The effect of protein intake on the excretion of vitamin B₆, 4-pyridoxic acid, and xanthurenic acid in preadolescent boys

The effect of protein intake on vitamin B₆ status was investigated in preadolescent boys. Twelve subjects rotated through a diet sequence containing daily intakes of 1.15 mg vitamin B₆ and 29, 54, or 84 rim protein. Total vitamin B₆ and 4-pyridoxic acid were determined in urine composites from the last 5 days of a 10-day experimental period. Xanthurenic acid, following a 2 gm L-tryptophan dose, was assayed from urine collected on the last day of each experimental period.

There were significant differences found between period vitamin B₆ intakes in diets containing varying levels of dietary protein. However, vitamin B₆, 4-pyridoxic acid, and xanthurenic acid excretion was not significantly different between subjects consuming 29, 54, or 84 gm protein. The excretion of these metabolites varied from period to period for each child. Mean group data indicated that consumption of the low protein diet resulted in highest excretion of vitamin B₆ and 4-pyridoxic acid and lowest excretion of xanthurenic acid. Highest excretion of xanthurenic acid and lowest vitamin B₆ excretion were observed in response to the high protein diet. Although these excretion patterns suggested an effect of protein intake, the differences between excretion of these metabolites on the basis of protein level were not significant.

A daily intake of approximately 1.15 mg vitamin B₆ was adequate for maintenance of proper vitamin 86 nutriture for subjects consuming low, medium and high protein diets. The possible cause for the variation between groups due to the diet rotation sequence is discussed. Since the vitamin B₆ requirement - protein intake relationship has been exclusively studied in adults, suggestions for further research on this problem with preadolescent children are recommended.