Effect of oral vitamin B6 supplementation on in vitro platelet aggregation.

A randomized, double-blind study was conducted with 12 healthy adult males to determine the effects of oral pyridoxine supplementation on in vitro platelet aggregation. Following a 4-wk baseline period, half the subjects received 100 mg/day of pyridoxine X HCl while the remaining subjects received a placebo for 6 wk. In vitro platelet responses to ADP and collagen and the plasma pyridoxal 5'-phosphate (PLP) concentrations were measured at biweekly intervals. Plasma PLP concentrations increased significantly (p less than 0.001) for those receiving the vitamin B6 compared to baseline values or compared to those receiving the placebo. However, there was no significant effect of increased levels of plasma PLP on collagen-stimulated platelet aggregation and only a slight effect on ADP-stimulated aggregation. Acute administration of 100 mg pyridoxine X HCl failed to alter the in vitro response of platelets to either ADP or collagen. Reevaluation of conclusions based solely on in vitro studies suggesting the use of pyridoxine as an effective in vivo antithrombotic agent may be warranted.