Cobalamin (vitamin B12) has been implicated in the pathogenesis of several neuropsychiatric disorders. A review of 19 patients (14 vegetarians) with detectable vitamin B12 deficiency showed a variety of psychiatric symptomatology, with the majority having no significant hematologic or neurologic manifestations. Psychosis was diagnosed in a large number of our cases.
Vitamin B12 Levels and Psychiatric Symptomatology: A Case Series.