To get all vitamins D is to go outside. That’s because vitamin D is made when the sun shines on the human skin.
In the skin, 7-dehydrocholesterol in the epidermis and dermis changes conformation ultraviolet B (UVB) radiation in the wavelength range of 280-315 nm passes through these skin layers to form pre-vitamin D3.
Subsequent enzymic conversion occurs outside the skin predominantly, although both the necessary enzymes, 25-hydroxylase and 1 α-hydroxylase are present in the skin. Thus the active form of vitamin D,1,25-dihydroxyvitamin D3 may be present in the skin.
While the reaction to form pre-vitamin D3 takes minutes, the reaction converting it to vitamin D3 takes hours to occur and is a rate-limiting step.
The vitamin D3 gets carried to liver, where it gets changes into a more active form; from there, it goes to kidneys, where it becomes even more active.
Some of the vitamin D3 stays in liver and kidneys, where it helps reabsorb calcium from blood.
Synthesis of vitamin D in the skin
