Albertine Donker

Iron Function and Iron Handling from Fetus to Adult 51 2 INTRODUCTION Iron is indispensable for the normal development and function of all tissues in the human body. However, iron is also a potential toxicant to cells; unbound iron can catalyze the formation of oxidative radicals that damage proteins, lipids and nucleic acids. 1 Furthermore, although the immune system needs iron in order to defend the host against pathogens, the virulence of many infectious organisms conversely depends on their ability to assimilate iron from their host. 2,3 Therefore, the human body has to deal with two opposite forces regarding iron metabolism; the need to obtain iron from food for the synthesis of heme, hemoglobin and other iron-containing vital proteins and the opposite need to withhold iron from iron- stealing pathogens. 4 Because both iron deficiency (ID) and iron overload (IO) may have detrimental effects, a highly sophisticated regulatory system is required to maintain iron homeostasis on both the systemic and cellular level. This is particularly critical during childhood. Rapid growth and development requires greater amounts of micronutrients than in adults while (especially young) children are vulnerable to infections with iron- dependent pathogens because of a still immature immune system. Growth and development in children occurs in transition phases from fetus to adult. 5,6 Understanding the specific contribution of iron and the mechanisms of iron handling during these different stages of fetal life and childhood is crucial. This forms the basis to define measures for adequate iron supply to the growing and developing child and enable the diagnosis and tailored treatment of iron disorders associated with a defective iron homeostasis both on the cellular and systemic level. 7 In this narrative review we focus on the critical roles of iron for human growth and development during the specific transition phases from fetus to adult. Different from earlier reviews that predominantly focus on infants and young children, 8-10 we aim to cover the whole period of childhood, from conception to adulthood for both low and high income parts of the world, with a focus on the systemic iron homeostasis.