Does Breastfeeding Prevent Breast Cancer?

Around the world, a woman is diagnosed every 14 seconds with breast cancer, according to the Breast Cancer Research Foundation (BCRF), making it a continued global health concern. And even though there are various factors that contribute to one’s breast cancer risk, recent studies have shed light on a connection between breastfeeding and breast cancer.

So, does breastfeeding prevent cancer? The answer, according to researchers, is no—you cannot prevent breast cancer by nursing, but yes, nursing, whether you are feeding from breast or pumping full-time, does lower your risk.

To learn more, we asked top maternity and oncology experts to help explain the link between breastfeeding and breast cancer, other benefits of breastfeeding, and what else can be done to decrease your risk of the most common cancer in women.

As rewarding as breastfeeding can be, it takes time, dedication, and a whole lot of work. One perk—beyond bonding with baby and keeping a tiny human alive and well-nourished—is lowering your odds of cancer. “In general, we know breastfeeding reduces the risk of breast cancer,” says Nawal Kassem, M.D., an assistant professor of medicine and breast oncology at the Indiana University School of Medicine in Indianapolis, IN.

Dr. Kassem points to a study published in The Lancet that included more than 50,000 women with invasive breast cancer and nearly 100,000 women in a control group. The results of that study found that the risk of breast cancer decreased by 4.3% for every 12 months of breastfeeding. (Each birth also decreased risk of breast cancer by 7%.)

“Based on this study, we also know that breastfeeding does not have to be continuous [to have this benefit],” Dr. Kassem says. You can breastfeed one of your children for six months and then breastfeed another one of your children for six months and it still “counts” as a year of breastfeeding. It’s the cumulative time that makes the difference.

So, how much does 4.3% really matter? “This is a fairly modest [breast cancer] risk reduction,” says Therese Bartholomew Bevers, M.D., the medical director of the Cancer Prevention Center at The University of Texas MD Anderson Cancer Center in Houston, TX. Though it’s not huge—it’s also not an insignificant number. “Every little bit you can eek out is beneficial,” she says.

That’s because, according to literature from the University of California, San Francisco, your individual risk of breast cancer is based on many different factors, including:

• Age

• Breast density

• Family history

• Genetics (such as carrying a BRCA gene mutation)

• Having overweight or obesity

• Lifestyle factors like alcohol intake or smoking status

• Race and ethnicity

Though the why behind breastfeeding reducing breast cancer risk isn’t fully understood, experts have some ideas. The breastfeeding benefit may have to do with the fact that exclusive breastfeeding often suppresses ovulation, which results in decreased circulating hormone levels, explains Dr. Bevers.

Specifically, during breastfeeding, your levels of the hormone prolactin are high, resulting in lower estrogen and progesterone in the body, hormones that may fuel certain breast cancers, per the American Cancer Society.

Though that’s the leading theory, says Dr. Kassem, she adds that another thought is that during the weeks, months, or years spent breastfeeding, breast cells are more stable and less likely to mutate. The cellular stability that’s a byproduct of breastfeeding could help reduce the likelihood of abnormal cell and cancerous tumor growth.

Breastfeeding is one—but certainly not the only—preventative measure you can take to lower your breast cancer risk. And if you aren’t able to breastfeed or have made the choice not to, you do not have to worry that you’re doing yourself any harm. “We certainly don’t want to put pressure on women because they aren’t breastfeeding,” says Dr. Bevers. “There are other ways to reduce your risk of breast cancer.”

Research on more than 300,000 people in the UK found that five core healthy lifestyle behaviors conferred about a one-third reduction in the risk of all cancers (including breast cancer) compared to people who practiced none or just one of these, per a recent study in the journal ecancer. These behaviors are:

• Avoiding smoking

• Limiting alcohol

• Maintaining a healthy weight

• Staying physically active

• Trying to eat a healthy diet

Let’s take a closer look at the breast cancer prevention habits to follow:

Don’t Smoke

In research on 100,000 women, those who reported having ever been a smoker were 14% more likely to develop breast cancer compared to never-puffers, found a study in Breast Cancer Research. If you’re a current smoker, all is not lost—even among women diagnosed with breast cancer who were current smokers, those who quit had a 33% lower risk of dying from breast cancer, notes 2021 research in Cancers.

