Doing one simple thing to your shop-bought mushrooms can transform them from containing virtually zero Vitamin D to one of nature's richest food sources in as little as an hour or two, according to Penn State University. Popped on a sunny windowsill, the mushrooms (which are commercially grown in near total darkness) will react to the UV light, churning out loads more antioxidant Vitamin D to defend themselves from damage from solar radiation.
The Penn State team found that a serving of white button mushrooms exposed to UV lamps for just 1 second could go from containing essentially no Vitamin D, to an astonishing 824% of your daily value.
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When they tried the same thing with shiitake and oyster mushrooms, their vitamin D content skyrocketed way over 1000 times what you need to consume each day. In the world of food science this really is as close as you can get to alchemy, all for very little effort.
With such tiny amounts of UV light needed to create such an enormous impact, it doesnt have to be a blazingly hot day either. Simply lay your mushrooms out on a windowsill for an hour or two anytime between 10am and 3pm and their levels should rise significantly. As the gill tissue (the brown underside of the caps) is more sensitive to light, placing these with their gills facing up will trigger the strongest spike.