Menopausal changes in bone remodeling.

Bone remodeling was measured by a calcium-kinetic method in 151 normal perimenopausal women, and the effect of estrogen status on remodeling level and skeletal balance was determined. Premenopausal women exhibited remodeling rates of 0.337 gm/day Ca for mineral accretion and 0.358 gm/day Ca for mineral resorption. The difference between the two rates (computed skeletal balance) was -0.021 gm/day Ca. Postmenopausal women treated with estrogen in a mean dose of 0.0188 mg equivalents of ethinyl estradiol exhibited values for accretion and resorption (0.332 and 0.351 gm/day Ca), essentially identical with those of the premenopausal group. However, untreated postmenopausal women exhibited remodeling rates of 0.387 gm/day Ca for accretion and 0.425 gm/day Ca for resorption, with a computed skeletal balance of -0.038 gm/day Ca. These values were significantly higher than those of either the premenopausal or treated postmenopausal groups. Paired studies across menopause in 15 of the women demonstrated a rise in remodeling rates virtually identical to that estimated from the differences between groups. Estrogen loss at menopause is thus associated with an apparent partial release from an inhibition of skeletal resorption, and this release is, in whole or part, responsible for the negative skeletal balance shift associated with the postmenopausal years.