Global look at nutritional and functional iron deficiency in infancy.

Iron-deficiency anemia (IDA) affects many infants in low- and middle-income countries (LMICs) and may impair cognitive development and adaptive immunity. Effective interventions to improve iron intakes for infants in LMICs are urgently needed. However, absorption of oral iron fortificants and supplements is low, usually <10%, and most of the iron passes into the colon unabsorbed. In randomized controlled trials, provision of iron to infants in LMICs adversely affects their gut microbiome and increases pathogenic Escherichia coli, gut inflammation, and diarrhea. To minimize these detrimental effects of iron, it is important to provide the lowest effective dosage and maximize fractional iron absorption. Prebiotic galacto-oligosaccharides and apo-lactoferrin may prove useful in iron formulations in LMICs because they increase absorption of fortificant iron and at the same time may mitigate the adverse effects of unabsorbed iron on the infant gut. Providing well-absorbed iron early in infancy may improve immune function. Recent data from a Kenyan birth cohort suggest IDA at the time of infant vaccination impairs the response to diphtheria, pertussis, and pneumococcus vaccines. A randomized trial follow-up study reported that providing iron to Kenyan infants at the time of measles vaccination increased antimeasles immunoglobulin G (IgG), seroconversion, and IgG avidity. Because IDA is so common among infants in LMICs and because the vaccine-preventable disease burden is so high, even if IDA only modestly reduces immunogenicity of vaccines, its prevention could have major benefits.