Iron receives more attention in infant nutrition than any other single nutrient. The reason is a stored supply with a predictable end date rather than a general concern about diet quality.
The store is built before birth
Iron is transferred to the baby across the placenta, with the largest share accumulating in the final weeks of pregnancy.
That store, together with iron released as the high red cell count present at birth falls back, supplies much of what a baby needs for the first months of life.
Babies born preterm accumulate less because they miss part of that transfer window, which is why their iron status is monitored separately and often supplemented under clinical supervision.
The store runs down on a schedule
Growth in the first year is rapid, and expanding blood volume consumes iron continuously. The stored supply depletes over the first half-year in most babies.
Milk alone contains relatively little iron. Breast milk iron is well absorbed but present in small amounts, and formula is fortified precisely because of this.
The timing of the depletion is one of the reasons complementary feeding is introduced around the middle of the first year rather than later.
Absorption depends on the form and the meal
Iron in meat is absorbed considerably more efficiently than iron from plant sources, because the two are handled by different pathways in the gut.
Absorption of the plant form is increased by vitamin C eaten at the same meal and reduced by compounds in tea, some whole grains and pulses, and by large amounts of calcium.
This is why the composition of the meal matters as much as the iron content of any single food, and why a diet can look adequate on paper and function differently.
Toddlers are the second risk period
Iron deficiency is common in the second year, and a frequent contributor is large volumes of cow's milk displacing iron-containing foods from a limited appetite.
Milk is filling, low in iron, and can reduce absorption from the rest of the meal, so intake rises while iron status falls.
Signs of deficiency are non-specific, including tiredness, pallor and irritability, which makes it difficult to identify at home and a matter for testing rather than assumption.
Why it is taken seriously
Iron is required for oxygen transport and for processes in the developing brain, and the concern with deficiency in early childhood relates to development as well as to anaemia.
Deficiency exists on a spectrum, and stores can be depleted well before anaemia appears on a blood test, which is why history and diet are asked about alongside results.
Assessment and any supplementation are clinical decisions, since excess iron is harmful and iron preparations are a common cause of poisoning in young children.