I realized recently that there is one health supplement that I take every day, based entirely on hearsay and expert advice, but not on my own research. Not very ‘Healthy But Smart’, I have to admit. Not only do I take shiitake supplements, but I also include them in my diet. 

Worst of all, shiitake is one of my more expensive supplements. I have to admit that I don’t mind spending money on my health but I do mind making uninformed decisions.

I guess that I agree with Socrates that ‘the unexamined life is not worth living’ or in my case ‘the unexamined supplement is not worth taking’. Or is it?

What Are Shiitake Mushrooms?

Shiitake mushrooms or Lentinula edodes is a type of fungus. It is also known as champignon noir and champignon parfume. Shiitake is the second leading selling mushrooms worldwide and the third most widely grown edible mushroom worldwide (1).

This makes me feel vaguely better as I am pretty sure that the vast majority of these consumers never did due diligence before spending their hard-earned dollars either.

The popularity of shiitake is thought to be due to its reputed medicinal properties and unique taste and texture The taste is sometimes described as umami which is a Japanese term for tastes that are neither sweet, sour, salty or bitter.

The key bioactives in shiitake include polysaccharide lentinan, eritadenine, shiitake mushroom mycelium, culture media extracts, and fiber.

It is used as an immune booster, lipid-lowering agent, mouthwash and for obesity. I take shiitake primarily as an immune booster as I work with patients with infectious diseases on a daily basis and want to stay healthy. At least, that’s the theory.

Mushroom extracts are also used in upmarket skincare creams (oops, I have some of those in my bathroom too).

There are 372 shiitake products for sale on Amazon including powder, capsules, creams, growing kits and even crisps (I think that crisps are possibly the only shiitake product that I don’t have).

Is There Any Research?

There are 734 publications that include 15 clinical trials for the search term ‘shiitake’. Using the more formal search term ‘Lentinula edodes’ gives us 827 publications and 12 clinical trials.

Two of the clinical trials are in broiler chickens which is hardly going to be the basis for my future buying decisions.

To put this into context, the research basis for shiitake is comparable to maitake mushrooms which have almost 400 publications and 7 clinical trials, and Chaga mushrooms that have had no human clinical trials.

Do Shiitake Mushrooms Fight Obesity?

There are no human clinical trials to guide us here but there is one relevant non-human clinical trial publication. Though, you could argue that buying decisions based on broiler chickens are better than decisions based on urban myths or clever marketing.

The total fat deposition was shown to be 35% less (which was statistically significant) in rats fed a high-fat diet along with shiitake mushrooms (2). The study also found that increasing doses of shiitake had greater effects on weight loss.

This is certainly interesting. The cynic in me thinks that it is even more interesting to think that this study was done back in 2011 and there has been no follow up human study.

Anything to do with weight loss and especially foods that can promote weight loss is automatically a hot topic. Even more attractive than weight loss is the ability to eat fatty foods while avoiding weight gain. Why has no one seized this opportunity?

Bottom Line

There is no human clinical proof that shiitake helps with weight loss or obesity.

Does it Support Immune Function?

sneezing

I really hope to find some overwhelmingly positive evidence here to justify my total lifetime expenditure on shiitake based products.

Researchers from Gainesville, Florida, studied whether shiitake mushrooms (whole or dried) could affect immunity (3). The study enrolled 52 healthy volunteers who ate either 5 or 10 gm of shiitake per day for 4 weeks.

At the end of the 4 weeks of intervention, statistically significant increases in T cells, natural killer cells, IgA (gut immunity), IL-4, IL-10, and TNF were noted. No changes in IL-6, IL-17 and gamma interferon were noted.

Does this mean that I am justified in my expenditure?

Each part of the immune system works in collaboration with the other parts and each part of the immune system has a unique role. This means that increases in one part of the immune system might increase immunity against one specific bug and not another.

Equally, an increase in one part of the immune system without a complimentary increase in a co-factor could limit the benefit of the apparent increase. Finally, increases in certain parts of the immune system can worsen allergies or autoimmune disorders which again means that it is way too simplistic to assume that increases in immunity would be good for everyone.

Studies such as this are useful but very limited as they don’t tell us what clinical significance (if any) these changes make.

