Breastfeeding and Childhood Leukemia Incidence: A Meta-analysis and Systematic Review.

IMPORTANCE: Childhood cancer is a leading cause of mortality among children and adolescents in the developed world and the incidence increases by 0.9% each year. Leukemia accounts for about 30% of all childhood cancer but its etiology is still mostly unknown.

OBJECTIVE: To conduct a meta-analysis of available scientific evidence on the association between breastfeeding and childhood leukemia.

DATA SOURCES: A thorough search for articles published between January 1960 and December 2014 researching the association between breastfeeding and childhood leukemia was conducted on PubMed, the Cochrane Library, and Scopus (performed in July and December 2014), supplemented by manual searches of reference lists.

STUDY SELECTION: To be included in the meta-analyses, studies had to be case control; include breastfeeding as a measured exposure and leukemia as a measured outcome; include data on breastfeeding duration in months; and be published in a peer-reviewed journal with full text available in English.

DATA EXTRACTION AND SYNTHESIS: The search identified 25 relevant studies, 18 of which met all inclusion criteria. No publication bias or heterogeneity among these 18 studies were detected. The quality of each study that met the inclusion criteria was assessed using the Newcastle-Ottawa Scale. Multiple meta-analyses were conducted using the random effect model on raw data in the StatsDirect statistical program.

MAIN OUTCOMES AND MEASURES: No or short duration of breastfeeding and the incidence of childhood leukemia.

RESULTS: The meta-analysis of all 18 studies indicated that compared with no or shorter breastfeeding, any breastfeeding for 6 months or longer was associated with a 19% lower risk for childhood leukemia (odds ratio, 0.81; 95% CI, 0.73-0.89). A separate meta-analysis of 15 studies indicated that ever breastfed compared with never breastfed was associated with an 11% lower risk for childhood leukemia (odds ratio, 0.89; 95% CI, 0.84-0.94), although the definition of never breastfed differed between studies. All meta-analyses of subgroups of the 18 studies showed similar associations. Based on current meta-analyses results, 14% to 19% of all childhood leukemia cases may be prevented by breastfeeding for 6 months or more.

CONCLUSIONS AND RELEVANCE: Breastfeeding is a highly accessible, low-cost public health measure. 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.