The Physiology of Vitamin D

A vitamin is an organic compound the body cannot make but is necessary for its proper functioning. Vitamins are vital for the proper growth of the body. It also helps in the functioning and the overall development of the body apart from supporting the metabolic activities in the body.

Vitamin D, being known as a Vitamin naturally makes us inclined to think that like any other vitamin we can get it from our daily diet if it is a balanced one. However, unlike, other Vitamins, Vitamin D isn’t actually a vitamin. Dietary sources of Vitamin D are limited, but you can certainly make it in your skin or you can get it through Vitamin D supplements.


The far reaching effects of Vitamin D are aligned with how hormones act on our metabolic pathways, cellular functions and in the expression of numerous genes in the body. The active metabolic product of Vitamin D in the body is 1, 25-dihydroxyvitamin D or calcitriol.

Calcitriol is a secosteroid hormone that directly or indirectly targets about 6 percent of the human genome or more than two thousand genes.

The body synthesizes hormones from simple precursors. They later go to distant tissues to have their intended effect and make multiple metabolic improvements. Vitamin D requires an outside source to trigger a sequence of events. Here, the precursor of a cholesterol-like molecule found in the skin cell called 7-dehydrocholesterol and better known as pro-vitamin D3 starts the process by absorbing just the ultraviolet B portion of sunlight to create what’s called Pre-vitamin D3. The body’s heat prompts Pre-vitamin D3 to quickly rearrange itself and transform into vitamin D that immediately exits the skin cell for the bloodstream.

You cannot wash off Vitamin D if you bathe because it is made inside the skin not on it.

Hormones are more complex molecules when compared to vitamins. They act in two ways:

  • They enter the cell and travel through the cytoplasm until they reach the nucleus where they influence its activity;
  • They can bind to a receptor on a cell membrane and thereby transmit a signal to the cell telling it to chance what it is doing in any number of ways.

Before vitamin D can act as a hormone, it must go through two steps of activation – one in the liver and the other in the kidneys. Activated vitamin D mainly works by interacting with its receptor within the cell’s nucleus.

An SPF 8 sunscreen absorbs about 90 percent of UVB radiation and reduces your ability to make vitamin D in your skin by about 90 percent. SPF 30 cuts down your Vitamin D making ability by 99 percent.

So, skip that sunscreen for your 15 minutes dose of Vitamin D every day. Have a happy Sun-day!

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