Effect of high dose ascorbic acid on vitamin B6 metabolism

The influence of ascorbic acid intake on vitamin B6 metabolism in humans was determined in three separate studies. Five subjects in study I and two subjects in study II received 0.5 ( 2 days) and 1 g (7 days) doses of L-ascorbic acid (AA), respectively, before supplementation with 2 mg of pyridoxine hydrochloride (PN-HCl). From daily diet records the percentage of the intake of vitamin B6 excreted as urinary 4-pyridoxic acid (4PA) was calculated. Because of the variability in vitamin B6 intake, study III was conducted with four male and four female subjects, who received identical meals on days 2, 3, 9, and 10 and 1 g of AA on days 4 to 10. Two milligrams of PN.HCl were given the day before and the last day of AA administration. In contrast to studies I and II, where excretion of 4PA appeared to increase on the day of PN.HCl supplementation plus AA compared to pre-AA, urinary 4PA excretion in the eight subjects of study III was not significantly different when the same PN.HCl supplemented pre-AA and post-AA days were compared. Also, the fasting plasma pyridoxal 5'-phosphate level was not significantly altered when AA was administered. It is concluded that short-term AA supplementation did not alter vitamin B6 metabolism.