Edible Mushroom - Vitamin D

Mushrooms that have been exposed to ultraviolet (UV) light contain large amounts of vitamin D₂. Mushrooms, when exposed to UV light, convert ergosterol, a chemical found in large concentrations in many mushrooms, to vitamin D₂. This is similar to the reaction in humans, where Vitamin D₃ is synthesized after exposure to UV light.

Testing conducted by the Pennsylvania State University showed an hour of UV light exposure made a serving of mushrooms contain twice the U.S. Food and Drug Administration's daily recommendation of vitamin D. Testing by the Monterey Mushrooms Company demonstrated 5 minutes of UV light exposure made a serving of mushrooms contain four times the FDA's daily recommendation of vitamin D. High performance liquid chromatography analysis has also demonstrated the effect sunlight has on mushroom vitamin D₂ content.

The ergocalciferol, vitamin D₂, in UV-irradiated mushrooms is not the same form of vitamin D as is produced by UV-irradiation of human skin or animal skin, fur, or feathers (cholecalciferol, vitamin D₃). Although vitamin D₂ clearly has vitamin D activity in humans and formerly was widely used in milk fortification and in nutritional supplements, vitamin D₃ is often used in dairy products. However, any difference in vitamin D bioavailability from the two forms has been adequately disproved to allow reasonable assumption that D2 and D3 are equal for maintaining 25-hydroxyvitamin D status.