Ergocalciferol is a provitamin form of vitamin D, also called vitamin D2. Ergocalciferol is created when ultraviolet light activates ergosterol. 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. 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.
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