ABSTRACT
Vitamin D (calciferol), first discovered by McCollum in 1922, is essential for the proper formation of the skeleton and for mineral homeostasis.1,2 Following the discovery of vitamin D, two nutritional forms of vitamin D were isolated: vitamin D2 (D2 or ergocalciferol) and vitamin D3 (D3 or cholecalciferol). The chemical structures of D2 and D3 were identified independently by two groups, a British group led by Askew3 and a German group led by Windaus.4,5 Windaus’s group provided the chemical synthesis of the vitamin D compounds and confirmed their structures. In 1928, Windaus received the Nobel Prize in Chemistry for his contributions. The structures of the nutritional forms of vitamin D are provided in Figure 5.1. Vitamin D3 is synthesized from 7-dehydrocholesterol in the skin upon exposure to ultraviolet (UV) rays from the sun6-8 while vitamin D2 is produced through irradiation of plant sterols.3
