Vitamin D metabolism in osteoporotic women during treatment with estrogen, an anabolic steroid, or calcitonin.

We assessed the effects of a continuous oral combination of estradiol and norethisterone acetate, nandrolone decanoate, or salmon calcitonin on the vitamin D endocrine system. One hundred and nineteen postmenopausal women, aged 55-75 years, with at least one osteoporotic fracture, were randomly allocated to one year of treatment with estradiol and norethisterone acetate, nandrolone decanoate, or calcitonin, all drugs with a beneficial effect on bone. All three trials were double-blind and placebo-controlled; 104 women (87%) completed the study. We measured the total serum concentration of 1,25-dihydroxyvitamin D (1,25(OH)2D) and vitamin D-binding protein, and estimated the free 1,25(OH)2D index and the "24-hydroxylase activity" initially, and at 6 and 12 months. Furthermore, the 24-h urinary excretions of calcium, phosphate, and adenosine 3'-5'-cyclic monophosphate were assessed initially and at 12 months. The serum concentration of vitamin D-binding protein and 1,25(OH)2D increased transiently during estradiol and norethisterone acetate treatment and vitamin D-binding protein decreased transiently during nandrolone decanoate treatment. None of the other parameters were significantly affected by any of the three treatments. The risk of type II errors was below 10 per cent for all vitamin D measurements. We conclude that the vitamin D metabolites are unlikely to be of major importance for the mechanism by which these drugs exert their positive skeletal effects.