There are other studies that are also limited to laboratory data. Korean investigators looked at the effects of arabinoxylan derived from shiitake in 80 healthy study participants (4).

The study participants were either randomized to take 3gm of rice bran fortified with shiitake or 3 gms of placebo for 8 weeks. The study found significantly increased interferon production in the rice bran group as compared to the placebo group.

The rice bran had no effect on natural killer cells, tumor necrosis factor or a range of interleukin cytokines.

Lentinan derived from shiitake was studied in HIV positive patients in San Francisco and New York (5). A non-statistically significant trend towards improvement in T-helper of CD4 cells was noted. This study was published in 1998 and followed the patients for 8 weeks.

This means that the study was conceived and designed before 1998 and during a time when we had very limited HIV drugs. Since then, a range of highly effective anti-HIV drugs has come to market. This may explain why no follow-up studies have been done on this one.

Norwegian researchers found that shiitake supplementation resulted in a significant increase in the number of B cells and natural killer cells in a double-blind, crossover, placebo-controlled trial in 42 elderly adults (6).

Bottom Line

Here is my own mini-systematic review of things. There are 4 small clinical studies of relevance. T-cells increased in two studies (one increase was not significant).

Natural killer cells increased in two studies but not in a third study and were not studied in the fourth study. Of the two studies reported on interferon, one showed benefits while the other did not.

None of the studies lasted longer than 8 weeks. None of the studies correlated the blood-work with any clinical outcomes. Sadly, I have to admit that I am taking a supplement that is not based on any clinical evidence.

That being said, I think that there is at least evidence that shiitake mushrooms have some role to play on the immune system.

Does It Destroy Cancer Cells?

We have a very limited bank of human clinical trial data to look at here.

Shiitake was found to be ineffective at lowering prostate-specific antigen when taken over 6 months in men with prostate cancer (7).

Active Hexose Correlated Compound (AHCC) derived from shiitake was found to be safe in a study of 26 healthy volunteers (8).

The rationale for the study was the fact that AHCC is of interest in hepatocellular cancer. This study looked at healthy volunteers and was not designed to look at anti-cancer effects.

Shiitake was found to improve the quality of life and natural killer cell activity in 6 cancer patients (9). The big problem with this study is the fact that it only enrolled 7 patients and these patients did not even represent the same patient population: three had breast cancer, two had gastrointestinal cancer and two were receiving treatment to prevent recurrence of gastrointestinal cancer.

Bottom Line

There is too little data to make any sensible decision on shiitake and cancer.

Does it Support Cardiovascular Health?

There is one vaguely related study here (10).

The study looked at shiitake extract in healthy men who were asked to run for 105 minutes. No effects were noted on immune or inflammatory cells but an antioxidant effect was noted. I am aware that this is not exactly a hardcore cardiac study but it is as close as I could get.

Bottom Line

Shiitake mushrooms don’t do anything for heart health.

Does It Have Antimicrobial Properties?

I am secretly hoping that the answer to this question is an overwhelming YES.

There is an interest in the potential benefits of shiitake in the agricultural sector to improve animal growth and profits. One study found that shiitake mushroom supplements in feed helped speed up recovery from Bordetella lung infection in mice (11).

The mushroom supplement also helped prevent infection-induced weight loss in these mice. Not that anyone is planning on eating mice to get these benefits. This was just a pilot proof of concept study.

Japanese investigators studied shiitake in cells infected with influenza and found anti-viral activity via inhibition of cell growth (12).

They then took the line of inquiry to the next level by checking what would happen if influenza-infected mice were given nasal or oral shiitake. The intra-nasal or oral shiitake helped reduce the severity of disease and also improved survival time in the mice.

The results they found were due to a complex interplay between improved immunity and a direct anti-viral effect on infected cells.

Bottom Line

Maybe I am just unwilling to be wrong, but it is possible that shiitake has some immune-boosting or anti-infective effects. But if I am honest with myself and I stick to the clinical data then I have to admit that my belief in the anti-infective effects of shiitake is unfounded.

