Vitamin D
What is Vitamin D?
Vitamin D is not a vitamin but a hormone. A hormone is a substance that our body produces. After its synthesis, a hormone is released into the blood circulation. Then it reaches many distant organs and exerts its medical effects.
Vitamin D-a Hormone
Vitamin D is
produced in the skin from 7-dehydrocholesterol (pro-vitamin D3) which is
derived from cholesterol. Here is evidence that cholesterol is not all
bad, contrary to what most people think these days. The fact is that
cholesterol is a precursor for most hormones in your body.
Type B Ultraviolet
rays (UVB) from the sun act on pro-vitamin D3 and convert it into
pre-vitamin D3, which is then converted into vitamin D3. Medically
speaking, we call it cholecalciferol. Vitamin D3 then leaves the skin
and gets into the blood stream where it is carried on a special protein
called a vitamin D-binding protein.
Through blood circulation, vitamin D3 reaches various
organs in the body. In the liver, vitamin D3 undergoes a slight change
in its chemical structure. At that point, it is called 25, hydroxy
cholecalciferol or 25 (OH) Vitamin D3 (or calcidiol).
It is then carried through the blood stream to the kidneys where
it goes through another change in its chemical structure. At that point,
it is called 1,25 dihydroxy cholecalciferol or 1,25 (OH)2
vitamin D3 (or calcitriol) . This is the active form of vitamin D. It
gets in the blood stream and goes to various parts of the body and
exerts its actions. That is why vitamin D is really a hormone.
With the discovery
that vitamin D is a hormone, scientists found the main effect of vitamin
D was on calcium and phosphorus absorption from the intestines.
It was also realized that people with kidney failure
cannot convert 25 (OH) vitamin D into 1,25 (OH)2 vitamin D.
Therefore, people with chronic kidney failure on dialysis were placed on
a synthetic supplements of 1,25 (OH)2 vitamin D which is also
called calcitriol. Drug companies saw an opportunity and started
manufacturing calcitriol (brand name Rocaltrol). Soon, it became a
standard of medical practice to prescribe calcitriol to every patient on
chronic kidney dialysis.
For most physicians, this is
where their knowledge of vitamin D ends.
In the last couple of decades, researchers discovered that vitamin D is not only involved in the absorption of calcium and phosphorus from the intestines, but also plays an important role in the normal functioning of every system in the body
An Epidemic of Vitamin D deficiency
Test to Diagnose Vitamin D deficiency
Treatment of Vitamin D deficiency
This article was written by Sarfraz Zaidi, MD, FACE. Dr. Zaidi
specializes in Diabetes,
Endocrinology
and Metabolism.
Dr. Zaidi is a former Assistant Clinical Professor of Medicine at UCLA. Currently he is Medical Director of the Jamila Diabetes and Endocrine Medical Center in Thousand Oaks, California.
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