Vitamin D has two forms: vitamin D2 (ergocalciferol) derived from plant-based sources and vitamin D3 (cholecalciferol) found in some fish and meat and produced by your body when exposed to sunlight.

There are two types of vitamin D supplements available for over-the-counter purchase (vitamin D2 and vitamin D3). Vitamin D3 is the type that most experts believe should be utilized in clinical ...