Shiitake: benefits, dosage, contraindications

Immunomodulator

Lentinan is a polysaccharide capable of restoring or increasing the responsiveness of host cells to lymphocytokines, hormones and other biologically active substances by stimulating the maturation, differentiation or proliferation of the cells involved in the host defense mechanisms. Thus, lentinan is able to increase the host's resistance against various types of cancer and infectious diseases, including acquired immunodeficiency syndrome (AIDS). Many interesting biological activities of lentinan have been reported, including an increase in the activation of nonspecific inflammatory responses, activation and generation of helper and cytotoxic T lymphocytes, and an increase in immune mediators such as IL-1 and IL-3. Moreover, lentinan can activate the classical and alternative pathways of the complement system and can split C3 into C3a and C3b, thereby enhancing macrophage activation.

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Hypocholesterolemic

The ability of shiitake to reduce blood cholesterol was first reported by Kaneda and Tokuda (1966), who found that a diet supplemented with dried, ground shiitake sporophores reduced mean plasma cholesterol in rats. In hypertensive rats, shiitake lowers VLDL and HDL cholesterol levels. In human studies, serum cholesterol was reduced in groups of women fed fresh, dried, or UV-irradiated shiitake. A similar experiment, conducted on people aged 60 and over, showed that serum cholesterol decreased after 1 week.

Anticancer

Using fractionation and purification methods for polysaccharides, Chihara et al. isolated a water-soluble antitumor polysaccharide named lentinan. It showed significant antitumor activity not only against allogeneic tumors such as Sarcoma 180, but also against various syngeneic and spontaneous tumors. Indeed, injections of lentinan into mice produced either an 80% reduction in tumor size or complete regression in most of the animals tested. This anticancer effect requires an intact immune system and a functional thymus. Administration of immunosuppressive agents such as b-benzylthioguanosine or X-rays together with lentinan reduces the antitumor effect. Lentinan and other polysaccharides from shiitake mushrooms do not directly attack cancer cells, but produce their antitumor effects by activating various immune responses in the host.

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Antiviral

Lentinan is capable of inhibiting the replication of adenovirus type 12, the Abelson virus and the vesicular stomatitis virus (VSV). Lentinan and its sulfated form showed potent anti-HIV activity in vitro, resulting in inhibition of viral replication and cell fusion. On the other hand, a water-soluble mycelial extract known as JLS and JLS-18 is capable of blocking the release of herpes simplex virus type 1 in animals.

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Cardiovascular

The shiitake mushroom is able to reduce serum cholesterol via a factor known as eritadenine, also called "lentinacin" or "lentysine". In mice, eritadenine appears to lower cholesterol levels by accelerating the excretion of ingested cholesterol and its metabolic breakdown, rather than by inhibiting its biosynthesis.

Hypolipidemic

In animal research, the shiitake mushroom reduces plasma levels of cholesterol, triglycerides, and phospholipids. Although the mechanism of action is not clear, potential active constituents include eritadenine, which has shown hypocholesterolemic effects in animal studies.

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Hepatoprotective

A polysaccharide fraction from shiitake mushrooms has shown a hepatoprotective effect in animals as well as the ability to improve liver function and to increase the production of antibodies against hepatitis B. Lentinan improved serum glutamic-pyruvic transaminase (SGPT) and completely restored transaminase (GPT) levels in the livers of mice with toxic hepatitis.

Antifungal

Laboratory research suggests that shiitake mushroom extract inhibits the growth of various types of bacteria and fungi. Indeed, it showed activity against Candida albicans and Saccharomyces cerevisiae.

Antioxidant

In human research, the shiitake mushroom increased levels of reduced glutathione. In a rat model of gestational diabetes, the antioxidant activity of the shiitake mushroom was reported to protect the fetus from damage caused by hyperglycemia.

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Antibacterial

Lentinan is effective against Mycobacterium tuberculosis and Listeria monocytogenes. Oxalic acid is an agent responsible for the antimicrobial effect of Shiitake. It was bacteriostatic against Streptococcus pyogenes, Staphylococcus aureus and Bacillus megaterium.