Breast-feeding for at least 6 months was associated with a lower risk for childhood leukemia compared with breast-feeding for a short time or not at all, according to an article published online June 1 in JAMA Pediatrics.
Leukemia accounts for about 30% of all childhood cancers, but its causes are poorly understood. Incidence increased from 1975 through 2011 at a rate of about 0.7% per year.
Efrat L. Amitay, PhD, MPH, and Lital Keinan-Boker, MD, PhD, MPH, from the University of Haifa, Israel, conducted a meta-analysis that explored the association between breast-feeding and childhood leukemia. They identified 18 studies that met the criteria of being case-controlled, included number of months of breast-feeding, and had leukemia as an outcome. The researchers used data from PubMed, the Cochrane Library, Scopus, and manual searches of citations in published papers, covering January 1960 through December 2014.
Breast-feeding for at least 6 months was associated with a 19% lower risk of developing childhood leukemia (odds ratio, 0.81; 95% confidence interval [CI], 0.73 - 0.89) compared with breast-feeding for a shorter duration or no breast-feeding. In addition, a separate meta-analysis included the 15 studies that had data for never-breast-fed, with an 11% lower risk for childhood leukemia for those children who were ever breast-fed (odds ratio, 0.89; 95% CI, 0.84 - 0.94).
"Based on the current meta-analysis, 14% to 19% of all childhood leukemia cases may be prevented by breastfeeding for 6 months or more, a highly accessible and low-cost public health measure," the investigators conclude.
Several putative mechanisms might account for the association. The researchers hypothesize that the immune system components that are transferred in human milk, including natural killer cells and stem cells, may protect against the development of leukemia. The timing of many leukemia cases in early childhood, when infections are common, and the viral etiology of some cancers, support the immune protection hypothesis.
The different microbiome in the child resulting from drinking human milk compared with formula is another possible explanation for the inverse association between breast-feeding for more than 6 months and leukemia risk.
The authors call for further investigation of the link between breast-feeding and development of childhood leukemia.
A limitation of the investigation is that the analyzed studies were case-control observational and therefore might have had selection bias. Data were based on maternal recall, and mothers of sick children may have been more likely to accurately remember breast-feeding details. The studies varied greatly in response rate. In addition, the definition of "never breast-fed" differed among the evaluated studies.
The authors have disclosed no relevant financial relationships.
JAMA Pediatrics. 2015;169:e151025. Full text
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