Answer to Q22.
Iron is a nutrient of special significance to a young infant. As baby grows rapidly in the first few months, new tissues and blood cells need iron for their formation and function. Human milk has quite a low level of iron, and this may seem odd, even although for several reasons the iron which is present is exceptionally well absorbed by the baby.
The answer is that at birth, baby has a stores of iron, partly in the form of a special kind of red blood pigment called fetal hemoglobin, which after birth becomes surplus to needs and the iron can be reutilised for growth. In the early mionths, then, unless baby is for some reason losing iron [in blood loss], even the small amount in breast milk is sufficient.
By around six months, however, those stores of iron are becoming completely used. Unless a new source of iron in the diet is introduced, iron deficiency in inevitable. Studies in New Zealand, as overseas, have shown that in the age range from 6 - 24 months, iron deficiency is very common. This may be due, at least in part, to failure to add iron-rich foods at that stage.
For infants no longer breastfed, follow-on formulas are also designed to supply iron. Cow's milk or other alternatives are very poor in iron and cannot supply what is needed, explaining the importance, when breastfeeding ceases in the second six months of life, of using follow-on formula instead. Infant cereal products today are fortified with iron. Eventually of course meat and similar foods which are also rich sources of iron will be introduced.
Iron deficiency is considered a very serious problem in infancy because it is believed to interfere with normal development and maturation of the brain, and possibly also reduce the body's resistance to infection. If the iron deficiency is accompanied by anaemia [low hemoglobin level in the blood], this can reduce the ability of the baby to be physically active at the time when motor development is very brisk. For these reasons the current levels of iron deficiency which are being found in population surveys are considered serious and must be treated or, better, prevented.