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.
The UV treatment did not reportedly reduce the other vitamins present in mushrooms including B1, B2, B3, B5 and folate. The essential minerals selenium, potassium, copper, iron and phosphorus are also present in mushrooms. For vegans, especially mushrooms represent an excellent way of boosting vitamin D levels without compromising their ethics.
Almost a third of Australian adults are deficient in vitamin D which can cause joint pain and increased risk of osteoporosis, as vitamin D is crucial in bone formation. Given it can be hard to get enough vitamin D in winter, it may well be worth hunting down mushrooms in the supermarket marked as having been exposed to light to boost their vitamin D content.
If you are taking a vitamin D supplement it will likely be listed cholecalciferol (D3) rather than the ergocalciferol (D2) found in mushrooms. D3 is primarily generated by the body after exposure to sunlight [See recommendations for sunlight exposure here] and is longer lasting in the body. So make sure you supplement your mushrooms with a walk in the sunshine when you can!