Abstract
Serum concentrations of 25-hydroxyvitamin D (25-OH-D) and 24, 25-dihydroxyvitamin D [24, 25-(OH) 2-D] were measured in lipid extracts of 1ml of human sera by a competitive protein binding assay. 25-OH-D and 24, 25-(OH) 2-D were isolated from the lipid extracts by Sephadex LH-20 column chromatography. The 24, 25-(OH) 2-D fraction on the Sephadex LH-20 columns were further purified by high pressure liquid chromatography prior to assay. Serum levels of 25-OH-D and 24, 25-(OH) 2-D in normal males were similar to those in normal females throughout each age group. Serum levels of 25-OH-D and 24, 25-(OH) 2-D in newborns were 8.28±1.68ng/ml (mean±SD) and 0.55±0.16ng/ml, respectively, which were significantly (p<0.001) lower than those in adults (21.3±4.8ng/ml of 25-OH-D and 1.55±0.31ng/ml of 24, 25-(OH) 2-D). A seasonal variation was demonstrated in serum levels of 24, 25-(OH) 2-D as well as those of 25-OH-D. Serum levels of 24, 25-(OH) 2-D were highly correlated (γ=0.884, p<0.001) with those of 25-OH-D in normal human subjects, and the percentage ratio of 24, 25-(OH) 2-D/25-OH-D was 7.4±1.4%(mean±SD), irrespective of age or seasonal variations.
