Vitamin A and oral contraception (letter)

In a readers reply to a previously-published article the effects of contraceptive estrogens on plasma vitamin A levels are discussed. Plasma vitamin A is bound to retinol binding protein (RBP) and thus reflects variations in plasma concentrations of RBP. Contraceptive estrogen doses (as well as glucocorticoids) cause important rises in plasma RBP and other transport proteins synthesized by the liver. These rises are due neither to changes in iron metabolism nor to endocrine hyperfunction. Nor is there any question of hypervitaminosis A (with attendant possibilities of birth defects) since there is no change in free non-bound vitamin A.