Shiitake

What it is

Shiitake is an edible and medicinal mushroom that has been used in East Asia for over 2000 years and is the second most cultivated mushroom in the world. Its best studied compound is the polysaccharide (beta-glucan) lentinan; it also contains eritadenine and ergosterol, a precursor of vitamin D2.

What the research says

The evidence is limited. One 4-week randomised dietary study in 52 healthy young adults eating 5 or 10 g of dried shiitake daily reported changes in immune-cell markers, but it had no placebo group and measured lab markers rather than illness. Injected lentinan, a purified shiitake drug used in Japan, is where most clinical data sit: a pooled analysis of older trials linked it to longer survival in advanced gastric cancer, while a later phase III trial found no benefit. An oral shiitake extract produced no PSA responses in prostate cancer. Harms are well documented: eating raw or undercooked shiitake can cause a whip-like rash (shiitake dermatitis), and handling it can cause occupational asthma.

Evidence grade: Limited evidence.

What goes wrong

Eating raw or undercooked shiitake can cause shiitake flagellate dermatitis, an itchy linear whip-mark rash attributed to lentinan, reported in about 2% of people who eat them raw or lightly cooked. (Source 1)

• Official position, Certainty not rated.
• Size: not applicable.
• Who: People eating raw or lightly cooked shiitake.
• How long: onset around 24 hours; resolves over about 3 weeks.
• Result: About 2% of raw/lightly cooked consumers per DermNet; self-limiting.
• Funding: independent.

about 2% of people that consume the mushrooms raw or only lightly cooked

A review of shiitake lists dermatitis, itching, fever, diarrhoea and mouth ulcers with raw mushrooms, and a risk of gut obstruction if very large pieces are swallowed. (Source 2)

• Systematic review, Certainty not rated.
• Size: not applicable.
• Who: Consumers of shiitake.
• How long: not applicable.
• Result: Qualitative list; no rates given.
• Funding: not stated.

Especially when raw or uncooked mushrooms are consumed, linear flagellated dermatitis (shiitake dermatitis), pruritus, fever, diarrhea, and mucosal ulcers can develop.

Handling shiitake caused severe IgE-mediated occupational asthma in a worker, which stopped when contact was avoided. (Source 3)

• Case report, Very low certainty.
• Size: 1 patient.
• Who: Worker handling shiitake mushrooms.
• How long: not applicable.
• Result: Positive skin prick test to shiitake only; IgE-binding bands at about 15 and 24 kDa.
• Funding: not stated.

Here, we present the first European case of SM-induced occupational asthma, a disease more frequently occurring in Asia.

What the evidence supports

Eating dried shiitake daily for 4 weeks was followed by greater ex vivo proliferation and activation of gamma-delta T cells and NK-T cells, higher salivary sIgA and lower CRP in healthy young adults. (Source 4)

• Randomized trial, Low certainty.
• Size: 52 participants.
• Who: Healthy men and women aged 21-41.
• How long: 4 weeks.
• Result: gamma-delta T-cell proliferation 60% higher (p < 0.0001); NK-T 2-fold (p < 0.0001); compared 5 g vs 10 g/day with no placebo arm; outcomes are lab markers, not infections.
• Funding: not stated in the fetched abstract.

Regular L. edodes consumption resulted in improved immunity, as seen by improved cell proliferation and activation and increased sIgA production.

An individual-patient meta-analysis of 5 randomised trials found that adding injected lentinan to chemotherapy was associated with longer overall survival in advanced gastric cancer. (Source 5)

• Meta-analysis, Low certainty.
• Size: 650 patients across 5 trials.
• Who: Japanese patients with unresectable or recurrent gastric cancer.
• How long: trial follow-up.
• Result: HR 0.80 (95% CI 0.68-0.95), stratified log-rank p=0.011; no heterogeneity.
• Funding: not stated in the fetched abstract.

The overall hazard ratio (HR) was 0.80 (95% confidence interval=0.68-0.95) and there was no heterogeneity between trials.

What the evidence does not support

A later randomised phase III trial found that adding lentinan to S-1 chemotherapy did not improve overall survival and time to treatment failure was worse. (Source 6)

• Randomized trial, Moderate certainty.
• Size: 309 patients (154 S-1 alone, 155 S-1 plus lentinan)
• Who: Patients with unresectable or recurrent gastric cancer.
• How long: until treatment failure / survival follow-up.
• Result: Median OS 13.8 vs 9.9 months (P = 0.208); median TTF 4.3 vs 2.6 months (P < 0.001); ORR 22.3% vs 18.7%.
• Funding: not stated in the fetched abstract.

OS did not improve and TTF was significantly worse in the S-1 plus LNT group as compared with the S-1-only group.

An oral shiitake mushroom extract given for 6 months produced no PSA responses in men with prostate cancer. (Source 7)

• Case series, Low certainty.
• Size: 61 assessable men.
• Who: Men with prostate cancer and rising PSA (mean age 73)
• How long: 6 months.
• Result: 0 complete responses, 0 partial responses, 4 (7%) stable disease, 23 of 61 progressed; open-label, no control group.
• Funding: not stated in the fetched abstract.

