Also Known As: Vitamin D2, Ergocalciferol, Drisdol, Calcidol
Ergocalciferol is a provitamin form of vitamin D, also called vitamin D2. In isolated manufactured formats, it is marketed under various names including Deltalin (Eli Lilly and Company), Drisdol (Sanofi-Synthelabo), and Calcidol (Patrin Pharma). Ergocalciferol is created when ultraviolet light activates ergosterol.
Conflicting evidence exists for how similarly D2 and D3 behave in the body and whether they are equally active or efficient in production of 25-hydroxyvitamin D (25(OH)D), the active hormone. Some preliminary studies indicate D3 is more potent, while others report equal efficacy. Both forms appear to have similar efficacy in ameliorating rickets and reducing the incidence of falls in elderly patients.
The metabolism of each appears to be different, with the vitamin D binding protein possibly having greater affinity for 25(OH)D3 than for 25(OH)D2, as shown in one study. Cholecalciferol (vitamin D3) is sensitive to UV radiation and rapidly, but reversibly, forms other sterols which can further irreversibly convert to ergosterol.