Early Human Iron Equilibrium: A Review

The biological equilibrium of iron,a potent, multifunctional micronutrient is a decisive factor in the holistic health of the mother and child. Iron dysequilibriumimpairs organ function, effects growth and development and predisposes to a spectrum of disease states. This article revisits the homeostasis of body iron in early life as a sequential continuum from prenatal to early post-natallife ,then reviews, compares and attempts to integrate intra and early extra uterine events related to iron metabolism. The “adaptive evolutionary” mechanisms involved in iron homeostasis in early life such as the transfer of iron from the mother to the feto-placenta unit and fromthe lactating mammary glands into breastmilk are revisited as both organs support life during dynamic developmental stages of growth and differentiation. The checks and balances of iron metabolism in pregnancy also endow some iron to the feto-placental unit, by actively transporting iron from the mother to the developing fetus. In early postnatal life the mechanisms involved in iron absorption are not yet fully mature, and other sources of iron such as transplacentally transferred iron and the iron stored from hemolysis of the rapidly decreasing red blood cell (RBC) mass contribute to early iron equilibrium. Additionally, although breastmilk is low in iron, the concept of active iron bioavailability in the breastfed infant provides utilizable iron. The lactating mammary glands may adopt unique features of iron metabolism adapted to the individual infant with the iron content in breastmilk largely, but not entirely, independent of maternal iron status. Early physiological iron equilibrium reflects essential homeostatic complexity, highlighting that exogenous iron, when required, must also be weighed for its benefits against its risks, as evident in the cautious homeostasis in our biological systems.