Non-vegetarian diet is richest source of iron containing 10-18 mg of iron per 100 grams.

Bioavailability of iron : Ultimate absorption of iron into mucosal cells mainly depends upon bioavailability of iron in the various foodstuffs. The non-vegetarian foods have iron (haem) with very high bioavailability and the absorption of this is not affected by any other factor in the lumen including various food ingredients. Absorption of iron from vegetarian sources is affected by various factors as shown in Table no. 4.

Mucosal cell control : Appropriate iron balance in the body is achieved by mucosal cell control through transferrin and apoferritin receptors. When the serum iron is normal and adequate, the iron gets incorporated into apoferritin in the mucosal cell and this is ultimately excreted after 3 - 4 days, when lifespan of mucosal cells is over. However, if iron deficiency state exists in the body, transferrin is utilized to combine with iron and is transported and stored at storage site.

Iron transport and storage : Transferrin helps in transport of iron from the intestine to the site of its utilization. Iron is stored in the body in the form of ferritin and hemosiderin.

Transport of iron across the placenta : The transport of iron across placenta occurs against a gradient, thereby protecting fetus against iron deficiency. However, this effective fetal parasitism is limited in cases of severe maternal iron deficiency. Thus babies with low iron stores may be born to mothers who are severely iron deficient during pregnancy. It is important to remember that most of the placental transfer of the iron occurs during the 3rd trimester of pregnancy. As a consequence of this, all preterm babies invariably develop anemia unless supplemented by iron and conversely iron deficiency in the mother may cause preterm labor.

Pica : It is a well-documented symptom but unexplainable. Pica is a habitual ingestion of unusual substances, the most common of which is eating mud or clay ( Geophagia ), laundry starch ( amylophagia ) and ice ( pagophagia ). Pica usually is the manifestation of iron deficiency and is relieved when condition is treated. Clay can behave in the gut as an exchange resin and can interfere with iron absorption.

Changes in Epithelial cells : These include koilonychia, platynychia, angular stomatitis, atrophic glossitis and mucosal changes in the stomach and small bowel leading to mucosal web as seen in Plummer Wilson syndrome, Patterson Kelly syndrome which are rare in children.

Growth retardation : There is a marked reduction in weight in iron deficient children, thought height seems to be unaffected.

Exercise intolerance : Maximum work capacity, work output and endurance are impaired in iron deficiency state. This is due to reduction in the mitochondrial enzyme - alpha glycophosphatase dehydrogenase besides anemia. Study in Indonesia demonstrated a correlation between the work output of latex tapper and hemoglobin concentration. Work output was significantly less (19%) from tappers with iron deficiency anemia than from non-anemic tappers. Similarly, another study found a significant decrease in the area of the ground cleared of weeds by anemic laborers as compared with their non-anemic counterparts.

The study done at Sri Lanka demonstrated a significantly smaller work output by anemic tea-pickers. In some of the studies, work output increased significantly following correction of anemia by administration of iron.

Behavioral changes : Theses changes occur due to diminished activity of aldehyde oxidase, required for serotonin catabolism, thus leading to increased levels of serotonin and 6 - hydroxyindole compounds. MAO which is also required for catabolism of catecholamine is also reduced. Reduced attention span, irritability, decreased scholastic performance, poor academic achievement and conduct disorders occur in these iron deficient children.

In Egypt and Java, deficiency in the mental performance of school children were reversible with the treatment. They have shown in their study that intravenous iron administration reverses low scores of cognitive function even before hemoglobin rises. Behavior studies in Young iron deficient rats, before and after iron replacement, have shown that rats are less responsive to environmental stimuli when iron deficient.

In a study of iron deficiency in the rat, depletion of total non-haem iron and ferritin iron in the brain established shortly after the time of weaning, could not be reversed inspite of continuous supply of iron from that time until adult life. Study done by Dalmann et al have shown lower mental and psychomotor development index score significantly lower than control infants. Anemic infants failed specifically in language capabilities, body balance, co-ordination skills when compared with control. Iron deficiency affect attention span and memory control rather than information processing and retrieval. Webb and Oski also have found poor scholastic performance in anemic students. Gopaldas & associates noted substantial improvement in cognitive function in anemic children after treatment with iron.

Lokeshwar et al in their study of 36 children between the age group of 6 months to 18 months, demonstrated impairment of cognitive function in iron deficient children and there was significant improvement in MDI (Mental Development Index) and PDI (Psychomotor Development Index) after iron therapy.

Altered host response : Iron deficiency affects both cell mediated as well as humoral immunity, though phagocytic activity may be normal. Killing of E.coli and Staph. Aureus is reduced. In contrast, some studies state that immunity is enhanced in iron deficient state. This is due to increased unsaturated transferrin which inhibits bacterial growth and hence high dose IV iron therapy could be harmful in such cases. However oral iron therapy only minimally changes saturation of transferrin and hence practically it does not have any adverse effect on incidence of infection. In several studies, results show that infants who receive iron supplementary formulae have fewer episodes of respiratory and gastrointestinal infections than those who receive unsupplemented formula.