Achieving optimal levels of 25-hydroxyvitamin D (25(OH)D) through diet is difficult as most foods contain low levels of vitamin D.  As such, many people resort to using supplements containing vitamin D2, vitamin D3, or 25(OH)D3 to reach adequate serum concentrations of 25(OH)D.  Long term supplementation studies have demonstrated that 25(OH)D3 is more effective at raising serum 25(OH)D concentrations than is vitamin D3.  However, none of those studies have explored the pharmacokinetics of the supplements.  Graeff-Armas and colleagues conducted a long term pharmacokinetic study and report the results of that work in the January 2020 issue of The Journal of Nutrition.

Subjects (n=91) received supplements for 6 months followed by a 6 month wash out period in the randomized, double-blind study.  Supplements contained 10, 15, or 20 µg of 25(OH)D3 or 20 µg of vitamin D3.  Serum levels of 25(OH)D were determined at multiple time points and the pharmacokinetic parameters for each individual were calculated.

There were no differences in baseline 25(OH)D among the groups.  The increases in serum 25(OH)D were higher among those in the groups receiving 25(OH)D3 than in those receiving vitamin D3.  Steady state levels were achieved quicker in those receiving 15 or 20 µg of 25(OH)D3 than in those receiving vitamin D3 and elimination after ceasing the supplement was also higher in those receiving 25(OH)D3.  The data led the authors to conclude that 25(OH)D3 was 3 times more effective than vitamin D3 at raising 25(OH)D serum concentrations.

References Graeff-Armas LA, Bendik I, Kunz I, Schoop R, Hull S, Beck M. Supplemental 25-hydroxycholecalciferol is more effective than cholecalciferol in raising serum 25-hydroxyvitamin D concentrations in older adults.  Journal of Nutrition, DOI:

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