If you’re a black woman with plans to have a lot of kids, you might want to breastfeed them. Why? Because African-American women are especially susceptible to a specific form of breast cancer that isn’t linked to estrogen or progesterone levels—unless, a new study suggests, they breastfeed. After tracking 47,000 black women for 13 years, researchers discovered that those who had more children were more susceptible to the cancer than those who had one or none, but that breastfeeding counteracted much of that risk, the LA Times reports.
Researchers’ theory is that, since Africa is home to a wealth of infectious diseases, women of African descent may have developed a strong immune response to pregnancy, opening the door to cancer. Lactation seems to reduce the effect. African-American women have a higher birth rate than white American women, but tend to breastfeed less—something the study’s authors hope will change thanks to the report. While only one in four breast cancers are the estrogen or progesterone receptor-negative type, they are typically more aggressive and more difficult to treat. (Read more breast cancer stories.)