The production of D-3 in the human body is a photochemical reaction that occurs when the skin is exposed to ultraviolet radiation (UVB). Additionally, it is found in a few foods, mainly animal-based, such as salmon, tuna, sardines, mushrooms, and egg yolk.

It is also known to contribute to the normal absorption/utilization of calcium and phosphorus, normal blood calcium levels, maintenance of normal bones, maintenance of normal muscle function, maintenance of normal teeth, normal function of the immune system, and has a role in the process of cell division.