In the United States, vitamin D supplementation is primarily available as vitamin D2 (ergocalciferol) and vitamin D3 (cholecalciferol). Although these two have historically been considered interchangeable and equipotent, the current body of literature strongly supports the preference of Vitamin D3 (cholecalciferol) over D2 (ergocalciferol).
Vitamin D2 versus Vitamin D3
Vitamin D3 (cholecalciferol) is produced by the human body in response to sunlight and is also available through dietary sources, such as fish. In contrast, vitamin D2 (ergocalciferol) is not produced in the human body, but is created by exposing certain plant-derived materials to ultraviolet light.