Pre-ergocalciferol

Vitamin D is a pro-hormone that comes in two forms, cholecalciferol (vitamin D3) and ergocalciferol (vitamin Dj) (Haddad and Hahn 1973). Most of vitamin D is obtained as vitamin D3, through synthesis in the skin after exposure to UVB radiation (typically from sunlight) of wavelengths 290-315 nm (Holick 1995). The synthesis converts 7-dehydrocholesterol (DHC-7) to pre-vitamin D3, which is then quickly converted by heat induction to vitamin D3. Overexposure to UVB radiation does not cause vitamin D toxicity as excess pre-vitamin D3 and vitamin D3 is inactivated by radiation (Holick et al. 1981, Webb et al. 1989). Vitamin D3 can also be obtained from animal-based food products, with oily fish (e.g., salmon, sardines, and mackerel) being the best natural source, and egg yolk and meat containing smaller quantities. Vitamin D2 is the plant form of vitamin D and can occur naturally in some types of mushrooms (Lamberg-Allardt 2006). 

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