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Vitamin D metabolism
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Vitamin D is called a vitamin, but it behaves like a hormone: a chemical messenger the body can make on its own. It arrives by two routes, the diet and the skin. In the skin, ultraviolet B radiation converts a molecule called 7-dehydrocholesterol into previtamin D.
What arrives by those two routes is not usable yet. It first passes through the liver, where it is turned into 25-hydroxyvitamin D. That is also the form measured to assess a person's vitamin D status.
The last step happens in the kidney, and that is where it truly becomes active. It arrives raw and passes through two processing stations, the liver and the kidney, before it can work. Once in its active form, it takes on its best-known job in the intestine: it stimulates the absorption of calcium and phosphorus.
In brief
Vitamin D is a hormone obtained from the diet and from the skin, where ultraviolet B radiation converts 7-dehydrocholesterol into previtamin D.
The liver metabolizes it to 25-hydroxyvitamin D, the form used to assess vitamin D status.
The kidney converts it into the biologically active form, which stimulates calcium and phosphorus absorption in the intestine.
It arrives raw and passes through two processing stations, the liver and the kidney, before it can work.
Sources (1)
- National Center for Biotechnology Information, StatPearls PublishingVitamin D, StatPearlsPublished
This page explains the topic in general terms; it does not tell anyone what treatment to follow.
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