The Long Road Back: Building Better Bones – Vitamin D as a Hormone

By | April 18, 2014

Calcitriol is the most active form of vitamin D and also the form that seem to function as a hormone.

Calcitriol is the most active form of vitamin D and also the form that seem to function as a hormone.

Another factor militating against classification as a vitamin is that the majority of the circulating vitamin D is relatively speaking inactive. It undergoes a two-step activation process first to calcidiol by hydroxylation at the 25 position in the liver and then to calcitriol by hydroxylation at the 1 position by the proximal tubular cells in the kidney. This is one of the reasons that osteoporosis is such a problem in patients with kidney failure and why supplementation with normal vitamin D is so ineffective in theses patients. With the modern availability of synthetic calcitriol preparations osteoporosis in these patients has become somewhat more manageable. Not only is calcitriol effective in controlling bone metabolism it has been shown to be important in preventing certain types of cancer and in modulating the immune system. One of the things that worry me about administering large amounts of exogenous vitamin D to the patients at Schlesinger Pain Centers is the possibility of upsetting calcitriol’s role as a messenger.


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