For healthy mothers and infants, there are few good reasons to eschew breastfeeding, but Israeli researchers may have found the biggest benefit of all: A study conducted by the University of Haifa in conjunction with the Israel Center for Disease Control found that breastfeeding can significantly reduce the risk of leukemia in children, even if they’re breastfed for just one month.
“This meta-analysis that included studies not featured in previous meta-analyses on the subject indicates that promoting breastfeeding for 6 months or more may help lower childhood leukemia incidence, in addition to its other health benefits for children and mothers,” the authors wrote.
Cancer is the second-most prevalent cause of death in children under 15, and leukemia is the most prevalent cancer in that age group. Leukemia, in its two most common forms, affects the way bone marrow produces blood cells. Acute myeloid leukemia results in the production of too many abnormally mutated blood cells, while acute lymphocytic leukemia causes the production of too many white blood cells. Together, the two account for 30% of all childhood cancers.
The precise reason for breastfeeding’s anti-cancer effect is unknown, but the authors reached their conclusion after reviewing 18 existing studies that examined the relationship between breastfeeding and leukemia. All told, the studies included over 10,000 children diagnosed with leukemia, and over 17,000 control subjects who were not.
The nine studies that the researchers deemed of the highest quality found that six months or more of breastfeeding resulted in a 14% decreased risk for leukemia. Using another group of studies, they found that having breasted at all (even for as little as a month) accounted for an 11% lower risk. Overall, based on the analysis of all 18 studies, breastfeeding for six months or more was associated with a 19% decreased risk of cancer.
One theory that may explain the correlation is the Greaves hypothesis, which states that some children are predisposed to leukemia due to a prenatal genetic mutation. Exposure to an “infective agent” (i.e., baby formula made with water) could be what causes the cancers to grow. If that’s the case, then breast milk may act as a sort of cancer-fighting drug, as it contains natural antibodies, gut microbes and other components that bolster a baby’s immune system.
The LA Times reports that the prevalence of childhood leukemia has increased 0.7% per year between 1975 and 2011 in the U.S. In Europe, the incidence has risen by 0.6% per year between 1978 and 1997. No one’s sure why this is the case.