SME alone is ineffective in the treatment of clinical prostate cancer.

Where the research disagrees

Whether lentinan added to chemotherapy prolongs survival in advanced gastric cancer

• Oba et al. 2009 (individual patient meta-analysis), meta-analysis of 5 older RCTs, 650 patients: The overall hazard ratio (HR) was 0.80 (95% confidence interval=0.68-0.95) and there was no heterogeneity between trials. (Source 5)
• Yoshino et al. 2016 (JFMC36-0701 phase III), RCT, 309 patients: This study showed no efficacy of LNT when combined with S-1 treatment in patients with unresectable or recurrent gastric cancer. (Source 6)

How much

• Reference intake: No recommended intake exists. Shiitake is a food and not an essential nutrient, and no reference intake for it or for lentinan was found in the sources searched. (Source 2)
• Upper limit: No tolerable upper limit has been set by any body in the sources searched. The documented dose-independent risk is dermatitis from raw or undercooked mushrooms. (Source 1)
• Studied: 5 or 10 g of whole dried shiitake eaten daily for 4 weeks (Dai et al. 2015). (Source 4)
• Studied: Shiitake mushroom extract capsules three times daily for 6 months in prostate cancer (deVere White et al. 2002). (Source 7)

A common belief, and what the research shows

The belief: Shiitake supplements are proven to boost immunity and fight cancer.

What the research shows: The immune data come mostly from lab markers in small studies, and cancer data involve injected purified lentinan alongside chemotherapy, with conflicting results. An oral shiitake extract study concluded "SME alone is ineffective in the treatment of clinical prostate cancer." and a phase III trial found "OS did not improve and TTF was significantly worse in the S-1 plus LNT group as compared with the S-1-only group."

Questions and answers

What is it?

Shiitake is an edible mushroom (Lentinula edodes) grown worldwide and used as food and traditional medicine in East Asia. It is the second most cultivated mushroom globally. (Source 2)

What does it do in the body?

Its best studied component is lentinan, a beta-glucan that acts on the immune system. In one small human diet study, eating shiitake daily for 4 weeks changed some immune-cell measurements in the blood, but no study shown here proves fewer infections. (Source 4)

Is it good or bad for you?

As a cooked food it is generally regarded as safe, and there are limited, mixed data on benefits. Raw or undercooked shiitake can cause a whip-like rash, and handling it can cause occupational asthma in sensitised workers. (Source 1)

How do you get more of it?

Studies have given people whole dried shiitake as food (5 or 10 g a day) or concentrated extracts in capsules. Lentinan used in cancer trials in Japan is a purified drug, not a supplement. (Source 4)

If it is harmful, what reduces it?

Shiitake is not something the body needs to clear. For the rash it can cause, the reaction is linked to eating it raw or lightly cooked; treatment described is symptom relief, and the rash settles within weeks. (Source 1)

Why might someone be low in it or missing it?

Does not apply. Shiitake is a food, not an essential nutrient or a body component, so there is no deficiency state. People simply do or do not eat it. (Source 2)

Which whole foods contain it or feed it?

Shiitake is itself the whole food. Like other mushrooms it contains ergosterol, a vitamin D2 precursor, which makes mushrooms a non-animal source of vitamin D precursors. (Source 2)

What happens if you do not have it?

Nothing is known to happen. Shiitake is not essential, and no study found links not eating it to any deficiency or disease. (Source 2)

We searched: Searched PubMed-indexed reviews and a 2024 review of Lentinula edodes composition; no deficiency concept exists for a non-essential food.

How can you test for it?

There is no test for shiitake 'levels' in the body. Allergy to shiitake can be investigated with skin prick testing and IgE testing, as in a published occupational asthma case. (Source 3)

References

1. DermNet (New Zealand). Shiitake flagellate dermatitis. 2016. Read the source
2. Journal of Fungi. Medicinal Mushrooms as Multicomponent Mixtures—Demonstrated with the Example of Lentinula edodes. 2024. DOI 10.3390/jof10020153. Read the source
3. International Journal of Occupational Medicine and Environmental Health. Shiitake mushroom (Lentinus edodes): A poorly known allergen in Western countries responsible for severe work-related asthma. 2014. DOI 10.2478/s13382-014-0296-2. Read the source
4. Journal of the American College of Nutrition. Consuming Lentinula edodes (Shiitake) Mushrooms Daily Improves Human Immunity: A Randomized Dietary Intervention in Healthy Young Adults. 2015. PMID 25866155, DOI 10.1080/07315724.2014.950391. Read the source
5. Anticancer Research. Individual Patient Based Meta-analysis of Lentinan for Unresectable/Recurrent Gastric Cancer. 2009. PMID 19596954. Read the source
6. European Journal of Cancer. Randomised phase III study of S-1 alone versus S-1 plus lentinan for unresectable or recurrent gastric cancer (JFMC36-0701). 2016. DOI 10.1016/j.ejca.2016.06.012. Read the source
7. Urology. Effects of a mushroom mycelium extract on the treatment of prostate cancer. 2002. PMID 12385925, DOI 10.1016/S0090-4295(02)01856-3. Read the source