Effect of oral contraceptives on the plasma concentration of pyridoxal phosphate

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Abstract
The use of oral contraceptive agents (OCA) produces biochemical abnormalities suggestive of vitamin B6 deficiency. To further define this interaction, the plasma levels of pyridoxal phosphate (PLP), the coenzyme form of vitamin B6, in 55 women who had been on OCA for 6 months or longer were compared with those of 77 nonusers. The mean plasma PLP level of OCA users, particularly that in the 25- to 34-year age group, was significantly lower than that of their age-matched controls. Twenty percent of the subjects, 20 to 34 years old, exhibited levels of less than 5 ng/ml, the lowest value encountered in control subjects of comparable age. Ten other subjects were followed prospectively from 2 weeks before OCA therapy for 4 months or longer. Significant decreases in plasma PLP were observed in nine of these subjects within the first 3 months of OCA use. However, these changes returned towards pretreatment levels in most of the subjects by the 6th month. Comparison of plasma PLP concentrations with tryptophan load tests in 15 OCA users revealed that the incidence of abnormal xanthurenic acid excretion was disproportionately high. These data are consistent with the view that OCA induces an increased requirement for vitamin B6. Although the majority of the OCA users can, in large measure, correct the relative deficiency state naturally, a substantial number remain deficient, suggesting the need for vitamin B6 supplementation in at least these individuals.

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