Although considered a vegetable, mushrooms are neither a plant nor animal food. They are a type of fungus that contains a substance called ergosterol, similar in structure to cholesterol in animals. Ergosterol can be transformed into vitamin D with exposure to ultraviolet light. Mushrooms vary in appearance with more than 10,000 known types, but generally they are distinguished by a stem, fleshy rounded cap, and gills underneath the cap. China and the U.S. are among the top five producers of mushrooms worldwide.
Are mushrooms a good source of vitamin D?
Dried mushrooms also contain the vitamin. Some estimates show dried mushrooms to contain about 600 IU of vitamin D2 per 3.5 ounces if stored in dark, cool, dry conditions for up to 6 months (the vitamin may start to break down after that time). 
Humidity and cooking mushrooms in water do not appear to affect vitamin D content in mushrooms, but cooking them in fat (such as oils) can cause the vitamin to leach out because it is fat-soluble.
Mushrooms and Health
Edible mushrooms like maitake and shiitake have also been used as medicine throughout history. Other mushrooms that are too tough to eat have been used solely for medicinal purposes such as reishi. Plant chemicals and components in mushrooms may exert antioxidant, anti-inflammatory, and anticancer effects, but the exact mechanism is still unclear and an area of active research.  Animal and cell studies show that mushrooms can stimulate the activity of immune cells, macrophages, and free radicals that can stop the growth and spread of tumor cells and cause existing tumor cells to die.  Various polysaccharides in mushrooms including beta-glucans are believed to exert these cancer-fighting properties. [4,6]
Cardiometabolic diseases and cancer
There are thousands of varieties of mushrooms, with different colors, shapes, and sizes. Because some wild mushrooms can cause stomach upset or allergic reactions, or may even be poisonous, your safest bet is to stick to supermarket varieties and avoid picking and eating raw wild mushrooms on your own.
The common button mushroom (Agaricus bisporus) is the most common in the U.S. It is the mildest-tasting mushroom and can be eaten raw or cooked.
Other types of mushrooms available for sale include:
Chanterelle: the cap is a wavy golden trumpet-like shape
Enoki: long, thin white stems with small white caps that are eaten raw or cooked
Maitake: a head that resembles flowering leaves
Morel: the cap is a spongy dimpled oblong shape
Oyster: a fan-shaped delicate cap
Porcini: a reddish-brown rounded cap with a thick cylindrical stem
Shiitake: a dark brown umbrella cap with a thin cream-colored stem
Mushrooms that have been specially treated with UV light may carry a label on the front of the package that says “UV-treated” or “rich in vitamin D,” or display the exact amount of vitamin D they contain.
Is a truffle a mushroom?
Select mushrooms with firm whole caps with an even texture. They should be refrigerated until use, but ideally within one week. Do not wash or clean them until just before using. Storing in a brown paper bag with the top open will help to absorb moisture and keep them from spoiling, as opposed to tight plastic wrapping that traps moisture. Because they are about 80-90% water, mushrooms do not freeze well, becoming mushy when defrosted.
Mushrooms are delicate and should be cleaned gently. Either place them under gentle running water to release any dirt or brush dirt off with a dampened paper towel.
Cooking mushrooms in high-temperature water such as boiling and microwaving may cause its water-soluble nutrients (B vitamins, potassium) to escape in the cooking water. Sautéing quickly over high heat, or simmering over low heat, such as in soups, are ideal cooking methods for preserving nutrients.
- Add chopped mushrooms into salads, omelets, scrambled eggs, stir-fries, pasta sauces, chilis, or soups.
- Sauté mushrooms in olive oil and add to cooked pasta or whole grains.
- Grill large portobello mushroom caps. Remove the stems and gills if desired. Marinate the mushrooms for 10 minutes in a favorite sauce. Grill for about 3 minutes each side until they caramelize.
- Mushrooms make a great replacement for meat because of their umami flavor. Replace about a quarter to a half of the meat in a recipe with chopped mushrooms.
What is umami?
- Wild Mushroom Soup with Soba
- Barley Roasted Portobello and Fennel Salad
- Braised Oyster Mushrooms, Coconut, and Macadamia
- Marinated Shiitake Mushroom and Cucumber Salad
- Pan Roasted Wild Mushrooms with Coffee and Hazelnuts
- Mushroom Barley Risotto
- Mushroom Stroganoff
- Mushroom Tofu Veggie Burger
- Three-Green & Wheat Berry Salad with Mushroom “Bacon”
- White Beans, Wild Rice and Mushrooms
Did You Know?
Not all mushrooms are edible. Wild mushrooms with white gills or a ring around the stem are considered poisonous. Some other inedible mushrooms look like edible mushrooms, so unless one is trained in recognizing wild mushrooms, it’s best to find your mushrooms at the market!