Shiitake is a medicinal mushroom. It is also used as a popular culinary ingredient in most of the world. Shiitake mushrooms grow upon the trunks and stumps of trees. They are a dark brown mushroom with a firm texture and woody flavor.
Shiitake have been used in traditional Chinese, Japanese, and Korean medicine for thousands of years.  In Traditional Chinese Medicine (TCM) Shiitake is believed to stimulate the “Qi,” or life force. It is believed to promote longevity, stimulate the immune system, treat gastrointestinal complaints, protect the heart, and prevent cancer. Today, many of the indications in TCM for Shiitake have been proven in research and western medicine as true properties of the mushroom.
Shiitake mushrooms are a great addition to the culinary shelf. They are rich in B vitamins (B1, B2, B3, B6) and specific amino acids. They are also high in minerals; especially selenium, zinc, and copper. Shiitake mushrooms are considered a source of fiber as well. 
The high vitamin and mineral content may be a reason that Shiitake is so helpful for many health complaints. However, the most active constituents found in Shiitake are the polysaccharides, Lentinan and cortinelin.  Lentinan has received the most attention, being responsible for the stimulation of the immune system. In particular, Lentinan stimulates T-Lymphocytes, the first of the immune cells to take action against an invading bacteria or virus. Lentinan is a polysaccharide from the group known as Beta 1,3-glucans. (See article) Cortinelin, the other main polysaccharide in Shiitake, is responsible for antibacterial action; although it has not been studied as extensively as Lentinan.
Shiitake mushrooms are ascribed as being immune stimulating, anti-cancer, and nutritional.
In research, the part of the mushroom most commonly used is the cap. However, the whole mushroom can be used medicinally. Some sources recommend using the immature body, before the cap is produced.
For food preparation purposes, the mushrooms can be used dried or fresh. The cap is the easiest to use in dishes, as the stem is often tough and ‘woody.’
Shiitake Mushroom Uses
Shiitake mushroom can be used as an adjunctive treatment for HIV.  As mentioned, It has certain immuno-stimulating properties, in particular T cells. Lentinan was also found to stimulate the production of CD4 cells, the main cell affected by HIV. Lentinan achieved this effect when combined with other anti-HIV medications.
- Shiitake mushroom is prized for it’s anti-tumor effects.  The main constituent, Lentinan, has been shown to inhibit several cancers in vitro, and is widely used in Japan as a treatment for cancer along side chemotherapy drugs.
- Lentinan has been shown to inhibit colon cancer in vitro. It stopped progression of cancers once it was established. 
- Lentinan has been used in patients with gastric (stomach) cancer. In some research studies, it was shown to improve quality of life and prolong survival when combined with conventional treatment of chemotherapeutic drugs. 
- There are also suggestions that Shiitake may be helpful for individuals with Hepatitis B. It been employed in several formulas in the East to treat Hepatitis B with varying success.
- Shiitake may also be effective for lowering blood pressure and decreasing cholesterol, affording some protection against the development of cardiovascular disease. More research is needed in these areas.
The recommended dosage for Shiitake varies. A pure extract of Lentinan can be given in doses of 1 - 3 grams, three times a day. Dried mushroom can be given in larger doses of 6 - 16 grams per day. A tincture of Shiitake can be taken in a dose of 2 - 4 milliliters per day.
The addition of Shiitake mushrooms to any dish can only have a positive effect on ones health.
Side effects of ingestion of Shiitake mushroom include diarrhea and bloating. These side effects occurred after ingestion of a large amount of Shiitake, far exceeding the recommended dosage. 
Shiitake mushrooms is considered safe for all populations, including pregnant and nursing women. Individuals who may have a hypersensitivity, or allergy, to mushrooms should avoid them.
There are no toxicity or overdose potential with Shiitake mushroom, aside from the GI complaints.
1. http://www.pdrhealth.com/drug_info/nmdrugprofiles/herbaldrugs/101840.shtml Shiitake Mushroom. March 2005.
2. http://www.pdrhealth.com/drug_info/nmdrugprofiles/herbaldrugs/101840.shtml Shiitake Mushroom. March 2005.
3. Gordon M et al. A placebo controlled trial of the immune modulator, Lentinan, in human immune deficiency positive patients. A Phase I/II trial. J Med. 1998; 29(5-6): 305-330.
4. Sia GM, Candlish JK. Effects of Shiitake (Lentinan edodes) extract on human neutrophils and the U937 monocytic cell line. Phytother Res. 1999 Mar; 13(2): 133-137.
5. Ng ML, Yap AT. Inhibition of human colon carcinoma development by Lentinan from Shiitake mushroom (Lentinan edodes). J Altern Complement Med. 2002 Oct; 8(5): 581-589.
6. Nakano H et al. A multi-institutional prospective study of Lentinan in advanced gastric cancer patients with unresectable and recurrent disease: effect on prolongation of survival and improvement of quality of life. Kanagavia Lentinan Research Group. Hepatogastroenterology. 1999 Jul-Aug; 46(28): 2662-2668.
7. Levy AM et al. Eosinophils in GI symptoms after ingestion of Shiitake mushroom. J Allergy Clin Immunol. 1998 May; 101(5): 613-620.