Ability of 25-hydroxyvitamin D₃ therapy to augment serum 1, 25- and 24, 25-dihydroxyvitamin D in postmenopausal osteoporosis

Six women (mean age, 62 yr; range, 48-77 yr) who were considered to have postmenopausal osteoporosis, as demonstrated by radiological evidence of vertebral crush fractures, low intestinal calcium (Ca) absorption, and bone biopsies consistent with this diagnosis, received a pharmacological dose of 25-hydroxyvitamin D₃ (25OHD₃; 20 μg/day) for 3 months. This treatment increased the serum concentration of 25OHD from 8.7 ± 4.6 to 30.2 ± 9.5 (SD) ng/ml (P < 0.0025), increased the serum concentration of 24, 25-dihydroxyvitamin D from 1.2 ± 1.2 to 7.7 ± 2.7 ng/ml (P < 0.025) in three patients, and increased the serum concentration of 1, 25-dihydroxyvitamin D from 2.1 ± 1.7 to 4.3 ± 1.5 ng/dl (P < 0.025). Moreover, there were commensurate increases in fractional intestinal Ca absorption from 0.38 ± 0.03 to 0.49 ± 0.06 (P < 0.025) and in urinary Ca from 69 ± 31 to 127 ± 67 mg/day (P < 0.025). There were no significant changes in serum Ca (9.6 ± 0.5 vs. 9.5 ± 0.4 mg/dl), serum phosphorus (3.4 ± 0.2 vs. 3.6 ± 0.4 mg/dl) or alkaline phosphatase (87 ± 27 vs. 91 ± 30 IU/liter) before or after therapy. It is concluded that orally administered 25OHD₃ is not only effective in raising the low intestinal Ca absorption observed in postmenopausal osteoporosis but also in increasing the serum concentrations of 24, 25-dihydroxyvitamin D and 1, 25-dihydroxyvitamin D.