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Moderate evidenceImmunity

Shiitake Extract

Whole shiitake mushrooms and their beta-glucan lentinan have measurable immune effects in humans — including a survival benefit as injected lentinan alongside gastric cancer chemotherapy — but that drug is not the capsule on the shelf. Oral supplement evidence is thin and rests largely on one small dietary trial.

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What the science says

  • Injectable lentinan extends survival in advanced gastric cancer Moderate evidence

    An individual-patient meta-analysis of 5 randomized trials (n=650) of intravenous lentinan added to chemotherapy for unresectable or recurrent gastric cancer found a significant overall survival advantage (hazard ratio approximately 0.80). Lentinan is an approved injectable adjunct in Japan; this evidence says nothing about swallowing a shiitake capsule, since injected purified beta-glucan and oral extract are different exposures entirely.

  • Eating whole shiitake shifts immune markers Limited evidence

    In a 4-week randomized dietary trial, 52 healthy adults aged 21-41 ate 5 g or 10 g dried shiitake daily; both groups showed increased circulating gamma-delta T cells and NK-T cells, higher secretory IgA, and reduced CRP. It was a single small unblinded study measuring biomarkers, not infections, so it demonstrates immune modulation without demonstrating clinical benefit.

  • Cholesterol lowering by eritadenine Limited evidence

    Shiitake contains eritadenine, which lowers plasma cholesterol robustly in rodents by altering phospholipid methylation. Human data are essentially limited to small, dated, uncontrolled reports; no modern RCT establishes a lipid effect at edible or supplemental doses.

  • Mycelium versus fruiting body products Limited evidence

    Many US 'shiitake extract' capsules are grain-grown mycelium biomass, where much of the mass is residual starch from the substrate rather than fungal beta-glucan. Independent analyses of mushroom supplements repeatedly find beta-glucan content far below label implication, and alpha-glucan (starch) counted as 'polysaccharides'. Look for stated beta-glucan percentage and fruiting-body sourcing before assuming a product resembles anything studied.

Dosage & safety

Studied doseThe dietary trial used 5-10 g/day of dried shiitake (about 50-100 g fresh). Oral supplement labels typically give 500-1,500 mg/day of extract, a dose with no direct efficacy evidence. Lentinan in oncology is given intravenously at 1-2 mg once or twice weekly under medical supervision and is not comparable to any oral product.
SafetyWell tolerated as a food. The distinctive adverse effect is shiitake dermatitis — a whip-like linear flagellate rash caused by lentinan in raw or undercooked mushrooms, appearing 24-48 hours after ingestion and resolving over 1-3 weeks; thorough cooking largely prevents it. Occupational spore exposure causes hypersensitivity pneumonitis in mushroom workers. Rare reports of eosinophilia and photosensitivity with concentrated extracts. Because beta-glucans stimulate immune signaling, caution is reasonable in autoimmune disease and in transplant recipients on immunosuppressants; discuss with an oncologist before combining with cancer treatment. Not banned in sport.

How to take it

TimingTiming does not matter.
With food?Take extract with food; if you are eating the mushroom, cook it thoroughly.
Worth knowingUndercooked shiitake causes a striking whip-like flagellate rash a day or two later — thorough cooking largely prevents it.

Interactions

With medications

  • immunosuppressants and transplant medication

    Beta-glucans stimulate immune signalling, which runs counter to deliberate immune suppression. do not start it without your specialist's agreement

  • chemotherapy and immunotherapy

    Immune-modulating effects could interact unpredictably with treatment, and intravenous lentinan is a different product entirely. clear it with your oncologist before combining

Well-established interactions only — this is not a complete list. Always tell your doctor and pharmacist what you take.

Frequently asked questions

Does shiitake extract boost the immune system?

The evidence is limited: in one 4-week trial, 52 healthy adults eating 5 g or 10 g of dried shiitake daily showed higher gamma-delta T cells and secretory IgA and lower CRP, but the study was small, unblinded and measured biomarkers, not infections. Oral shiitake extract capsules have no direct efficacy evidence.

Does shiitake help with cancer?

Injected lentinan, a purified shiitake beta-glucan, has moderate evidence for extending survival alongside chemotherapy in advanced gastric cancer, but that is an intravenous drug in Japan. That evidence says nothing about swallowing a shiitake extract capsule; clear any use with your oncologist.

Why did eating shiitake mushrooms give me a rash?

Raw or undercooked shiitake can cause shiitake dermatitis, a whip-like flagellate rash from lentinan appearing 24-48 hours later and resolving over 1-3 weeks. Cooking shiitake thoroughly largely prevents it.

How do I choose a good shiitake extract?

Look for a stated beta-glucan percentage and fruiting-body sourcing: many shiitake extract capsules are grain-grown mycelium, largely residual starch, with beta-glucan far below what the label implies. Labels typically suggest 500-1,500 mg/day, a dose with no direct efficacy evidence.

Scientific references

Where to buy

Swanson Vitamins, Shiitake Mushroom Extract, 500 mg, 120 Capsules

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