Breastfeeding for 6 months or more may lower the risk of childhood leukemia, according to a recent systematic review and meta-analysis of 18 case-controlled studies.
Breastfeeding for at least 6 months may prevent approximately 14%-19% of all childhood leukemia cases, estimated Efrat Amitay, Ph.D., and Dr. Lital Keinan-Boker of the University of Haifa (Israel) School of Public Health (JAMA Pediatr. 2015 June 1;169:e151025 [doi:10.1001/jamapediatrics.2015.1025]).
Among all case-controlled studies in PubMed, the Cochrane Library, and Scopus between January 1960 and December 2014, the researchers identified 18 articles comparing exposure to breastfeeding to outcomes of leukemia, involving 10,292 leukemia cases and 17,517 controls. In the full meta-analysis of all the studies, children were 19% less likely to develop leukemia if breastfed for at least 6 months than if they were breastfed for less than 6 months or not at all (odds ratio, 0.81).
An analysis of 15 studies with data on never-breastfed infants found that leukemia risk dropped 11% for children ever breastfed, compared with those never breastfed, although studies defined “never breastfed” differently (OR, 0.89).
When researchers considered only the 11 studies that examined acute lymphoblastic leukemia, with a total of 5,745 cases and 12,764 controls, breastfeeding for at least 6 months reduced acute lymphoblastic leukemia risk by 18%. Separately, six studies involving 854 cases and 9,542 control individuals found no association between acute myeloid leukemia and breastfeeding.
The authors suggested several possible mechanisms for the findings, including differences in the gut flora of breastfed infants, compared with nonbreastfed infants and the ingestion of stem cells in the breast milk that may, based on animal model research, provide active immunity.
“Breast milk is a live substance, containing antibodies and having a prebiotic effect that promotes a healthy microbiome in the intestines, some specific to the baby such as antibodies to pathogens to which each baby’s mother was exposed,” the researchers wrote.
Breast milk contains immunologically active components and multifactorial anti-inflammatory defense mechanisms that influence the development of the immune system of the breastfed infant, the researchers wrote, including secretory IgA antibodies, oligosaccharides, and lactoferrin, which can reduce inflammatory responses. They also noted that studies have found a higher concentration of natural-killer cells in breastfed babies than in formula-fed infants.
Among the meta-analysis’s limitations were the observational and noncausal nature of case-controlled studies and the wide range in response rates in the studies: 47%-98% for cases in 13 studies and 71%-95% for controls in 10 studies. Further, not all studies clearly distinguished between exclusive and partial breastfeeding.
The researchers reported having no financial disclosures.