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Differences between vitamin D1 / D3 and the vitamin D that is prescribed

There is a differences in the units, but what I really want to know is the differences in the chemistry and the indications. I know vitamin D helps preserve the calcium in bones, but what other indications are for the different types of vitamin D?

Medically reviewed by Last updated on Apr 18, 2019.

Official Answer


The term "Vitamin D" now refers to several different forms. The two forms important in humans are : ergocalciferol (vitamin D2) and cholecalciferol (vitamin D3). Vitamin D2 is a synthetic form (man made) and Vitamin D3 is the internal form that we make.

German researcher Adolf Windaus first discovered 3 forms of vitamin D, which he called D1, D2, and D3. It was later learned that the vitamin D1 was a mixture of compounds rather than a pure vitamin D product, so the term D1 is no longer used.

For more information see Vitamin D -

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