You May Make Enough D, But What Did the Discovery of Vitamin D Teach Us About Provitamin D

Vitamins were discovered many years ago. The debilitating disease of Rickets mid 1600s described by Whistler and Glisson and the condition of bone pains, fractures, and muscle weakness are both now known to be the cause of very low vitamin D.  Vitamin D is unique as it can be produced by the body subcutaneously after exposure to ultraviolet B radiation. It is also unique in other ways as they have discovered receptors for this vitamin all over our body, making it one of the most active hormones we have. By 1918, Sir Edward Mellanby discovered the micro-nutrient lacking in cases of rickets was something that was soluble in fat which was the clue that lead to Goldblatt and Soames to link this to a compound in the skin, which in turn led to the discovery of the chemical structure of vitamin D by Windaus. Oddly, the discovery of Vitamin D followed the physiologic course the molecules encounters in our bodies. It has to do with what has now become the principle of provitamin and previtamins. And I’m adding a bit of philosophy of my own to the Whistler-Glisson-Mellanby-Goldblatt-Soames-Windaus compound's elucidation! The two main types of Vitamin D are D2 and D3. You skin makes Provitamin D3 , it’s the most primitive form of the vitamin D3, it cannot be vitamin D3 and it is not directly converted to vitamin D3. Within the skin the provitamin D3 is converted to previtamin D3 which is then converted in the liver to actual Vitamin D3 also called 25-hydroxyvitamin D3. Interestingly this is not the active form of the vitamin D3. Active vitamin D3 is 1,25-hydroxyvitamin D3, which is made by the kidney. It is actually what is called calcitriol. Or as I like to think of it as “post-vitamin D3” reminding me that it is made next in the physiologic cascade!

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