Breastfeeding and Breast Cancer: Does Breastfeeding Lower Breast Cancer Risk?

BCRF looks at the link between breastfeeding and breast cancer risk, plus what to know if you don’t breastfeed

Many women who breastfeed do so primarily for their baby’s health, but it may offer benefits for their own health, too. Breastfeeding triggers hormonal shifts that may lower a woman’s risk of developing breast cancer.

That’s good news for women who breastfeed. However, breastfeeding only plays a part in an individual’s chances of getting breast cancer. Many other risk factors, including age, race, genetics, diet, and more, also contribute to a person’s overall risk. So even if you can’t or choose not to breastfeed, there are other ways to lower your risk, bond with your baby, and support their nutritional needs.

Whether you breastfeed for days, months, or not at all, understanding the link between breastfeeding and breast cancer risk can provide valuable information as you weigh your decisions.

Does breastfeeding lower breast cancer risk?

Long-standing research consistently shows that breastfeeding can reduce the risk of breast cancer. This includes a 2002 report in the prestigious journal Lancet, which evaluated data across 47 epidemiological studies on more than 50,000 women with breast cancer and nearly 100,000 women without the disease. It found that the relative risk of breast cancer declined by 4.3 percent for every 12 months a woman breastfed.

A 2013 meta-analysis in the Asia-Pacific Journal of Public Health found a similar relationship between breastfeeding and breast cancer. After evaluating data in 32 studies, the researchers concluded that women who breastfed were 11 percent less likely to get breast cancer. This benefit increased to 28 percent among women who breastfed for 12 months or longer. Researchers found nearly the same result in a 2015 meta-analysis, which concluded that breastfeeding for more than 12 months reduced the risk of breast cancer by 26 percent and ovarian carcinoma by 37 percent.

This association is so strong that Lancet reported in 2016 that the current rates of breastfeeding directly prevent nearly 20,000 deaths from breast cancer every year, and an additional 20,000 lives would be saved annually by scaling up breastfeeding practices worldwide.

That being said, breastfeeding seems to have a stronger protective effect on some types of breast cancer than others. The 2015 meta-analysis noted that there was no significant association between breastfeeding and a reduced risk of hormone receptor–positive breast cancers, which account for 80 percent of diagnoses.

According to a 2024 review in Medicine, breastfeeding has been shown to lower the risk of hormone receptor (HR)-negative breast cancers, especially in those who breastfed for an extended period.

However, findings aren’t consistent when it comes to triple-negative breast cancer (TNBC). The results are mixed: Some studies found that breastfeeding offered a potential protective effect against TNBC, while others didn’t demonstrate a significant connection. A just-released BCRF-supported study found that up to 15 percent of TNBC diagnoses in Black women and 12 percent of diagnoses in white women could have been avoided by breastfeeding more than six months. Further, researchers have observed that tumors in women who’ve breastfed tend to be smaller and less aggressive.

How does breastfeeding reduce the risk of breast cancer?

Exactly how breastfeeding reduces the risk of breast cancer is likely the result of a combination of biological changes that happen in the body during and after lactation.

Hormonal changes seem to play a particularly strong role in breastfeeding’s protective effect against the disease, according to a 2024 report in Medicine. When a woman is breastfeeding, she experiences an uptick in the hormone prolactin, which stimulates milk production and suppresses ovulation. That, in turn, leads to a reduction in estrogen, a hormone that’s directly involved in the growth of certain types of breast cancer cells. The hormone oxytocin is also released while a woman is breastfeeding to help with milk ejection. Researchers have observed links between oxytocin and tumor protection, which may also help reduce the risk of breast cancer.

Changes in breast tissues that occur during breastfeeding may also play a role in reducing the risk of breast cancer. As the breast tissue remodels throughout the lactation process, the body may be able to clear out damaged or mutated cells that could otherwise turn into cancer.

