Shiitake: Benefits, Dosage, Contraindications

Immunomodulator

Lentinan is a polysaccharide capable of restoring or enhancing host cell reactivity to lymphocytokines, hormones, and other biologically active substances by stimulating the maturation, differentiation, or proliferation of cells involved in host defense mechanisms. Thus, lentinan can enhance the host's resistance against various types of cancer and infectious diseases, including acquired immune deficiency 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 improvement of immune mediators such as IL-1 and IL-3. On the other hand, lentinan can activate normal and alternate complement pathways and can split C3 into C3a and C3b thereby enhancing the activation of macrophages.

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Hypocholesterolemic

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

Anticancer

By using methods for fractionating and purifying 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 autologous tumors. Indeed, lentinan injections in mice resulted in either an 80% reduction in tumor size or complete regression in most test animals. This anticancer effect requires an intact immune system and a functional thymus. Administering immunosuppressive agents such as b-benzylthioguanosine or X-rays with lentinan diminishes the antitumor effect. Lentinan and other polysaccharides in shiitake mushrooms do not directly attack cancer cells but exert their antitumor effects by activating different host immune responses.

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Antiviral

Lentinan is capable of inhibiting the replication of adenovirus type 12, Abelson virus, and Encephalitis virus (VSV). Lentinan and its sulfated form displayed strong anti-HIV activity in vitro leading to inhibition of viral replication and cell fusion. Additionally, a water-soluble mycelium extract known as JLS and JLS-18 has the ability to block the release of herpes simplex virus type 1 in animals.

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Cardiovascular

Shiitake can lower blood serum cholesterol via a factor known as eritadenine, also referred to as "lentinacine" or "lentysine." In mice, eritadenine appears to reduce cholesterol levels by accelerating the excretion of ingested cholesterol and its metabolic breakdown rather than inhibiting its biosynthesis.

Hypolipidemic

In animal research, shiitake mushrooms reduce plasma levels of cholesterol, triglycerides, and phospholipids. Although the mechanism of action is unclear, potential active constituents include eritadenine, which has shown hypocholesterolemic effects in animal research.

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Hepatoprotective

A polysaccharide fraction from shiitake mushrooms has shown liver protective effects in animals as well as the ability to improve liver function and increase antibody production against hepatitis B. Lentinan improved serum glutamic pyruvic transaminase (SGPT) and fully restored levels of transaminases (GPT) in mice with toxic hepatitis.

Antifungal

Laboratory studies suggest that shiitake mushroom extract inhibits the growth of various types of bacteria and fungi. It has shown activity against Candida albicans and Saccharomyces cerevisiae.

Antioxidant

In human research, shiitake mushroom increased levels of reduced glutathione. In a rat gestational diabetes model, it was reported that the antioxidant activity of shiitake mushrooms protects 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.