Metabolic implications of iron in breast milk
In: Handbook of dietary and nutritional aspects of human breast milkSearch for other papers by C. Breymann in
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Iron is an essential element and micronutrient for various body functions and vital metabolic processes. Deficiency impairs haemoglobin and myoglobin synthesis, muscle and nerve function, psychomotor development, cognitive function, enzyme activity, thermoregulation and the immune system. Normal body iron content is 3-4 g (40-50 mg/kg body weight). Iron is absorbed under the influence of active transport systems in the intestine, before being bound and transported by transferrin to the organ systems and stored by the storage protein ferritin. Little is known about iron entry into breast milk but it is probably enabled by the transferrin receptors on mammary plasma membrane. Other iron transporters that might be involved are divalent metal transporter-1 and ferroportin-1. There is no evidence that iron is stored in the mammary gland during lactation. Breast milk iron concentrations show individual and diurnal variation and, in some studies, a decline during the course of lactation, while other studies report them as stable. Iron absorption from breast milk and bioavailability are high in neonates and infants, due in part to enhanced expression of iron absorption proteins and transporters, as in adults, but the precise mechanism remains unclear. Although diet and nutritional status influence the nutrient composition of breast milk in general, they do not significantly affect total energy or energy nutrient ratios. However, poor nutritional status in terms of iron intake impacts breast milk iron content. Iron status in the neonate and infant depends mainly on prenatal iron availability, i.e. on the ability of the foetus to accumulate iron during pregnancy. If foetal stores are adequate, breast milk normally supplies enough iron for infants up to 6 months, after which supplementation is recommended in exclusively breast-fed infants. In neonates born to iron-deficient mothers, on the other hand, postnatal iron stores are probably insufficient to meet iron needs and will usually fail to normalise on breast milk alone.