Inter-individual differences in pharmacokinetics of vitamin B6: A possible explanation of different sensitivity to its neuropathic effects

The use of vitamin B6 supplements has gained lots of attention over the past years as they have been related to the development of peripheral neuropathy. The present study focused on the pharmacokinetics of vitamin B6. Twelve healthy volunteers were daily supplemented with either 50 mg pyridoxine or pyridoxal-phosphate for one week. On days 1, 3 and 7, blood samples were taken after oral intake of the supplements. Plasma levels of different vitamers of B6 were determined with ultra-performance liquid chromatography-tandem mass spectrometry. Additionally, reported adverse reactions related to polyneuropathy and vitamin B6 supplements were analyzed. At day 1, pyridoxine only increased after supplementation with pyridoxine during the 4 h analysis. At days 3 and 7, average plasma pyridoxal-phosphate and pyridoxal concentrations significantly increased after supplementation with both vitamers. Average plasma pyridoxine concentrations only significantly increased after 3 and 7 days of supplementation with pyridoxine. Large individual differences in plasma levels of B6 vitamers were seen at all days. Also, individual differences concerning dose and plasma levels were determined in the reported complaints. Our results show that there is a clear inter-individual difference in kinetics of vitamin B6, potentially explaining differences in sensitivity to vitamin B6 toxicity.