Relationship of dietary tryptophan and niacin to tryptophan metabolism in schizophrenics and nonschizophrenics

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Abstract
Calculated 24-hr dietary intakes of tryptophan and niacin were statistically correlated with 24-hr urinary excretions of nine metabolites of tryptophan. Comparisons were made of the correlations between a group of schizophrenics and nonschizophrenics. Results revealed that a positive significant correlation existed between xanthurenic acid (XA) and kynurenic acid (KA) values and tryptophan ingestion in nonschizophrenics. but not in schizophrenics. Niacin ingestion was positively correlated with XA, KA, and 5-hydroxyindoleacetic acid (5-HIAA), the urinary metabolite derived through the indole pathway involving serotonin, in nonschizophrenics, but not in schizophrenics. 5-HIAA was found to be positively correlated with XA and KA in both schizophrenics and nonschizophrenics. Discussion included the suggestions that: 1) there is a control mechanism which determines the amount of trptophan metabolized by the indole and/or kynurenine pathways which schizophrenics lack; 2) tryptophan hydroxylase and/or pyrrolase may exert the control and should be studied in schizophrenics; 3) dietary manipulation will not affect tryptophan metabolism in schizophrenics; and 4) pyridoxine deficiency is not involved.