Iron deficient anaemia has been reasonably well characterised in the nutritional literature. The best known role for iron in humans is as part of the haemoglobin molecule in the transportation of oxygen. The pivotal role played by iron in the transport of oxygen to tissues explains some of the symptoms of iron deficient anaemia, which include tiredness, shortness of breath, pale colour and low body temperature. However, as well as this more traditional role, iron also has other important functions within the body. In particular, iron is able to act as a cofactor to certain enzymes including tyrosine hydroxylase, the enzyme responsible for the conversion of L-tyrosine to L-DOPA. Iron therefore plays a pivotal role in the dopaminergic pathway and in this way can have an influence of the production of noradrenaline, adrenaline and dopamine. The influence of iron in the dopaminergic pathway is particularly important as tyrosine hydroxylase is the rate limiting enzyme and therefore is the controlling point for production of the catecholamines.
The associations between serum ferritin, serum iron and cognition have been assessed in healthy university students1. Using electroencephalograms (EEG) traces, the authors reported a positive association between serum ferritin levels and activation of the left hemisphere relative to the right. The iron status of the students was significantly positively associated with word fluency task and inversely associated with the tonal memory backward task. The authors suggests that the ability on these task was consistent with the asymmetry seen on the EEG trace. Therefore poor iron status may affect the brain of otherwise healthy individuals, but this effects is different in particular parts of the brain. However, as none of the subjects in this study were iron deficient, it is unclear if these effects may be magnified when iron stores are depleted further. The activation of the left hemisphere of the brain by higher iron store is interesting because some evidence suggests that the dopaminergic pathways are particularly abundant in the left hemisphere.
These results are consistent with the hypothesis that iron is required for correct brain function because of its involvement in the dopaminergic pathways. Iron deficiency is known to lower the cognitive ability of sufferer and animal experiments suggests that this might result partly from impairment of the dopaminergic pathways in the brain. These dopaminergic pathways have high concentrations of iron within them, and iron deficiency may therefore decrease metabolic flux and cause reductions in catecholamine levels through decreased activity in tyrosine hydroxylase. Alternative explanations have been suggested including evidence showing that absorption of iron can reduce absorption of known neurotoxins such as lead. The ability of dopamine antagonist to preferentially affect the left hemisphere suggests that dopaminergic pathways are consistent with iron producing a preferentially left-lateralised effect in the brain. The differential effects of iron deficiency can therefore be explained by its unequal influence on these dopamine pathways.
