Editor's note: Part 1 of this article appeared in the Dec. 16, 2009 issue.
Table 1: Vitamin D2 Versus Vitamin D3 (nanograms per milliliter)
|Treatment||Amount of D3||Number of Subjects||Baseline 25(OH)D||Final 25(OH)D||Increase (ng/ml)|
|D2 plus D3||500 + 500||18||20.2||28.4||8.2|
In this study, vitamin D2 and vitamin D3 equally raised serum 25(OH)D levels. Furthermore, the combination of both forms of vitamin D also showed no statistical difference. The most important aspect of this study to me was the fact that after 11 weeks of 1,000 IU daily, none of the groups reached the normal serum range of 30 ng/ml. In fact, the peak serum 25(OH)D concentrations were achieved after approximately six weeks and then leveled out for the remaining five weeks. One thousand IU/day of any form of vitamin D was not enough to raise 25(OH)D to low-normal levels, even though the dose was 2.5 times more than the RDA (400 IU).
Table 2: 25(OH)D Laboratory Measurements
|Nanograms/milliliter||ng/ml||x 2.5 = nmol/L||30-74 ng/ml||<30||<20|
|Nanomoles/liter||nmol/L||x 0.4 = ng/ml||75-85 nmol/L||<75||<50|
In the meantime, studies like this show that more evidence is needed before a blanket recommendation can be made that D2 is clearly inferior to D3. Since most supplements use D3 already, the primary concern of patients and providers should be the amount rather than the form. When a patient recently asked me, "Is it better for me to take 400 D3 instead of the 400 D2 I use now," I replied, "Instead of buying more, just take more of what you already have."
- Holick MF, Biancuzzo RM, Chen TC, et al. Vitamin D2 is as effective as vitamin D3 in maintaining circulating concentrations of 25-hydroxy vitamin D. J Clin Endocrinol Metab, 2008;93:677-81.
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