What about other deficiencies? Other vitamins and nutrients? You'd expect people that are admitted to psychiatric hospitals to have more than one deficiency since they might not be able to take good care of themselves.
Off the top of my head zinc, magnesium, various forms of B-vitamins and selenium imbalances are seen in different disorders. Zinc deficiency in depression, zinc overabundance in schizophrenia. Both zinc and magnesium seem to have roles in NMDA neurotransmission. B-vitamins play a role in neurotransmitter production.