There are two major forms of Vitamin D - vitamin D2 (ergocalciferol - plant derived) and vitamin D3 (cholecalciferol - animal derived). Both forms have been shown to be equally efficacious. Since our bodies can produce vitamin D by the action of sunlight on the skin, it is often referred to as the 'sunshine vitamin'. Vitamin D is important to many body functions, particularly in bone health, mood and immunity. A well-known deficiency symptom is rickets.