Plasma profile of hydroxylated vitamin D metabolites: methods and results in normals for spring-winter in Southern Finland.

The spring-winter plasma concentrations of the hydroxylated metabolites of vitamin D have been measured in normal human subjects (20 male, 13 female), using high pressure liquid chromatography with UV-detection for 25-hydroxy vitamin D3/D2 (25(OH)D) and 24,25-dihydroxy vitamin D3/D2 (24,25(OH)2D) and a radioligand receptor assay for 1,25-dihydroxy vitamin D3/D2 (1,25-(OH)2D). The respective levels were 26.6 +/- 16 nmol . l-1, 2.24 +/- 1.3 nmol . l-1 and 114 +/- 35 pmol . l-1. These are in good agreement with levels from other centres for the same season. There was a significant negative correlation between 24,25(OH)2D and 1,25(OH)2 levels. The possible significance of this in the context of the low post-winter body burden of vitamin D is discussed. There was a positive correlation between 25(OH)D and 24,25(OH)2D levels but it did not reach statistical significance. There were no statistically significant differences between the levels of the hydroxylated metabolites in men and women but the 24,25(OH)2D levels were generally lower in the women. The 1,25(OH)2D levels were similar to those measured by isotope dilution mass fragmentography on Norwegian donor blood.