WARNING!
This is an older article that may not reflect Dr. Mercola’s current view on this topic. Use our search engine to find Dr. Mercola’s latest position on any health topic.
Mushroom lovers will be pleased to know that researchers studying the earthy fungi continue to find benefits for health in them. One of the most popular mushrooms is the shiitake (Lentinus edodes), which grows on decaying hardwood trees such as oaks, maples, chestnuts, hornbeams and ironwoods in their natural environment, but are commercially grown elsewhere.1
Recreating the same environmental conditions has allowed growers in the U.S., as well as Canada, Singapore and China, to proliferate the brown-capped delicacies. According to Market Research Future,2 the shiitake mushroom forecast through 2023 is projected to reach $35.4 billion, due in part to its robust use in the food industry, although nutritional and medicinal market shares are also thriving.
Shiitake mushrooms are very versatile for a variety of dishes. They're great as a filling for sandwiches and diced to use in soups, casseroles and stir-fries. A favorite method of preparation is to sauté them in a skillet, which is easy and quick with coconut oil or avocado oil, adding a bit of Himalayan salt (depending on the amount you're making) and a few pinches of select herbs and garlic.
Not only are they highly sought after for their buttery flavor, which becomes rich and smoky when dried, shiitakes are loaded with vitamins, minerals and compounds that are remarkably health beneficial, even though they are close to 90% water.3
One study notes that shiitake mushrooms have a long history of use in folk medicine for treating "tumors, flu, obesity, high blood pressure, sexual dysfunction, aging, heart disease, diabetes, liver ailments, respiratory diseases, weakness and fatigue."4
Rather than killing cancer cells directly, a sugar molecule in shiitakes called lentinan instead enhances your immune system, which may help slow the growth of tumors.5 According to the International Journal of Microbiology:
"Shiitake mushroom has been used for many years to investigate functional properties and to isolate compounds for pharmaceutical use; this is because of its positive effects on human health. It has been utilized to alleviate the common cold for hundreds of years and some scientific evidence has supported this belief …
It has been reported that lentinan enhances host resistance against infections by bacteria, fungi, parasites, and virus; it also promotes nonspecific inflammatory responses, vascular dilation, hemorrhage-inducing factors activation, and generation of helper and cytotoxic T cells."6
Studies on shiitake mushroom compounds lentinan and β-glucans
The nutrients multiply in shiitakes after about 80% of the water is extracted or they otherwise dry out. In fact, that's the most popular form for their consumption to get the greatest nutritional value.7 A study in 20158 found that whole, dried Lentinula edodes (shiitake) mushrooms could improve human immune function. Participants included 52 healthy adults who ate 5 to 10 grams of the mushrooms daily for four weeks.
At the end of the study, the scientists found that T cells were activated and "proliferated in huge numbers"9 to improve immunity (including gut immunity) and possibly decrease inflammation. Interleukin, which facilitates cell communication and regulates cell growth to optimize immune responses,10 was also increased, as was tumor necrosis.
One of the most studied aspects of shiitakes involves cancer and other serious diseases that are causing concern in part because they're continuing to flourish.11 Compounds in these rather nondescript fungi were found to effectively treat or protect against:
- Cancer,12 including breast cancer,13 certain colon and bladder cancer cells,14 and tumors,15 inhibiting cancer growth and inducing apoptosis16
- Infectious diseases17
- High blood pressure18
- Diabetes19
- Heart and liver problems20
Several beta-glucans and the lentinan from shiitake mushrooms exhibited "marked anticarcinogenic activity, immunity-stimulating effects and may participate in physiological processes related to the metabolism of fats in the human body,"21 another study showed.
Shiitakes and other mushroom varieties also contain antioxidants other plants or fungi do not possess, such as ergothioneine, addressed by the journal Molecules as "Concentrated in mitochondria, suggesting a specific role in protecting mitochondrial components, such as DNA."22
Specific and overall benefits of shiitake mushrooms
Scientists have established that the antioxidant and antimicrobial properties, as well as the many phenolic contributors, of shiitake mushrooms are cancer preventative and immunity boosting.
But there's also evidence of cognitive benefits, as people who ate mushrooms twice or more per week, compared to those who ate them less than once per week, were found to have a 50% lower risk of mild cognitive impairment.23,24 Some of the most dramatic benefits are for specific areas of your body, as well as your entire system overall. These include:
• Bone health — Vitamin D in edible mushrooms helps absorb calcium, which helps strengthen bones. In fact, exposing mushrooms to ultraviolet (UV) light increases the vitamin D levels. An animal study found that mice fed UV-exposed mushrooms and calcium, compared with other mice deprived of vitamin D and calcium, exhibited higher bone density.25
• Cancer-fighting properties — A review of five edible mushrooms — button (Agaricus bisporus), A. blazei, oyster mushrooms (Pleurotus ostreatus), maitake (Grifola frondosa) mushrooms, as well as shiitakes — revealed all share anticancer compounds such as polysaccharides, proteoglycans and steroids.26
Lentinan, a polysaccharide in shiitakes which can be used along with chemotherapy to improve survival rates even in advanced cases,27 reportedly activates your immune system to halt the proliferation of leukemia cells.
• Antimicrobial properties — One of the most concerning problems related to health care today involves the common use of antibiotics and resulting resistance, even when other modes of treatment may be more appropriate. An example is tuberculosis, which researchers have found may be remedied by the antimicrobial properties of the lentinan in shiitake mushrooms.28
• Dental health — A 2016 study notes a recent upsurge of interest in mushrooms, particularly shiitakes, as a caries preventive food. It notes a number of ways its compounds exert antimicrobial activity, due to such compounds as adenosine, erythritol, copalic acid, carvacrol and many more:
"Anticariogenicity can be attributed to the induction of the detachment of cariogenic microorganisms from hydroxyapatite, changes in cell surface hydrophobicity, bactericidal activity, and disruption of signal transduction in Streptococcus mutans as proved through various in vivo and in vitro studies.
Apart from these benefits, it has tremendous potential to be used as an antioxidant, anticancer, antigingivitis, antifungal, and antiviral agent."29
Shiitake mushroom nutrients and possible side effects
Another study30 outlines additional nutrients in shiitake mushrooms, including vitamins B1, B2, B12 and vitamin C, noting the "highest level of vitamin D of any plant food." It also notes the presence of niacin, "proteins, fats, minerals and β-glucans polysaccharides (b-glucans)" … which additional studies show may "increase the resistance of the intentinal mucosa to inflammation and inhibit the development of intestinal ulcers." Further, a 2014 study reported:
"Mushrooms have a great nutritional value and present medicinal molecules including polysaccharides, terpenoids, sterols and lipids that participate actively in several human disorders and modulate mechanisms involved in the immune system regulation."31
It's also helpful to note that handling and/or eating shiitake mushrooms that are either inadequately cooked or raw may cause a skin reaction or rash with an appearance of long thin stripes, due to the lentinan content, as outlined in a study in the journal of the Brazilian Society of Dermatologists, "Shiitake Dermatitis."32 However, the cases are characterized as rare: one found in Brazil and another in Germany.
Researchers in another study33 referenced symptoms of hypersensitivity pneumonitis, an inflamed lung condition due to fungus dust; pruritus or an itch; and eosinophilia, which Mayo Clinic describes as an abnormally high level of a certain type of white blood cell that may indicate a parasitic infection.34