Rao et al19 and Connor and Menzies20 demonstrated that iron is an essential component for the metabolism of neurotransmitters, being a cofactor for the enzymes tryptophan hydroxylase and tyrosine hydroxylase, which act, respectively, in the synthesis of serotonin and dopamine, which plays a role in the regulation of the sleep-wake cycle.21 In addition, a study demonstrated that the levels of dopamine D1 and D2 receptors were decreased in rats that had iron deficiency anemia.22 Here, TH is linked to anemia.