Serum Concentrations of 1,25-Dihydroxyvitamin D2 and 1,25-Dihydroxyvitamin D3 in Response to Vitamin D2 and Vitamin D3 Supplementation

Objective: The purpose of this study was to determine 1,25-dihydroxyvitamin D-3 [1,25(OH)(2)D-3] and 1,25-dihydroxyvitamin D-2 [1,25(OH)(2)D-2] levels in healthy adults consuming 1000 IU vitamin D-2 or vitamin D-3 per day for 11 weeks. Subjects and Design: Blood from 34 healthy male and female adults, aged 18 to 79 years, from a placebo-controlled, double-blind study who received a placebo, 1000 IU vitamin D-3, or 1000 IU vitamin D-2 daily for 11 weeks at end of winter was analyzed. Serum levels of 25-hydroxyvitamin D-2, 25-hydroxyvitamin D-3, 1,25(OH)(2)D-2, and 1,25(OH)(2)D-3 were determined by liquid chromatography tandem mass spectroscopy. Results: Of the adults, 82% were vitamin D insufficient (serum 25-hydroxyvitamin D [25(OH)D < 30 ng/mL]) at the start of the study. Administration of vitamin D-2 and vitamin D-3 induced similar increases in total 25(OH)D as well as in 25-hydroxyvitamin D-2 and 25-hydroxyvitamin D-3, respectively. Compared with placebo and adjusting for baseline levels, 1000 IU daily of vitamin D-2 was associated with a mean increase of 7.4 pg/mL (95% confidence interval, 4.4 - 10.3) in 1,25(OH)(2)D-2, which was accompanied by a mean decrease of 9.9 pg/mL (-15.8 to -4.0) in 1,25(OH)(2)D-3. No such differences accompanied administration of 1000 IU daily of vitamin D-3. Conclusion: Vitamin D-2 and vitamin D-3 were effective in raising and maintaining total serum concentrations of 25(OH)D. Ingestion of vitamin D-2 also resulted in an increase in serum concentrations of 1,25(OH)(2)D-2. This increase was accompanied by a comparable decrease in serum concentrations of 1,25(OH)(2)D-3; therefore, the total 1,25-dihydroxyvitamin D [1,25(OH)(2)D] concentrations did not significantly change after 11 weeks compared with baseline levels. Ingestion of vitamin D-3 did not alter serum concentrations of 1,25(OH)(2)D-3 or total 1,25(OH)(2)D. Therefore, ingestion of 1000 IU vitamin D-2 or vitamin D-3 for 11 weeks was effective in raising total serum concentrations of 25(OH)D as well as sustaining serum concentrations of total 1,25(OH)(2)D. (J Clin Endocrinol Metab 98: 973-979, 2013)