Albertine Donker

Iron Function and Iron Handling from Fetus to Adult 71 2 of infants and neonates, suggesting that the import of iron across the apical membrane of the enterocyte is mediated by the absorption of lactoferrin-bound iron. 8,155,166-170 Importantly, both in vitro and in vivo studies have demonstrated that lactoferrin has crucial antimicrobial, immune modulating and anti-inflammatory properties, apart from its capacity to absorb iron. 171 The antimicrobial function involves the withdrawal of iron from iron-stealing pathogens in combination with specific interactions with the bacterial wall but also with viruses and parasites, while the immune modulating and anti-inflammatory characters can be attributed to a direct effect on the migration, maturation and function of various immune cells. 171 Noteworthy, clinical trials with bovine lactoferrin added to infant formula have not shown any enhancing effect on iron absorption or iron status, which may be because bovine lactoferrin does not bind to the human lactoferrin receptor or because other constituents of the formula may interfere with iron utilization from lactoferrin. 166,172,173 An important question is if and how the human female body regulates the iron content of breast milk. Until now, a membrane iron exporter protein has not been identified in human lactacting epithelial cells, suggesting that iron reaches the breast milk by passive desquamation and not by active excretion. 158,174 This hypothesis is supported by the occurrence of iron-containing mammary epithelial cells in human milk. 158 A next clinically relevant knowledge gap concerns the influence of maternal iron supplementation on the iron content of breast milk. 175,176 A recent study showed that a single dose of intravenous iron temporally enhanced iron concentration of breast milk, but more research is warranted on this topic. 177 Iron homeostasis in infancy During the first year, the infant weight and height increase on average from 3 kg to 10 kg and from 50 cm to 75 cm respectively, 53 accompanied by an approximate increase of body iron from 270 mg to 450 mg ( Figure 1, Table 2 ). The ongoing development of the neonatal brain specifically requires high quantities of iron, although precise amounts are unknown; more than 50% of resting metabolic rate is devoted to brain growth and function during the neonatal period. 5