Michael Holick's opinion matters.
- Dr. Holick discovered the mechanism for how vitamin D is made in the skin. He identified the major circulating form of vitamin D3 in human blood (calcidiol also known as 25-hydroxyvitamin D3 or 25(OH)D3. This is the form that's measured to determine deficiency states.)
- He was the first person to isolate and identify the active form of vitamin D (1,25-dihydroxyvitamin D3).
- He's authored over 300 peer-reviewed articles, 200 reviews, several book chapters, and edited 10 books.
- He's the author of The UV Advantage and the soon-to-be-released The Vitamin D Solution.
Vitamin D3, also known as cholecalciferol, is derived from animals (notably sheep's wool).
In his study...
Vitamin D2 Is As Effective As Vitamin D3 In Maintaining Circulating Concentrations Of 25-Hydroxyvitamin D, Journal of Clinical Endocrinology & Metabolism, March 2008
Dr. Holick and his colleagues gave participants one of the following daily for 11 weeks at the end of the winter in Boston:
- 1000 IU vitamin D2
- 1000 IU vitamin D3
- Combination of 500 IU vitamin D2 and 500 IU vitamin D3
"The rise in the total 25(OH)D was identical to that observed for the groups who received either 1000 IU vitamin D2 or 1000 IU vitamin D3."
"That, to me, proves that vitamin D2 is as effective as vitamin D3 in raising and maintaining 25-hydroxyvitamin D levels. That is consistent with the early literature that showed that 100 IU of vitamin D2 was effective in preventing rickets in children."1