Effect of vitamin B-6 deficiency on fasting plasma homocysteine concentrations

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Abstract
The catabolism of homocysteine through cystathionine synthesis requires pyridoxal-5′-phosphate, thus the effect of vitamin B-6 deficiency on plasma homocysteine concentrations was evaluated. Total fasting plasma homocysteine concentrations were measured in 11 elderly subjects aged 64.4 ± 1.7 y (x̄ ± SE) who consumed a vitamin B-6-deficient diet for ≤ 20 d. Only 1 of the 11 subjects was found to have elevated homocysteine concentrations even though all subjects exhibited high urinary xanthurenic acid concentrations after a tryptophan load, a measure indicative of vitamin B-6 deficiency. In a supporting study, fasting plasma homocysteine concentrations were measured in 3- and 23-mo-old rats fed vitamin B-6-deficient diets and were compared with those of vitamin B-6-replete, pairfed controls. There was no difference in homocysteine concentrations between deficient and pair-fed animals after 6 wk of the dietary regimen for either age group; after 9 wk a modest elevation was observed in the 3-mo-old deficient rats whereas no difference was observed for the 23-mo-old rats. It is concluded that fasting plasma homocysteine concentrations are not initially elevated in vitamin B-6 deficiency and therefore fasting plasma homocysteine concentrations are not a good indicator of vitamin B-6 status.