Vitamin D

Vitamin D comes from two sources: endogenous, which is produced in the skin on exposure to sunlight, and exogenous, which is ingested in foods and supplements. The chemical structures of these types of vitamin D are slightly different, and they are named vitamin D₂ (ergocalciferol) and vitamin D₃ (cholecalciferol). The D₂ form is found in foods and in most vitamin preparations and supplements. Vitamin D₃ is the form produced in the body and is also used in some supplements. Vitamin D₂ and D₃ are equally effective.

Many tests for 25-hydroxyvitamin D do not distinguish D₂ and D₃ forms of the vitamin and report only a total 25-hydroxyvitamin D. Newer methods, however, may report levels of both 25-hydroxy D₂ and D₃ and then add them together for a total 25-hydroxyvitamin D level. Total 25-hydroxyitamin D concentration is what is used to assess vitamin D status.

Sources and Forms of Vitamin D

The main role of Vitamin D is to help regulate the absorption of calcium, phosphorus, and (to a lesser extent) magnesium. Vitamin D is vital for the growth and health of bone; without it, bones will be soft, malformed, and unable to repair themselves normally, resulting in diseases called rickets in children and osteomalacia in adults. Vitamin D has also been implicated in the regulation of autoimmunity, metabolic function, and cancer prevention.