Limit Alcohol

The sober-curious trend is good for breast cancer prevention. As the World Health Organization plainly puts it: “There is no safe level of alcohol consumption,” noting that the risk of breast cancer increases for every drink per day. If you’re currently working on cutting back, Dr. Hassem recommends trying to limit yourself to less than four alcoholic drinks per week. Abstaining altogether is even more critical if you have a breast cancer gene mutation, she says.

Maintain a Healthy Weight

Fat cells are the main source of estrogen production in postmenopausal women, points out research in The Journal of Steroid Biochemistry and Molecular Biology. “Women who are overweight or have obesity have higher levels of circulating estrogen, which may be why they have a higher risk of developing breast cancer,” says Dr. Bevers. Your BMI can’t tell you everything and is limited in its usefulness, but doctors often use this as a starting point to assess your weight and potential health risks. Here’s how to calculate your BMI and see where you fall.

Stay Physically Active

Whether you like to take a walk, ride your bike around town, or go to the gym to lift weights, any activity is a win for breast cancer prevention. “We don’t fully understand the reason why, but it may be because exercise helps maintain a healthy body weight,” says Dr. Bevers.

Try to Eat a Healthy Diet

“We recommend a diet that’s largely plant-based, which means one that contains vegetables, fruits, whole grains, legumes, and nuts, which reduces cancer risk overall, including breast cancer risk,” Dr. Bevers says. For general cancer prevention, the American Institute for Cancer Research also recommends reducing your intake of red and processed meats and added sugar. The thinking is that high-fat diets may lead to extra fat stores on the body; those extra fat cells make estrogen, leading to extra breast cell growth.

If you are someone who’s been diagnosed with breast cancer and you are pregnant or have a young family, you may wonder if you can still breastfeed while you have breast cancer. It depends, says Dr. Kassem. “For women who had been diagnosed with and treated for breast cancer in the past and then were able to go on and have a child, there is no reason they can’t breastfeed,” she says. Note that she is referring to women who are not currently in treatment.

However, if you’re currently undergoing breast cancer treatment, specifically hormone therapy, you would have to temporarily stop treatment in order to breastfeed, as these medications can pass through breastmilk. It may or may not be advisable for you to put your treatment on pause, so have a detailed discussion with your provider about what your best options are.

For patients on chemotherapy, Dr. Kassem recommends they stop breastfeeding. It is usually okay if you breastfeed up until starting treatment.

If you’ve had both breasts removed with a double mastectomy, it won’t be possible to breastfeed since the milk ducts are removed in surgery. If you’ve had a single mastectomy, you may be able to breastfeed from your remaining breast. Keep in mind, though, that certain cancer treatments like radiation can affect how much, or if any, milk you can produce. Talk to your doctor about the right ways to nourish your baby if you’ve had a mastectomy for breast cancer.

Breastfeeding has been shown to decrease the risk of breast cancer by 4.3% for every 12 months spent nursing, and the duration can be broken up across multiple children. That’s a modest decrease, but may be even more critical if you already have a higher risk due to family history of the disease, suggests a 2023 editorial in Cancer Medicine.

At the end of the day, breastfeeding may be helpful in lowering your odds of cancer, but there are plenty of other ways you can reduce breast cancer risk. Other impactful things that decrease your risk of breast cancer include not smoking, limiting or abstaining from alcohol, maintaining a healthy weight, exercising, and eating a healthful diet. “Breast cancer is the most commonly occurring cancer in women other than skin cancer. You can feel empowered to do things in your life that will reduce that risk,” Dr. Bevers.