Zinc is an essential trace mineral required for a large number of biological roles, mainly as cofactors for enzymes in metabolic pathways. More than 300 enzymes are known to have a requirement for zinc, and zinc also plays a role in DNA replication, transcription and protein synthesis as well as cell division. The wide ranging role of zinc in human nutrition has been of interest to nutritionists, as low dietary intakes of zinc may cause serious health effects. What is more, evidence suggests that the zinc intake of those living in the Western nations is low and this may be causing a large number of subclinical deficiency symptoms. In particular, an adequate zinc intake may be required for correct mental function. In this regard it is known that zinc is an antagonist to the glutamate N-methyl-D-aspartate (NMDA) receptor and may exhibit antidepressant-like effects in humans and animals. Zinc therapy may therefore be a benefit to those who have depressive symptoms, particularly if they have low levels of zinc in the diet.
Zinc may inhibit the glutamate NMDA receptors in the brain, either directly, or indirectly through control of other receptors such as the metabotropic glutamate and glutamate AMPA receptors. Zinc may also inhibit glycogen synthase kinase-3β which may be involved in influencing the development of bipolar disorder. Zinc supplements have been shown to reduce depressive symptoms in human subjects.
Zinc is present in high amounts in particular parts of the brain, particularly the hippocampus and cerebral cortex. Electroshock therapy has been shown to increase zinc concentrations in the brains of rats, and the antidepressant drug impirimine is known to increase the ability of zinc to inhibit the glutamate NMDA receptor. In animal models, zinc therapy exerts antidepressant-like activity, and very low levels of certain antidepressant drugs, that would be ineffective on their own, are made clinically viable with the addition of zinc. Zinc may increase cortical and hippocampal brain derived neurotrophic factor (BDNF) and this may in term have neuroprotective and neuroregenerative effects. Depressed humans have been shown to have lower levels of zinc compared to healthy controls. In clinical studies, supplementation with zinc significantly reduced the depressive symptoms of human subjects when compared to a control, suggesting that zinc therapy for those with depression may have particular benefits to mood.
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