Vitamin B6 requirements of women using oral contraceptives

Fifteen women who used combined estrogen-progestogen oral contraceptives and nine control women were given a vitamin B6-deficient diet for 4 weeks and the same diet supplemented with 0.8, 2.0, or 20.0 mg of pyridoxine hydrochloride for an additional 4 weeks. At weekly intervals a variety of indices of vitamin B6 nutrition were measured to determine rates of depletion and repletion. The tryptophan load test (2.0 g) was significantly different in the contraceptive users. However, other indices, including urinary cystathionine (3.0 g L-methionine load), urinary 4-pyridoxic acid, plasma phosphate, and erythrocyte alanine and aspartate aminotransferases, were not significantly different. Since altered tryptophan metabolism persisted in contraceptive users even when other indices of vitamin B6 nutrition were normal, we suggest that the use of oral contraceptives specifically affects tryptophan metabolism by some means other than through a vitamin B6 deficiency.