Does It Boost Brain Function?

brain function

Again I have to resort to the only vaguely related study here (13). After all, there is only one semi-relevant study to go on. The study looked at the interaction between gabapentin and shiitake mushrooms. Gabapentin is a medication used to treat epilepsy and nerve pain.

This study showed that shiitake mushrooms could increase the rate at which the kidneys cleared gabapentin from the body but despite this, there was no significant increase in the blood levels of gabapentin.

I totally get that if this were an exam that I would fail as this research paper is hardly relevant to the question of shiitake mushrooms and brainpower. But with only one study to go on, what can I do?

Bottom Line

Shiitake have not been proven to boost brainpower.

Does It Provide Vitamin D?

Mushrooms contain high levels of pro-vitamin D (14). Exposure to sunshine converts pro-vitamin D to vitamin D2, D3, and D4 which makes sun-exposed mushrooms a good source of vitamin D for humans.

This is known as photobiology. Cooked and salted shiitake mushrooms contain 28 IU of vitamin D and 0.7 micrograms of vitamin D2 and D3 per 100gm (15). The recommended daily allowance (RDA) for vitamin D is 600 IU (16).

To put this into context, a 100ml glass of Tropicana orange juice fortified with vitamins gives 41 IU (17).

Bottom Line

Shiitake mushrooms are a good source of vitamin D but certainly cannot claim to be the best source of the sunshine vitamin.

Does It Promote Skin or Mouth Health?

If you knew how much my mushroom night cream cost me, you would be silently praying that there is a huge randomized clinical trial which showed that shiitake mushroom in a jar reduces wrinkles, promotes elasticity and maybe even prolongs life (and helps you win the lotto).

That would be wishful thinking. Here is the science.

Shiitake induced dermatitis is well described and was first reported in the medical literature in 1977 (18). This typically occurs after eating raw or poorly cooked shiitake mushrooms.

The appearance of dermatitis has been likened to the wounds inflicted by self-flagellation during the Middle Ages. It is caused by a toxic reaction to lentinan which is a polysaccharide found in the mushrooms that decompose on heating.

Dermatitis can be associated with changes in a range of blood tests including liver tests. Am I really paying money to run the risk of looking like a Medieval victim of torture?

Shiitake extract mouthwash tested over two weeks against a standard mouthwash showed that shiitake mushrooms have an anti-caries effect (as determined by acidity check, plaque scores, and antimicrobial composition) (19). However, it was not as effective as a standard proprietary mouthwash.

Bottom Line

I was foolish to spend my hard-earned cash on mushroom creams, lotions, and potions.

Are Shiitake Mushrooms Safe?

Like all mushrooms, shiitake should be properly cooked to release vitamins, minerals, and proteins in addition to killing potential carcinogens and toxins.

Shiitake mushroom powder resulted in eosinophilia in blood and feces along with gastrointestinal symptoms in 5 out of 10 study subjects (20). The eosinophilia and symptoms settled on discontinuation of the mushroom supplement.

Eosinophilia is considered to be a hallmark of allergy and this report certainly raises concerns about allergic reactions to mushroom supplements. It also raises concerns about the use of mushroom supplements in people with a history of allergies or auto-immune disorders.

To avoid further humiliation, let’s not revisit the shiitake dermatitis again, but it is a side effect.

Conclusion

I often wonder who reads these articles. What actually happens when I press ‘publish’ and the article goes out into the ether.

I am a fan of Agatha Christie’s ‘Miss Marple’ who believed that she could understand humankind and solve mysteries based on her in-depth knowledge of her own life.

If that is the case, then I can assume that the people reading this article will be similar to the patients that I have seen over many years in clinical practice. The mom of young children who is trying to multi-task with limited sleep.

The business executive trying not to succumb to overwork. The person trying to come to terms with a new diagnosis. The gym lover who just wants to look good and be super healthy. The woman trying to conceive (TTC).

As I write, I imagine any of these people standing in the aisle of Wholefoods trying to decide between the umpteen choices of foods, supplements, and vitamins. I hope that articles like this will make it easier for readers to make those consumer choices.

If you have a limited budget, then I would walk past the mushroom section as you will find other functional foods or food-based supplements with a better scientific track record for whatever health or wellness concern that you may have.

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