The vitamin B6 requirement in oral contraceptive users II. Assessment by tryptophan metabolites, vitamin B6, and pyridoxic acid levels in urine

Abstract

Data were obtained from seven college-age women who used estrogen-containing oral contraceptives and who volunteered to participate in a metabolic study to investigate the requirement for vitamin B6. They consumed a basal diet containing 0.36 mg/day of the vitamin for 42 days. During the first 10 days (predepletion period) the diet was supplemented with pyridoxine hydrochloride to bring the total intake to 2.06 mg/day. After 32 days of depletion the diet was supplemented with pyridoxine hydrochloride for a daily intake of 0.96, 1.56, and 5.06 mg for 8, 9, and 7 days, respectively. Complete 24-hr urine collections were made and composited. Urine was analyzed for total vitamin B6 and 4-pyridoxic acid; and for kynurenine, 3-hydroxykynurenine, kynurenic and xanthurenic acid levels both, before and after 2 g loading doses of l-tryptophan. Results were compared with data obtained from non-oral contraceptive users who consumed a similar diet. Tryptophan metabolites significantly increased during the depletion phase and rapidly decreased with pyridoxine hydrochloride supplementation. A vitamin B6 intake of 1.56 mg/day was sufficient to restore all metabolites to original levels in oral contraceptive users. Urinary vitamin B6 and 4-pyridoxic acid levels decreased during depletion and were returned to original levels with 1.56 mg/day. An intake of 5.06 mg caused large amounts of each to be lost in the urine. The data obtained suggest that 0.96 mg was not adequate to meet the needs of oral contraceptive users as predepletion levels of most parameters studied had not yet been reached. An intake of 1.56 mg restored levels in almost all subjects and 5.06 mg caused large amounts of vitamin B6 and 4-pyridoxic acid to be excreted. An intake of 1.5 mg is similar to the previously suggested intake for nonusers.