Homeostatic Regulation of Iron and Its Role in Normal and Abnormal Iron Status in Infancy and Childhood

Abstract

Iron is important in neurodevelopment and cognitive function, and globally preventing iron deficiency and iron deficiency anemia remains a high priority. Term breast-fed infants and infants fed an iron-fortified formula usually have a satisfactory iron status during the first 6 months of life, but there are still ambiguities in assessing iron status in infants and how to properly meet their iron requirements. This is particularly evident for preterm infants, who are born with low iron stores, and for whom recommendations for iron provision vary considerably. In part, this may be due to immaturity in the regulation of iron homeostasis in young infants. Whereas 9-month-old infants appear to be able to downregulate iron absorption when being iron replete, 6-month-old infants cannot do this. Iron may be provided as drops or in iron-fortified products, but the forms provided may be metabolized differently, and excess iron in drops may cause adverse effects, possibly due to a limited ability to regulate iron absorption in young infants. Adverse effects are manifested by decreased growth: in well-nourished infants by reduced gain in length, in poorly nourished populations by lower gain in weight. The mechanism behind the decreased growth is not known, but it may involve free radical-mediated effects of iron or an interaction with zinc absorption/homeostasis. It therefore seems that iron drops should not be given to iron-replete infants.