Question

How active Vitamin D is produced by the epidermis

Answer 1

Vit D is produced in its active form by both keratinocytes of the epidermis and the kidneys in our body.

The precursor of Vit D in our body is 7-dehydrocholestrol (7-DHC). On recieving UV-B radiations, this 7-DHC is converted to Pre-D3 which is rapidly converted to D3 if temperature is maintained around 37 degrees.

Pre D3 production does not reach toxicity level because the excess amount is photoconverted into lumisterol and tachysterol.

The PTH hormone stimulates the production of active Vit D in the keratinocytes in a cAMP independent pathway.

The keratinocytes contain the enzymes vitamin D-25 hydroxylase (CYP27A) and 25OHD-1α-hydroxylase (CYP27B1) which convert D3 to the active circulating form of 1,25(OH)2 D3.