M. J. A. J. M. Hoes: The effect of pyridoxine, L-tryptophan and zincsulphate on depression and systemic L-tryptophan metabolism
Depressive patients were studied before and after four weeks of treatment.
Zung depression scale, serumcopper, 24 hours excretion in urine of 5-hydroxyindolacetic acid (5-HIAA) and 24 hours excretion in urine of xanthurenic acid (XA) after oral intake of 5 grams of L-tryptophan were measured.
Treatment consisted in pyridoxine 3 dd 125 mg (N = 10), or pyridoxine 3 dd 125 mg + L-tryptophan 2 grams vespere (N = 12), or pyridoxine 3 dd 125 mg + zincsulphate 3 dd 50 mg (N = 5). 
Before treatment Zung-score was elevated in all three groups. Serumcopper was high in the first two groups, and elevated in the third which consisted in women on oral contraceptives. The 5-HIAA excretion was normal, but the XA was elevated in all three groups. Pyridoxine resulted in significant improvement of the Zung-score (p ≤ 0,0125) and XA (p ≤ 0,05). Pyridoxine + L-tryptophan improved Zung-score more significantly (p ≤ 0,0005) and XA as much (p ≤ 0,05). Pyridoxine + zincsulphate bettered Zung-score (p ≤ 0,10), the serumcopper (p ≤ 0,05) and the XA (p ≤ 0,025). The 5- HIAA excretion rose slightly by all three treatments.
The systemic metabolic results are discussed in relation to the pathophysiology of depression. A controlled study in the antidepressant effects of pyridoxine alone or in combination is warranted on the basis of the results of this open study.