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Medicinal mushrooms are mushrooms used in the practice of medicine. Many species of mushrooms have been used in folk medicine for thousands of years. The use of mushrooms in folk medicine is best documented in the East. Medicinal mushrooms are now the subject of study for many ethnobotanists and medical researchers. The ability of some mushrooms to inhibit tumor growth and enhance aspects of the immune system has been a subject of research for approximately 50 years. Preclinical studies suggest that compounds from up to 200 species of mushrooms may inhibit tumor growth, but required dosage and effects on humans is mostly unknown.
Fungus research has led to the discovery of many pharmaceutical drugs, including penicillin, ciclosporin, griseofulvin, cephalosporin, ergometrine as well as the popular statin class of cholesterol drugs. Statins, like lovastatin and mevastatin were first isolated from different strains of fungi. Recent research has found lovastatin is present in the popular oyster mushroom, mushrooms produce vitamin D when exposed to UV light, and fungi are a potential source of taxol. Currently, researchers are focusing on mushrooms that appear to offer anti-cancer and immune system enhancing activity.
Some mushrooms have long been used as a folk medicine in China, Japan, Russia, and the Middle East. Certain mushrooms were thought to be able to benefit a wide variety of ailments. In other parts of the world like the UK, Ireland, and North America there is no record of the use of mushrooms for folk medicine, instead mushrooms were known as being potentially poisonous and were associated with uncleanliness.
In 2008, researchers at the University of California, Davis published a review of medicinal mushroom research and encouraged further research by way of clinical trials. However, the review stated that currently there is not enough known about medicinal mushrooms to begin promoting their use in the treatment of specific diseases. Medicinal mushroom research in the United States is currently active, with studies taking place at City of Hope National Medical Center, as well as the Memorial Sloan–Kettering Cancer Center.
Medicinal mushroom research
Research suggests the compounds in medicinal mushrooms most responsible for up-regulating the immune system, are a diverse collection of polysaccharides, particularly beta-glucans, and to a lesser extent, alpha-glucans. These polysaccharides are made up of repeating units of D-glucose monomers and come in a large variety of shapes and molecular weights. Proteins can also be attached to these mushroom polysaccharides. An example of this would be the protein-bound beta-glucans that are contained in Polysaccharide-K.
Beta-glucans are currently known as "biological response modifiers", and their ability to activate the immune system is well documented. Specifically, beta-glucans stimulate the innate branch of the immune system. Research has shown beta-glucans have the ability to stimulate macrophage, NK cells, T cells, and the production of immune system cytokines. Research has also suggested that polysaccharides present in medicinal mushrooms may enhance dendritic cell function. The mechanisms in which beta-glucans stimulate the immune system is only partially understood. One mechanism in which beta-glucans are able to activate the immune system, is by interacting with the Macrophage-1 antigen (CD18) receptor on immune cells. Other human receptors have been identified as being able to receive signals from beta-glucans such as Toll-like receptor 2, Dectin-1, lactosylceramide, and scavenger receptors.
Mushrooms like other vegetables, are known to contain antioxidants. Examples of mushrooms with documented antioxidant activty include Maitake, Agrocybe aegerita, Reishi, Agaricus blazei, Oyster mushrooms, Agaricus bisporus, Chaga, and Shiitake. Chemical analysis has shown that a specific antioxidant found in some mushrooms like Flammulina velutipes and Agaricus bisporus is ergothioneine.
Effect on blood sugar
Research has shown that some medicinal mushrooms may be able to lower elevated blood sugar levels. Mushrooms noted for this ability include Reishi, Agaricus blazei, Chaga, Agrocybe aegerita, and Cordyceps. Explanation for this effect is limited, with the exception of the Maitake mushroom. The Maitake mushroom's ability to lower blood sugar levels has been explained by the fact that the mushroom naturally contains a compound known as an alpha-glucosidase inhibitor.
Effect on cholesterol
Some mushrooms like Agaricus blazei and Reishi have been shown to be able to have an inhibitory effect on cholesterol levels. Shiitake mushrooms have been found to contain a specific anti-cholesterol compound known as eritadenine. Oyster mushrooms have been found to naturally contain a statin drug known as lovastatin (brand name: Mevacor, Altoprev) a drug used to lower cholesterol. Tests have shown the oyster mushroom contains up to 2.8% Lovastatin on a dry weight basis. Animal research has shown that Oyster mushroom consumption lowers cholesterol levels.
Direct anti-hormone activity
Mushrooms may be able to influence the production of certain human hormones, due to evidence from enzyme assay analysis. Mushrooms like Agaricus bisporus may be able to partially inhibit the activity of aromatase, the enzyme responsible for producing estrogen. Mushrooms like Reishi may be able to partially inhibit the activity of 5-alpha reductase, the enzyme responsible for producing dihydrotestosterone.