Serum 1,25-dihydroxyvitamin D in normal subjects and in patients with postmenopausal osteopenia. Influence of age, renal function and oestrogen therapy.

: The serum concentrations of 1,25-dihydroxyvitamin D (1,25-(OH)2D) were measured in 194 healthy subjects aged 15-90 years. The mean level was 32.8 +/- 12.5 pg/ml (SD) without age-dependent changes. The mean serum concentration was reduced (26.9 +/- 13.6 pg/ml) in 55 patients with postmenopausal osteopenia compared to 62 non-osteopenic age-matched controls (32.8 +/- 11.6 pg/ml) (p less than 0.02). The serum concentrations correlated positively with the creatinine clearances in 23 osteopenic patients studied. Treatment with oestradiol increased serum 1,25-(OH)2D significantly in postmenopausal women. A reduced production of 1,25-(OH)2D or a reduced sensitivity to this hormone may play a significant role in the pathogenesis of postmenopausal osteopenia.