Preliminary Research suggests that exposure of mushrooms to ultraviolet light can be the source of the vitamin D. Mushrooms can emerge as a major source of vitamin D in this way.
Exposing to UV light would be easy and low cost to do. It can turn a agricultural product to a plant with source of vitamin D.
A white mushrooms contains 869 percent of daily value of the sunshine vitamin. It should be exposed to UV light for just five minutes after being harvested. Farmers raise the mushrooms in the dark. They switch on lights only at the time of harvesting. That contains negligible amounts of vitamin D usually.
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