HORMONE REPLACEMENT THERAPY INCREASES SERUM 1,25-DIHYDROXYVITAMIN-D -A 2-YEAR PROSPECTIVE-STUDY

Osteoporosis is a common disorder in postmenopausal women, which is pr obably due to decreased ovarian function. Currently, hormone replaceme nt therapy (HRT), involving administration of estrogen and progestogen , is successfully applied to reduce bone resorption. We studied the ef fect of HRT on 23 postmenopausal women. This consisted of a combinatio n of 17 beta-estradiol and dydrogesterone, on the serum level of 1,25- dihydroxyvitamin D (1,25(OH)(2)D) after 0, 6, 12, and 24 months. We fo und mean serum concentrations (+/-SD) of 1,25(OH)(2)D of 130.5 pmol/li ter (46.1), 152.7 pmol/liter (45.1), 170.8 pmol/liter (64.0), and 155. 2 pmol/liter (59.7), respectively. The baseline values in these women were found to be significantly lower than those during therapy (P less than or equal to 0.005). No statistically significant differences wer e observed when comparing the estrogen-only phase with the combined es trogen-progestogen phase. It is concluded that HRT results in an incre ase in the serum 1,25(OH)(2)D concentration which lasts for at least 2 years. This increase may partly explain the preventive effect of HRT on osteoporosis. Furthermore, these results suggest that dydrogesteron e does not influence the estrogen-induced changes in serum 1,25(OH)(2) D concentration.