Oral contraceptives and bone metabolism.

In women, the bone metabolism is markedly influenced by gonadal steroids and by their fluctuations. Indeed, estrogens influence bone metabolism by influencing endocrine and paracrine functions involved in bone remodelling. In normally cycling women, the administration of oral contraceptives does not increase bone mineral density and does not induce deleterious effects on bone. In women with ovulatory disturbances, bone turnover is increased and bone mineral density is lower than in normally cycling women. In these cases, administration of oral contraceptives is capable of blocking increased bone loss and of restoring a normal bone mineral density. Similarly, in women treated with gonadotropin releasing hormone (GnRH) analogs, the concomitant administration of oral contraceptives completely antagonizes GnRH analog-induced bone loss. The progestogenic component of oral contraceptives seems to contribute to the protective effect of estrogens on bone. Oral contraceptives are safe for bone maintenance in normal adult women, and are indeed indicated to prevent postmenopausal osteoporosis in women with ovulatory disturbances.