Normally grown in the dark, mushrooms are pretty low in vitamin D unless exposed to UVB light. Researchers have discovered that exposing Oyster, Shiitake or even common button mushrooms to ultraviolet light, boosts the vitamin D levels to impressive numbers. (as much as 46,000iu).
They found that exposing the gills (the ridges underneath the cap) generates the maximum conversion to vitamin D. The type of vitamin D mushrooms have is vitamin D(2), a slightly different version of vitamin D and is not as bio-available as D(3)
Our enzymes convert both D vitamins into 25-hydroxyvitamin D, and then into the active form of 1,25-dihydroxyvitamin D in our kidneys
However, boosting the levels of vitamin D(2) is said to be a beneficial addition to D(3) from sunlight and foods such as dairy and plant milks fortified with vitamin D, sardines, beef liver, cod liver oil, salmon and tuna fish. Mushrooms are also said to have a really good variety of B vitamins plus selenium, zinc, copper, vitamin C and potassium. Best of all, they’re low carb.
Mushrooms can be best exposed during summer months face up with the stems removed and the gills pointing upward (button mushrooms, slice them lengthwise to expose the gills). Place in the sunlight between 10am and 6pm to give eight hours of exposure. This process can be repeated until fully dehydrated and can be stored for the winter months.