Ergocalciferol may be used as a vitamin D supplement, and a 2011 clinical guideline considered it to be as effective as cholecalciferol (vitamin D3) which is produced naturally by the skin when exposed to ultraviolet light. It is manufactured and marketed under various names, including Deltalin (Eli Lilly and Company), Drisdol (Sanofi-Synthelabo) and Calcidol (Patrin Pharma).
Cladina arbuscula specimens grown under different natural conditions: The contents of vitamin D3 range from 0.67 to 2.04 μg/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 dry matter, respectively, while the contents of provitamin D3 were below the detection limit (0.01 μg/g dry matter).
Ergocalciferol is produced in fungi synthetically through irradiation of ergosterol. Human bioavailability of vitamin D2 from vitamin D2-enhanced button mushrooms via UV-B irradiation is effective in improving vitamin D status and not different from a vitamin D2 supplement. Vitamin D2 from UV-irradiated yeast baked into bread is bioavailable. By visual assessment or using a chromometer, no significant discoloration of irradiated mushrooms, as measured by the degree of "whiteness", was observed. Claims that a normal serving of mushrooms treated with ultraviolet light provides the equivalent of 3,500 International Units of vitamin D when exposed to ultraviolet light after harvest have gained popular attention.
Research concerning efficacy of vitamin D2 and D3
Conflicting evidence exists for how similarly D2 and D3 behave in the body and whether they are equally active or efficient in production of 1,25-hydroxyvitamin D (1,25(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.
One study found low vitamin D2 levels in patients with Alzheimer's disease, but this observational study did not prove cause or effect related to ergocalciferol and vitamin D2 deficiency in the diet.
^Science Service (1930) Viosterol official name for irradiated ergosterol, J. Chem. Educ. 7(1) 166, DOI: 10.1021/ed007p166, see [pubs.acs.org/doi/abs/10.1021/ed007p166, accessed 10 July 2014.
^See "Viosterol" and "Calciferol" at Merriam-Webster Medical Dictionary, e.g.,  and , accessed 10 July 2014.
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^Fosnight, S. M.; Zafirau, W. J.; Hazelett, S. E. (2008). "Vitamin D Supplementation to Prevent Falls in the Elderly: Evidence and Practical Considerations". Pharmacotherapy28 (2): 225–234. doi:10.1592/phco.28.2.225. PMID18225968. edit
^Iltaf Shah; Petroczi, Andrea; Tabet, Naji; Klugman, Anthony; Isaac, Mokhtar; p. Naughton, Declan (2012). "Low 25OH Vitamin D2 Levels Found in Untreated Alzheimer's Patients, Compared to Acetylcholinesterase-Inhibitor Treated and Controls". Current Alzheimer Research9 (9): 1069–1076. doi:10.2174/156720512803568975. ISSN1567-2050. PMID22876849.