Serum vitamin B₆ in schizophrenic and schizoaffective patients with and without tardive dyskinesia

There are several reports regarding the efficacy of vitamin B₆ in the treatment of tardive dyskinesia (TD). Vitamin B₆ plays a key role in the synthesis of several neurotransmitters, including serotonin, dopamine, norepinephrine, and gammaaminobutyric acid, all of which have been proposed to be involved in the development of TD. The purpose of this study was to examine whether there are special markers to distinguish long-term neuroleptic exposure patients who have TD from those patients who do not develop this side effect. In view of the pivotal role of vitamin B₆ in the synthesis of all neurotransmitters believed to take part in the pathogenesis of TD, we decided to examine whether basal levels of vitamin B₆ might explain the difference between these two groups. Such a finding could provide a predictive marker for vulnerable patients. The active metabolite of vitamin B₆ is pyridoxal phosphate (PP). Pyridoxal phosphate blood levels were measured in 15 schizophrenic and schizoaffective patients with TD and compared with 15 patients without evidence of TD (matched by sex, age, smoking, and diagnosis). We found that, although patients in the TD group were exposed to neuroleptic drugs for significantly longer periods of time, there were no differences in serum PP levels between the groups. The reports of the effectiveness of vitamin B₆ supplementation in the treatment of TD could therefore be explained by the assumption that central nervous system or intracellular vitamin B₆ levels, which are involved in the pathogenesis of TD, are not the same as vitamin B₆ peripheral serum levels. There is need for further studies, which will clarify the relationship between vitamin B₆ and TD.