American Journal of Clinical Nutrition, Vol 27, 797-805, Copyright © 1974 by The American Society for Clinical Nutrition, Inc.

Vitamin B₆ metabolism in women using oral contraceptives

¹ From the Department of Foods and Nutrition, Oregon State University, Corvallis, Oregon 97331

To study the effect of oral contraceptives on the metabolism of vitamin B₆, three women who use these drugs ("users") and two who do not use them ("nonusers") were fed a constant diet containing 1.9 mg vitamin B₆ for 11 days. The users not only excreted elevated amounts of kynurenine-pathway metabolites in response to 2 g l-tryptophan but also excreted approximately 30% less urinary vitamin B₆ than the nonusers. Blood vitamin B₆ was only slightly lower in the users. Both groups excreted similar amounts of 4-pyridoxic acid. Results obtained from giving the tryptophan load test at different times of the day and when the users had discontinued taking the contraceptive for the menses interval emphasize the importance of giving this test dose at the same time of day and during the time the women are taking the drug.