Effects of oestrogen and progestogen therapy on calcium metabolism in post-menopausal women.

Abstract

The effects of estrogen therapy on calcium metabolism was studied in postmenopausal women. Ethinyl estradiol gradually decreases plasma and urinary calcium and phosphate levels reaching a maximum at about 6 months. This decline is partially reversed by the end of 1 year though values consistently and indefinitely remain lower than control values. Tubular reabsorption of phosphate also shows a similar pattern. Urine calcium levels fall earlier than urine hydroxyproline though bo th appear to remain within the premonpausal range indefinitely. The hyp ophosphatalmic effect of estrogens is in part due to an inhibition of bone resorption but appears primarily due to parathyroid stimulation. The rise in calcium absorption may be explained by the rise in parathyroid hormone. Since the reduction in the rate of new bone formation is not as great as the degree of inhibition of bone resorption the net long-term effect is an enhancement of bone calcium balance. However there is no evidence that estrogens directly stimulate new bone formation. It is not certain to what extent the incidence of forearm fracture spinal osteoporosis and fractured femur of the neck might be reduced by the inhibition of bone resorption nor is it known how estrogens inhibit bone resorption. The comparative doses of estrogen needed to significantly reduce urine calcium excretion at 1 month are 6 mg estriol succinate .025 mg ethinyl estradiol .1 mg estrone sulphate and .65 mg conjugated estrogens. The results indicate that estrogens are capable of inhibiting bone resorption in postmenopausal women for most likely an indefinite period of time.