Response of biochemical markers of bone turnover to estrogen treatment in post-menopausal women: evidence against an early anabolic effect on bone formation.

Bone loss following menopause can be prevented or reduced by estrogen replacement therapy (ERT). The primary action of estrogen on bone is generally considered to be antiresorptive, but some evidence would also suggest a stimulatory effect on bone formation. The aim of this study was to assess the effect of ERT on biochemical markers of bone resorption (urinary pyridinoline and deoxypyridinoline), and of bone formation (bone-specific alkaline phosphatase--B-ALP, and the C-terminal propeptide of type I collagen--CICP) in a group of 25 postmenopausal women with no evidence of osteoporosis. Since the suggested anabolic effect of estrogen seems to take place in the early period of ERT, we measured the response of markers immediately before and after the start of treatment (30, 60, 120 and 180 days). The markers of bone resorption started to decrease at 30 days and remained low thereafter. We also observed a similar decrease in serum levels of B-ALP and CICP, reflecting a reduction of bone formation rate. Our data would indicate that ERT at the given dose does not have early anabolic effects on bone, in addition to its recognized suppressive effect on bone resorption.