Supporting Breastfeeding

La Leche League Canada

Breastfeeding Protects Against Breast Cancer

on October 12, 2015

By Diana Cassar-Uhl.  From La Leche League International’s Breastfeeding Today, “Breastfeeding Protects Against Breast Cancer:  Primary Prevention.

When experts in disease control talk about prevention, there are three levels: primary, secondary, and tertiary.  The aim of primary prevention is to keep the disease from occurring; secondary prevention focuses on those who have the disease, but are not suffering ill effects from it (or perhaps don’t yet know they have it). Tertiary prevention works to minimize the impact of the disease on the affected person — to make living with the disease as easy as possible.

The most complete form of prevention is primary — avoiding the disease altogether.  Yet, when we, as a culture, look at “prevention” of breast cancer, efforts are typically focused on secondary prevention — early detection.  Monthly breast self-exams and mammograms according to our age and family history are methods of “prevention” that help us to find the disease that may already be there.  While early detection and treatment save lives, primary prevention of breast cancer is the ideal “cure.”  Every day, we’re bombarded with messages about how to prevent cancer:  reduce pesticide exposure, eat organic foods, eat less animal protein and more plant-based foods, etc.


How do we know which measures actually affect our cancer risk, specifically our risk for developing breast cancer?

In 2007, in an effort to establish whether certain lifestyle factors offered any preventive measure against various types of cancer, the American Institute for Cancer Research released a report of a meta-study it had conducted (over five years, compiling results from several smaller studies).

Of all the factors that were examined, many were shown to offer “probable decreased risk” or “limited-suggestive decreased risk;” these lifestyle factors might offer protection against cancer, but the evidence wasn’t strong enough to confirm that they definitely protect us.

The meta-study found, however, two factors that provide “convincing decreased risk;” that is, two lifestyle factors were shown to be convincingly preventive against cancer:

Regular exercise is one; breastfeeding is the other!

Breastfeeding provides convincing decreased risk against breast cancer.  This particular meta-study reported that breastfeeding provides up to a 28% decrease in risk of developing breast cancer at any age (pre- or post-menopausal) for women without a family history of the disease, who breastfed for 12 months or longer (World Cancer Research Fund and American Institute for Cancer Research, 2007).

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Similar findings were reported in other studies:

  • In an eight-year study of over 60,000 women who had given birth, having ever breastfed provided up to a 59% reduction in the risk of developing premenopausal breast cancer in women with a family history of the disease (Stuebe, Willet, Xue, & Michels, 2009).  That means, for women with a family history of breast cancer, breastfeeding can reduce your odds of developing pre-menopausal breast cancer by more than half!
  • In another meta-study (compiling data from 47 smaller studies) published in 2002, more than 50,000 women with breast cancer and nearly 97,000 women without the disease, from 30 countries, were studied.  After standardizing the data for age, menopausal status, and economic standing of her country (so that these factors did not influence the results), this study concluded that a woman who breastfed for 12 months in her life reduced her risk of developing breast cancer by 4.3%.  This benefit can be multiplied as a mother breastfeeds one child or several children and logs months and years of lactation.  For example, a mother who has two children and breastfeeds each for two years can realize a 17.2% reduction in her risk of developing breast cancer later in her life (Collaborative Group on Hormonal Factors in Breast Cancer, 2002).

This is due to the fact that exclusive breastfeeding suppresses a woman’s menstrual cycle, thereby reducing her lifetime exposure to estrogen, which “feeds” many breast cancers.  When breastfeeding comes to an end the mother’s body rids itself of any cells in the breast that may have DNA damage and this reduces the risk of breast cancer developing in the future.  It is important to note that duration of breastfeeding, the longer a mother breastfeeds in her life (one or more babies and the collective number of months), significantly impacts her risk for breast cancer; the protective effect of lactation on breast cancer risk is cumulative.  This is one explanation for why developed countries, whose mothers breastfeed for shorter durations (or not at all) and have fewer children in their lifetimes, have higher rates of breast cancer among their populations.

In addition to offering protection from breast cancer to the mother, having been breastfed has a protective effect.  One study cites a 26–31% decrease in the development of breast cancer in females who had been breastfed as babies:   if you or she takes no other preventive measures against breast cancer, breastfeeding her alone sets your baby girl up for a nearly 1/3 lower likelihood of developing breast cancer later in her life (Freudenheim et al., 1994).

In the 2007 American Institute for Cancer Research report, obesity and overweight were cited as major risk factors for the development of several types of cancer.  The report also concluded that breastfeeding protects infants from being overweight and obese, which tracks into later life and prevents several types of cancers in adults who were breastfed as children.

Research has long shown that breastfeeding is good for babies, providing optimal nutrition, strengthened immune systems and fewer illnesses than formula milk feeding.  Yet the advantages to a mother from breastfeeding her baby are little reported or limited to the perk of speedier weight loss postpartum.



Despite the convincing scientific evidence many mothers are unaware that breastfeeding reduces their risk of breast cancer.  Many new mothers are making choices about infant feeding without knowing breastfeeding can help reduce cancer risks for both themselves and their children.  Mothers should be entitled to have this information readily available to them when they are deciding how they want to feed their babies and all information on baby feeding provided to new and expectant mothers should be independent, free from misleading commercial promotion.

The recommendations, then, are simple:  mothers should breastfeed; babies should be breastfed. Breastfeeding provides primary preventive protection against cancer for mother and child. Ideally, breastfeeding should be exclusive until around the middle of the baby’s first year.  Exclusive breastfeeding means human milk only:   no other food or drink, including water, should be fed to the baby until around the middle of the first year of his or her life.  Breastfeeding should continue through the rest of the baby’s first year, with complementary foods being introduced, and the greatest protective effect is realized when breastfeeding continues through the child’s second year or beyond.  This is in accordance with the recommendations of the World Health Organization’s Global Strategy on Infant and Young Child Feeding.

In all of the newsworthy efforts to save our mothers, sisters, friends, and ourselves from breast cancer, how often do we hear breastfeeding mentioned as primary prevention?  Spread the word — the research is on our side!  Breastfeeding is one worthwhile measure mothers can take to reduce their risk of developing breast cancer AND protecting their daughters, as well.

From La Leche League International’s Breastfeeding Today, “Breastfeeding Protects Against Breast Cancer:  Primary Prevention” by Diana Cassar-Uhl.  For complete references and links visit

October is Breast Cancer Awareness Month in Canada.


If you need more information or have a breastfeeding problem or concern, you are strongly encouraged to talk directly to an accredited La Leche League Leader.  In Canada, Leaders can be located by clicking or Internationally


If you have found this article helpful, La Leche League Canada would appreciate your support in the form of a donation at  so we can continue to help others breastfeed. Thank you!


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