Whatever your favourite — crimini, enoki, oyster, portobello, shiitake or white button — all mushrooms are loaded with essential nutrients. Mushroom nutrition Many varieties of mushrooms contain good-for-your-bladder selenium and, like us, they produce vitamin D when exposed to sunlight. Oyster mushrooms are a good source or iron. Plus, they’re low in calories: Six medium white, for example, have just 22. Here are some of the many health benefits of mushrooms. Increase your vitamin D Yes, vitamin D! Mushrooms are the only fruit or vegetable source of this critical vitamin. Like humans, mushrooms produce vitamin D when in sunlight. Exposing them to high levels of ultraviolet B just before going to market converts more of the plant sterol ergosterol into the so-called sunshine vitamin. In the U.S., portobellos fortified with vitamin D are already being sold, with a three-ounce (85-gram) serving providing about 400 IU of v