Understanding Vitamin D…Part 1

There are two kinds of Vitamin D that we can take or get from foods, those are known as D2 and D3.  A number of years ago a study was done on how well we absorb D2 and D3 and it was found that we absorb D3 slightly better than we do D2[1].  This led to a wide-spread false belief that D3 is better for us than D2.  Now most people would not have any problem with that assumption, however, if you happened to be a vegetarian then the commonly held belief might cause you to do a double take because D2 comes from plant sources whereas D3 comes from animal sources and we are only talking about a slight absorption difference.  Unfortunately, that false belief from a decade ago has led to an even more false belief that D2 is somehow not-active and D3 is active which is completely (sorry folks) false on its face.  However, in order to understand just how untrue and uninformed this belief is, you’d have to know a thing or two about Vitamin D which we will cover in this article. 

 

Vitamin D is synthesized, or “created,” by animals and some plants in response to the sun’s light and, upon its creation, then goes through a multi-stepped process in order to be used.  Vitamin D2’s true chemical name is Ergocalciferol, and Vitamin D3 is, Cholecalciferol, and I invite you to check the labels on your own Vitamin D bottles (or those at the store) in order to personally verify that your Vitamin D2 is truly “Ergocalciferol,” and your Vitamin D3 is truly “Cholecalciferol.”  You see, this is an important distinction that many well-meaning exerts (including researchers and well-loved doctors) make that perpetuates the false belief that either of these are in “active” form. 
 

 



So now that you know that Vitamin D3 is, in fact, Cholecalciferol, the next step is understanding how the body utilizes Cholecalciferol.  However, it is also important to understand that we also make Cholecalciferol.  We do that from Cholesterol (that we also make), or rather a part of it called, “7-dehydrocholesterol.”  The process takes place within the fat under our skin; in response to the UV rays from the sun or lights, we turn 7-dehydrocholesterol into Cholecalciferol.  From there, whether we make the Cholecalciferol in our skin or whether we take it as a pill or get it from foods, the Cholecalciferol enters our blood stream where it is then converted into “Calcidiol” which then finds its way into our kidneys and is converted into “Calcitriol,” the ONLY true physiologically “active” form of Vitamin D.  In other words, whether we make it ourselves from the sun or take it as D3, it still has to go through an additional 2-step process in order for our body to use it.  Or, in still other words, in order for it to become “active.” 

 

It always shocks and disappoints me when the doctors and experts that I love and respect make this critical error in calling D3 active, and it never fails to sadden me when vegetarians are discouraged from taking D2 which, despite not being absorbed as well, is still absorbed well enough to be a viable alternative to D3 which is derived from animal sources or from irradiation.

 

I hope that helps you understand a little more about Vitamin D.  In the next part, we will take a deeper look into Vitamin D testing and the implications it has to all we think we know about Vitamin D.

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[1] Evidence that vitamin D3 increases serum 25-hydroxyvitamin D more efficiently than does vitamin D2. H M Trang, D E Cole, L A Rubin, A Pierratos, S Siu, and R Vieth, American Journal of Clinical Nutrition October 1998 vol. 68  no. 4  854-858