Iron is a ubiquitous metal that is found in most cells within the human body. It is a critical
ingredient for effective red cell production but also plays a role in other biochemical
pathways including myoglobin formation, energy metabolism, neurotransmitter
production, collagen formation, and immune system function.3 Approximately 1 to
2 mg of iron enters and leaves the body daily. Gastrointestinal (GI) absorption of
iron occurs primarily in the proximal duodenum and is a tightly controlled process
that is responsive to iron status, erythropoietin demand, hypoxia, and inflammation.
The main regulator of iron absorption is hepcidin, which serves as a negative regulator
of iron absorption and macrophage iron release.4
Within the body, iron is distributed in 3 pools including transport, functional, and
storage iron.3 Absorbed iron is bound to transferrin for transport in the plasma and accounts
for only 0.1% of total body iron. Functional iron accounts for 75% of the total
body iron and is predominantly used for hemoglobin production (70%) with the
remaining in muscle and other tissues. Excess iron is stored in tissues (primarily liver,
bone marrow, and spleen) as ferritin. The amount of daily iron absorption is low relative
to ongoing demands necessitating iron recycling of senescent red cells by macrophages.
Although iron absorption is tightly regulated, there is no mechanism to regulate
iron loss.
At birth, infants have high total body iron stores (75 mg/kg of iron).5,6 These iron
stores support rapid neonatal growth but are only adequate until about 6 months of
age. At this point, iron-enriched cereals should be included in the first foods introduced
into an infant’s diet. In preterm infants, the total body iron stores are decreased
compared with full-term infants although the proportion to body weight is similar.7 Preterm
infants should receive iron supplementation because they undergo more rapid
postnatal growth than full-term infants and exhaust their iron stores by 2 to 3 months