Vitamin B6 metabolism in users of oral contraceptive agents. I. Abnormal urinary xanthurenic acid excretion and its correction by pyridoxine

Abstract

The response of the increased urinary zanthurenic acid (XA) excretion following a 2-g L-tryptophan load to oral doses of 2 5 10 and 20 mg - pyridoxine hydrochloride was systematically studied in a group of 43 healthy women (ages 21-42) 33 of whom used oral contraceptives. Each was followed through 3 consecutive cycles. Vitamin-B-6 was administered during the first and third cycles. The middle cycle was a non-vitamin B-6-supplemented control period. None of the 10 non-oral contraceptive users excreted more than 35 mc/M of XA/8 hours. The majority of oral contraceptive users (75%) however excreted an average of 167 mcM/8 hours. The 8 hour urine collection period was found to contain a relatively contant fraction (average 63.4%) of the 24 hour XA excretion after a 2-g L-tryptophan oral load. As such it was a valid and reliable urine collection period for this index of vitamin-B-6 inadequacy. A 2 mg dose of pyridoxine hydrochloride equivalent to the Recommended Dietary Allowance (37 38) of vitamin-B-6 was sufficient to correct only 10% of the women studied following the 20 mg dose 14% remained uncorrected. It was recommended that to correct altered vitamin-B-6-tryptophan metabolism resulting from oral contraceptive usage a 30 mg dosage be prescribed. (AUTHORS MODIFIED)