Effects of oral contraceptives on vitamin metabolism.

PIP: Literature on the effects of oral contraceptives (OCs) on vitamin metabolism is reviewed. OCs have been reported to markedly increase serum levels of Vitamin-A. OCs may induce a thiamine deficiency and lower levels of Vitamin-B2. Concentrations of ascorbic acid in platelets, white cells, plasma, and urine are decreased by OCs. Decreased plasma and red blood cell concentrations of folic acid have been reported in OC users, though it does not appear that absorption of folate polyglutamate is affected. OC users may develop megaloblastic anemia because of folic acid deficiency. OCs have been reported to markedly reduce serum levels of Vitamin-B12. Some OC users who excrete abnormal amounts of tryptophan metabolites have some degree of true Vitamin-B6 deficiency. Evidence of altered tryptophan metabolism and/or absolute Vitamin-B6 deficiency has been found in emotionally depressed women taking OCs. OCs, especially estrogens, produce tryptophan metabolism abnormalities in the great majority of users. An effect of OCs on alpha-tocopherol plasma concentrations has yet to be demonstrated in humans.^ieng