Raw, uncooked mushrooms usually provide a little over 2mcg of vitamin D per 100g. The Australian recommended daily intake (RDI) for vitamin D is 5mcg so you would have to eat three cups of raw mushrooms to meet your daily vitamin D needs. Even the most avid mushroom fans might baulk at that! Mushrooms are grown in the dark, and vitamin D is usually associated with sunlight so you might wonder why there is any vitamin D in mushrooms at all. Interestingly combining the light and the dark is where things get exciting!
Scientists have shown that exposing mushrooms to just a few seconds of sunlight (or any ultraviolet (UV) light), before packaging, converts the ergosterol naturally found in mushrooms to ergocalciferol (also known as D2) and massively increases the amount of vitamin D in each mushroom.
Analysis done by Food Standards Australia confirmed that this UV light treatments of freshly picked mushrooms, before packaging, boosted the vitamin D content up from 2mcg to a whopping 26mcg when uncooked. Cooked mushrooms jumped even further, up to a 52mcg per 100g.