By Karen Miles, IBCLC
The words “breast cancer” can evoke so much heartache and anxiety. Seeing those two words float across your phone screen while scrolling online headlines, or hearing the words whispered in a passing conversation, may bring to your mind a recently diagnosed friend or relative who is dear to you, or maybe even yourself and your own breast cancer risk. That’s because in the United States, breast cancer is the “second most common cancer among women,” with skin cancer being the number one, says the Centers for Disease Control (CDC).
Wouldn’t it be nice if currently cancer-free women could shrink their future breast cancer risk? Sure, the typical cancer-prevention trio can help: maintain a healthy diet and weight, exercise regularly, and eliminate or at least cut back on alcohol, among other things. (Check out, and share with your gal pals, this great video containing even more breast cancer risk-reduction tips.) If you are a woman, there is one additional powerful thing you might consider. You may even be doing it right now, and – surprise-surprise! – it can lower breast cancer risk: breastfeeding.
Mounting research shows that breastfeeding is truly like a gift mothers give to themselves, when it comes to reducing their own breast cancer risk. But how long do women need to breastfeed to reap this potential benefit, and what mysterious thing happens behind the scenes in a woman’s body during breastfeeding to bring about some level of breast cancer prevention for that person? I dove into the existing research to find out.
What duration of breastfeeding reduces the odds of breast cancer?
Studies are mixed on how long women need to breastfeed to score some of this reduced-risk benefit for themselves but are fairly consistent in concluding: the longer the better. Renowned medical oncologist Sherene Loi, M.D., Ph.D., recommends at least six to 12 months of breastfeeding in her March 2025 iLactation presentation, “Parity and lactation enhances immunity and protects against breast cancer.”
If your breastfeeding goal is 12+ months, here’s an incentive from the research to keep going: “The results of the reviewed studies consistently show a decreased risk of breast cancer associated with breastfeeding, especially for 12 months or longer,” summed up Cureus journal authors Abaham et al, in their 2023 review of the research.
In fact, the maternal benefit of 12 or more months of breastfeeding can be huge, not just for breast cancer risk reduction, but for lowered risk of ovarian cancer, too. Total lifetime “Breastfeeding >12 months was associated with reduced risk of breast and ovarian carcinoma by 26% and 37%, respectively,“ found another review and meta-analysis, published in Norway.
But continuing a breastfeeding journey any amount of time may help. That’s because the relationship between breastfeeding and reduced breast cancer risk is dose-dependent, according to Ugandan authors Emmanuel Ifeanyi Obeagu and Getrude Uzoma Obeagu in their 2024 review of the evidence in the open access journal Medicine. They found that for women, “Each additional month or year of breastfeeding has been associated with a modest but incremental decrease in the risk of developing breast cancer.”
How does breastfeeding lower breast cancer risk?
Scientists are still exploring the mechanism by which breastfeeding lowers breast cancer risk, and multiple factors may be at play.
Hormonal changes that occur during breastfeeding, such as lowered estrogen, may prevent breast cells from multiplying and malignant ones from forming. The milk ejection hormone, oxytocin, may also serve as a shield against breast cancer by impacting the growth and differentiation of cells in breast tissue.
The process of internal breast reshaping that happens during breastfeeding, as well as post-breastfeeding after the breasts return to “normal,” may help sweep out damaged cells in the breast tissue, suggest several researchers.
In addition, an increase in special immune cells called “CD8+ T cells” in the body appears to occur during pregnancy and breastfeeding, and those T-cells can stick around for many years, according to research done in mice, as well as human populations. These friendly immune cells may stand guard against one of the most aggressive types of breast cancer, triple negative breast cancer.
Unfortunately, there are few certainties in life. Some women are diagnosed with breast cancer before, after, and even during breastfeeding – even those who seem to have no major lifestyle risk factors and who have no family history of breast cancer. (So keep up with your mammograms!) And not everyone is able to breastfeed. But nonetheless, these research findings are terrific news for any woman who is able to, and chooses to, breastfeed. On hard days, it is a compelling reason to continue another minute, month, or year.
Karen Miles is an International Board Certified Lactation Consultant (IBCLC) and Lactation Content Specialist with Milkify.
This article is for informational purposes only and is not intended to diagnose, treat, or be a substitute for medical advice. Please consult with your healthcare provider for any questions you may have related to your own health, or your baby’s health.
