Ergocalciferol may be used as a vitamin D supplement, whereas cholecalciferol (vitamin D3) is produced naturally by the skin when exposed to ultraviolet light. Ergocalciferol (D2) and cholecalciferol (D3) are considered to be equivalent for vitamin D production, as both forms appear to have similar efficacy in ameliorating rickets and reducing the incidence of falls in elderly patients. Conflicting reports exist, however, concerning the relative effectiveness, with some studies suggesting that ergocalciferol has less efficacy based on limitations in absorption, binding, and inactivation. A meta-analysis concluded that evidence usually favors cholecalciferol in raising levels in blood, although it stated more research is needed.
Ergocalciferol and metabolites have lower affinity to the vitamin D-binding protein compared to the D3 counterparts. The binding affinity of ercalcitriol to the vitamin D receptor is similar to that of calcitriol. Ergocalciferol itself and metabolites can be deactivated by 24-hydroxylation.
Cladina arbuscula specimens grown under different natural conditions: The contents of vitamin D3 range from 0.67 to 2.04 μg/g (27 to 82 IU/g) dry matter in the thalli of C. arbuscula specimens grown under different natural conditions, while provitamin D3 could not be detected. The ranges for provitamin D2 and vitamin D2 were 89-146 and 0.22-0.55 μg/g (8.8 to 22 IU/g) dry matter, respectively, while the contents of provitamin D3 were below the detection limit (0.01 μg/g dry matter). Vitamin D levels correlate positively with UV irridation.
Fungus, from USDA nutrient database (per 100g), D2 + D3:
The vitamin D2 content in mushrooms and C. arbuscula increase with exposure to ultraviolet light.Ergosterol (provitamin D2) found in these fungi is converted to previtamin D2 on UV exposure, which then turns into vitamin D2. If there is little exposure to UV light (or sunlight), little vitamin D will form.
When fresh mushrooms or dried powders are purposely exposed to artificial sunlight by use of an industrial ultraviolet lamp, vitamin D2 levels can be concentrated to much higher levels. The irradiation procedure does not cause significant discoloration, or whitening, of mushrooms. Claims have been made that a normal serving (approx. 2 oz or 60 grams) of fresh mushrooms treated with ultraviolet light have increased vitamin D content to levels up to 80 micrograms or 3200 IU if exposed to just 5 minutes of UV light after being harvested.
Button mushrooms with enhanced vitamin D2 content produced this way functions similarly to a vitamin D2 supplement; both effectively improves vitamin D status. Vitamin D2 from UV-irradiated yeast baked into bread or mushrooms is bioavailable and increases blood levels of 25(OH)D.
Viosterol, the name given to early preparations of irradiated ergosterol, is essentially synonymous with ergocalciferol.
Ergocalciferol is manufactured and marketed under various names, including Deltalin (Eli Lilly and Company), Drisdol (Sanofi-Synthelabo) and Calcidol (Patrin Pharma).
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^See "Viosterol" and "Calciferol" at Merriam-Webster Medical Dictionary, e.g., "Archived copy". Archived from the original on 2014-07-14. Retrieved 2014-07-10.CS1 maint: Archived copy as title (link) and "Archived copy". Archived from the original on 2014-07-14. Retrieved 2014-07-10.CS1 maint: Archived copy as title (link) , accessed 10 July 2014.