Can Having a Baby and Breastfeeding Lower Your Breast Cancer Risk?

Yes! We've understood this association for hundreds of years, but recent research has provided new, sophisticated explanations.

Breastfeeding has many maternal benefits that get a lot less publicity than all those amazing advantages for baby. Ask any nursing mom to name a health benefit to her baby, and she'll rattle off several well-known protections, but she may struggle to come up with a single statistic that pertains to HER health. A wealth of research tells us that breastfeeding is protective for women against many diseases. In fact, you decrease your risk of breast cancer with each term pregnancy and every month that you spend lactating. Add them up, and the greater the number, the more significantly you have decreased your risk of all types of breast cancer, especially triple-negative breast cancer, which is typically premenopausal, and difficult to treat. And wait, it gets better....if your nursing babe is a girl, you'll reduce her risk of premenopausal breast cancer by providing your milk.

Less estrogen exposure, and specialized T cells:

This almost sounds too good to be true, so what's the science behind it? Consider that when the disease of breast cancer was first identified and reported by the Italian physician Bernardino Ramazzini in the early 1700's, he named it the "disease of nuns," because it was more prevalent in this population of women who neither carried or nursed a child. The reason for this distinction is hormonal, stemming from the fact that with every cycle of ovulation, women are subject to peaks of estrogen. During pregnancy and lactation, when ovulation is suppressed, our lifetime exposure to estrogen is reduced. This helps protect against certain types of breast cancer that are estrogen-fed. However, a new study published in October of 2025, in the prestigious medical journal Nature, established a link between immune cells in the healthy breast tissue of women who have birthed and breastfed, that seem to protect against Triple Negative Breast Cancer in particular, both in lowering the incidence of this cancer, and reducing the size of the tumors when it does occur. Triple Negative Breast Cancer is not estrogen-fed, but seems to be vulnerable to what the researchers described as "T cell mediated immunity;" and the more children you've had and the longer you've breastfed, the higher the accumulation of the protective T cells in your breasts.

Get out your calculator

My Actuary friend helped me with this formula, and it was a lot more complicated than I originally thought!

In 2002, a report in the esteemed journal Lancet, demonstrated a 7% decreased risk of breast cancer per pregnancy, and a 4.3% reduction for every 12 months of breastfeeding. So if you had 3 kids and nursed them for 1, 2, and 3 yrs respectively, (2 yrs is recommended by the American Academy of Pediatrics) you will have reduced your relative risk by 38.7%, as the example above demonstrates. Cutting the incidence by more than a third is a pretty big deal, not to mention your decreased risk of ovarian cancer, type 2 diabetes, cardiovascular disease, and more...all of which show a dose-dependent response, so the longer you breastfeed, the stronger the protection. And keep in mind the defense that you are conveying to your daughters as you breastfeed them, as described in a 2005 meta-analysis which noted a decreased risk of premenopausal breast cancer in women who had "ever been breastfed" as infants.

We know that providing human milk for our babies is important, but it should be just as well known that it's good for us lactating parents as well! So if on some days, your morale is low and you feel like you're sacrificing a lot for this little person who ruined your belly button and keeps you awake all night, think about what you're doing for yourself, as you lactate. Think about the accumulation of cancer fighting T cells that are stacking up in your breast tissue, ready to attack a tumor cell if any of them dare show up, even decades after you've weaned. Keep going, as a gift to yourself!

1. Virassamy, B., Caramia, F., Savas, P. et al. Parity and lactation induce T cell mediated breast cancer protection. Nature (2025). https://doi.org/10.1038/s41586-025-09713-5

   https://www.nature.com/articles/s41586-025-09713-5

2. Collaborative Group on Hormonal Factors in Breast Cancer. Breast cancer and breastfeeding: collaborative reanalysis of individual data from 47 epidemiological studies in 30 countries, including 50302 women with breast cancer and 96973 women without the disease. Lancet. 2002 Jul 20;360(9328):187-95. doi: 10.1016/S0140-6736(02)09454-0. PMID: 12133652. https://www.thelancet.com/journals/lancet/article/PIIS0140-6736(02)09454-0/abstract

3. Martin RM, Middleton N, Gunnell D, Owen CG, Smith GD. Breast-feeding and cancer: the Boyd Orr cohort and a systematic review with meta-analysis. J Natl Cancer Inst. 2005 Oct 5;97(19):1446-57. doi: 10.1093/jnci/dji291. PMID: 16204694. https://pubmed.ncbi.nlm.nih.gov/16204694/