FoIlc Acid Deficiency Folic acid deficiency, the most common nutrient deficiency, may be found in over one-quarter of hospitalized psychiatric patients.' It appears to affect mood by impairing the synthesis of tetrahydrobiopterin (BH4), a cofactor essential for the synthesis of serotonin and other monoamines involved in the pathogenesis of affective disorders.^ One study found that lower plasma...