the same mechanism. It may also explain why some women are naturally more protected from aggressive forms of the disease than others.
At the same time, experts emphasize that this research doesn’t mean breastfeeding prevents breast cancer outright. Many other factors: such as age, genetics, and hormone exposure, shape an individual’s risk.
Related: Over half of moms stop breastfeeding early—and it’s not for the reason you think
Science continues to uncover the body’s brilliance
This study adds to growing evidence that pregnancy and postpartum changes influence long-term health in powerful ways. Scientists think these immune cells originally form to help prevent infections such as mastitis, but they may also help patrol for early cancer cells later in life.
Understanding this connection could have meaningful implications for cancer prevention and treatment in the future. For now, it serves as a reminder of how intricately the maternal body adapts and protects.
Related: Breastfeeding just got less stressful: This new device shows how much milk your baby is drinking in real time
A personal choice, a powerful insight
Researchers emphasize that breastfeeding remains a personal choice and is not always possible for every mother. This research offers a deeper understanding of the ways a mother’s body continues to protect and adapt.
For many parents, findings like these are both humbling and affirming. They reveal how much the body continues to give, even years after the baby stage has passed.
Science keeps uncovering what many moms have felt all along—the work our bodies do in those early months of nurturing continues to protect us long after.
Sources:
Nature. 2025. “Parity and lactation induce T cell mediated breast cancer protection”
Cancer Medicine. 2023. “Breastfeeding reduces the risk of breast cancer: A call for action in high-income countries with low rates of breastfeeding”
https://www.mother.ly/health-wellness/womens-health/breastfeeding-immune-cells-cancer-protection/?brid=H9Wfwvq06KuBj0KtonSzYg
