Does Breastfeeding Really Reduce Your Risk of Breast Cancer?

We dug through the complicated research to help you minimize your risk.

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Most women can rattle off a couple benefits of breastfeeding: Fewer colds and illnesses? Yep. A precious way to bond? Definitely.

But things get a little murkier when it comes to one, potentially life-saving reason to breastfeed: a reduced risk of breast cancer. While plenty of research has established a link, it's surprisingly hard to get straight answers. We sorted through the studies to give you the scoop.

Does breastfeeding reduce the risk of breast cancer?

Yes, it does, though the specifics are hard to pinpoint. There are four studies worth noting.

A large-scale analysis of nearly 150,000 women published in The Lancet in 2002 found that for every 12 months of breastfeeding (either with one child or spread over multiple children), the risk of breast cancer decreased by 4.3 percent, when compared to women who didn't breastfeed at all.

Then a 2009 study of more than 60,000 women published in the Archives of Internal Medicine found that women with a family history of breast cancer reduced their risk of getting the disease before menopause by nearly 60 percent if they breastfed.

A study published this year by the Journal of the National Cancer Institute found that women of African ancestry have an especially high risk of developing the aggressive and hard-to-treat forms of breast cancer called estrogen receptor-negative and triple-negative—and the risk actually goes up when a woman gives birth—but breastfeeding negates this risk.

Finally, an international, collaborative study of almost 37,000 breast cancer cases published in the Annals of Oncology in October found a 20 percent reduction in risk of developing hormone-receptor negative breast cancer for women who breastfed. But study authors noted this hard-to-treat subtype of breast cancer is especially prevalent among populations of women who have risk factors that make them least likely to breastfeed, such as being obese, having multiple, early pregnancies, or being of African-American or Sub-Saharan African descent, and that more needs to be done to encourage women to breastfeed.

"There seems to be growing evidence that breastfeeding is associated with a lower risk of the really aggressive kinds of breast cancer," says Alison Stuebe, M.D., an assistant professor of obstetrics and gynecology at the University of North Carolina at Chapel Hill and the lead author of the Archives of Internal Medicine study.

The upshot: If you can and want to breastfeed, definitely do it, especially if someone in your family, like your mom or sister, has had breast cancer. It's even more important if your family member had a particularly fast-moving or difficult-to-treat form, or she was diagnosed under 40-years-old.

Why does breastfeeding reduce the risk of breast cancer?

Research has pointed to a few theories, though none have been proven. One is that women who breastfeed have fewer menstrual cycles throughout their lives, and therefore less exposure to estrogen, which has been shown to fuel some types of breast cancers. Another theory: Breastfeeding makes breast cells more resistant to mutations that can cause cancer.

Additionally, there are lifestyle factors that often come into play: Breastfeeding (and pregnant) women tend to give up smoking and drinking, eat healthier foods, and in general take care of themselves better. These behaviors are known to reduce your breast cancer risk.

How long should you breastfeed to reduce your risk?

We don't yet have a conclusive answer to this, but research, like The Lancet study, has pointed to a trend that longer is better. Even if you supplement with formula, it appears that breastfeeding of any kind still reduces your risk. So don't feel like it's all-or-nothing if you're struggling with supply issues.

Dr. Stuebe encourages the moms she sees in her practice to nurse for at least a year, or as long as both the mom and baby want to—in order to receive the many benefits of breastfeeding. The AAP has the same recommendation.

But if you can't breastfeed...

Don't stress about it.

"I don't want to send the message that you'll get breast cancer if you don't breastfeed, and you'll never get it if you do," explains Dr. Stuebe. "Neither of those things is true."

Don't forget that perhaps the single most effective way to help cut your cancer risk is through healthy lifestyle habits within your control. A 2008 report published by the National Institutes of Health stated a simple fact that should be repeated: "Only 5–10 percent of all cancer cases can be attributed to genetic defects, whereas the remaining 90–95 percent have their roots in the environment and lifestyle." The lifestyle factors they referenced? Things like smoking cigarettes, a diet high in fried food and red meat, drinking alcohol to excess, and lack of physical activity. That means, breastfeeding isn't the only way to reduce your risk of breast cancer: exercise and healthy-eating help, too. The bottom line? Breastfeed if you can, Mama, but don't worry too much if you can't.

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