Vitamin D

What is vitamin D?

Vitamin D is made up of two fat-soluble compounds. These are vitamin D3, or cholecalciferol, and vitamin D2, or ergocalciferol. Vitamin D is a unique substance, as it is produced in the body when the skin receives solar radiation. The IUPAC systematic name for vitamin D3 is (3S,5Z,7E)-9,10-secocholesta-5,7,10(19)-trien-3-ol and for vitamin D2 is (3S,5Z,7E,22E)-9,10-secoergosta-5,7,10(19),22-tetraen-3-ol

Chemical structure

Vitamin D3 or cholecalciferol is generated in the skin by the action of ultraviolet (UV) rays from sunlight on the compound 7-dehydrocholesterol. Subsequently, cholecalciferol is transformed by hydroxylation in the liver to 25-hydroxycholecalciferol (calcidiol) which is hydroxylated again in the kidney to form 1α-25 dihydroxycholecalciferol (calcitriol) which is the active form.

vitamin D3 cholecalciferol QYSXJUFSXHHAJI-FVUVGDFOSA-N
3D Structure

Like vitamin D3, ergocalciferol (vitamin D2) is a seco-steroid (derived from a steroid that undergoes ring cleavage, in this case the B-ring). Thus, it is formed by photochemical cleavage (by the action of ultraviolet (UV) light) on ergosterol (provitamin D2).

vitamin D2 ergocalciferol MECHNRXZTMCUDQ-CKKMCJOUSA-N
3D Structure


Vitamin D stimulates calcium absorption and helps fight breast and colon cancer. It also helps maintain adequate blood levels of calcium and phosphorus.

Food sources

Cold-water fish, egg yolks, butter and dark green leafy vegetables. In addition, vitamin D, in the form of vitamin D2 (or ergocalciferol) is often added to milk and other foods.

Back to Vitamins page.