Immune system shifts during breastfeeding may offer another layer of protection. Breast milk contains protective elements, like antibodies, immune cells, and cytokines, that not only help prevent infections in babies, but may also provide benefits to the breast tissue of lactating women. Scientists suspect that this may help the body identify and eliminate abnormal cells before they turn into breast cancer, but more research is needed to understand this potential effect.

How long do you have to breastfeed to lower your breast cancer risk?

There’s no magic number of months that guarantees protection, but research consistently shows that the longer you breastfeed, the greater the potential benefit. The protective effect appears to be cumulative, meaning each additional month—even when spread across multiple babies with breaks in between—may help lower your risk a little more.

The World Health Organization recommends breastfeeding for the first six months of a baby’s life to provide health benefits to both the mother and the baby. The risk of breast cancer drops by 26 percent among women who breastfeed for more than 12 months, per a 2015 meta-analysis. The 2002 report in Lancet suggests you may get a 4.3 percent drop in the relative risk of breast cancer for every 12 months you breastfeed. An earlier study published by the American Journal of Epidemiology in 2000 found that the lifetime risk of breast cancer dropped by more than 50 percent in women who breastfed for more than 24 months and 76 percent in those who breastfeed for more than 109 months.

Taken together, these findings suggest that every month of breastfeeding may provide greater protection against breast cancer. While breastfeeding isn’t always possible or right for everyone, its benefits are significant across the population at large, an important factor in making public health recommendations. Still, each individual’s risk of breast cancer depends on a variety of factors, and those who don’t breastfeed can still support their health in other ways.

Does pumping offer the same potential benefits?

Most studies on breastfeeding and breast cancer don’t distinguish between breastfeeding and pumping. However, pumping has a similar effect on the body as breastfeeding, which may play a role in breast cancer risk.

According to a 2020 systematic review published in the Public Library of Science journal PLOS One, research has shown that mechanical breast pumping led to a release of oxytocin and prolactin—the same hormones involved in direct breastfeeding. Since these two hormones are thought to help reduce the risk of breast cancer, it’s possible that pumping may provide some of the same protection against the disease as breastfeeding. With that said, suckling is shown to contribute to the rise in maternal oxytocin levels in the first few days postpartum—an effect that may not be as strong in those who exclusively pump from the beginning.

More research is needed to understand the differences in breastfeeding and pumping when it comes to the risk of breast cancer.

What to know if you can’t breastfeed

While there’s a strong link between breastfeeding and breast cancer risk, it’s just one of many factors that influence your individual risk. Women don’t breastfeed—or don’t breastfeed for as long as guidelines recommend—for a variety of reasons. Some women and babies are not physically able to direct feed at the breast. Many women in the U.S. do not have the lactation support, paid leave, and other privileges necessary to promote breastfeeding. Other mothers simply choose not to. Not breastfeeding does not mean you’re destined to develop breast cancer. And while breastfeeding can offer a modest protective benefit, it’s far from the only way to support your long-term breast health.

There are many ways to reduce your risk of breast cancer, regardless of whether you breastfeed. This includes maintaining a healthy weight, eating less meat, incorporating more produce and whole grains into your diet, limiting alcohol consumption, and exercising. Knowing your family history and keeping up with routine screenings can also help you catch breast cancer at its earliest, most treatable stages.

Breastfeeding is a very personal decision. For some women, it’s a rewarding way to bond with their baby and provide nutrition and health benefits. For others, it’s difficult, stressful, or simply not possible. While breast cancer protection is a bonus, it’s only one part of a woman’s breastfeeding decision. Plenty of women who don’t breastfeed go on to lead healthy lives and raise healthy children. What matters most is making informed decisions that feel right for you and your family.

The bottom line

Decades of research show that breastfeeding can reduce the risk of breast cancer, perhaps due to the hormonal and tissue changes that occur during lactation. The protective effect is relatively modest in individuals, but significant at the population level, which is important for public health recommendations.

While women who breastfeed may gain some added protection against the disease, it’s just one of many factors that influence any individual’s risk of breast cancer.