vitamin D

Vitamin D is a group of fat-soluble secosteroids responsible for intestinal absorption of calcium and phosphate.

In humans, vitamin D is unique because it can be ingested as cholecalciferol (vitamin D3) or ergocalciferol (vitamin D2) and because the body can also synthesize it when sun exposure is adequate.

Although vitamin D is commonly called a vitamin, it is not actually an essential dietary vitamin in the strict sense, as it can be synthesized in adequate amounts by most mammals exposed to sunlight.