Veteran broadcaster Sheila Dillon, who was diagnosed with cancer of the bone marrow in 2011, shared some personal information while presenting a recent episode of BBC Radio 4’s The Food Programme. She began taking mushroom supplements after discovering that patients in Japan were given them to help deal with the effects of radiotherapy and chemotherapy, and that there was, she told listeners, “a good deal of evidence” that they did. The last time she saw her oncologist, he told her she was “in danger of becoming a super-responder”.
Dillon said she did not know if there was a link between the supplements and her successful treatment. She is, nonetheless, far from alone in being open to the idea that fungi could have far more potential to treat health conditions than is acknowledged in mainstream western medicine. One market research company estimates the global functional mushroom market will grow from $8bn in 2020 to $19.3bn in 2030. High-street chain Holland & Barrett stocks 17 different fungi supplement products. “In the last two months, we’ve seen a 70% increase in the quantity of mushroom products purchased,” says Rachel Chatterton, head of food at the company, “and we don’t expect the ‘shroom boom’ to slow any time soon.”
Dozens of claims are made for medicinal mushroom products. The Bristol Fungarium, for example, sells extracts of fungi that it says relieve anxiety, prevent wrinkle formation, stabilise blood pressure and ease hot flushes. From heart health and type 2 diabetes to allergies and cancers, the list of ailments that mushrooms are said to alleviate is long. But are these claims supported by scientific evidence? Or are medicinal mushrooms just the latest fad?
In a former grain barn on a hill at the end of a country lane in north Somerset, groups of bulbous, cream-coloured young reishi heads rear up on dark red stalks, alongside rows of giant cauliflower-like lion’s mane poking out from metal shelving units. This is the Bristol Fungarium’s growing room. Next door, seven employees are hard at work turning fungi into tinctures and packaging them to fulfil orders.
Outside, builders are constructing a second growing room to enable the company to double its production. In the last year, sales totalled about £1.4m, according to Tom Baxter, who founded the business in 2019. He expects this to double over the next 12 months.
About half of the Bristol Fungarium’s revenue comes from lion’s mane, which, according to a company leaflet, is beneficial for patients with mild dementia, has potential in alleviating inflammatory bowel disease (IBD) and “is purported” to help manage attention deficit hyperactivity disorder symptoms. Evidence to support these claims from human trials is scant, however, though lion’s mane extracts have been shown to stimulate the growth of nerve cells in Petri dishes and rodents.
“The human body is a galaxy of trillions of cells that are interacting with one another and microbes in our microbiome,” says Prof Nicholas Money, a mycologist at Miami University in Ohio, who published a review on medicinal mushrooms in 2016. “Preliminary cell and animal studies are an interesting starting point, but extrapolating effects seen in cultured human cells to treatment of serious conditions is beyond absurd.”
Baxter acknowledges that many of the claims made for medicinal mushrooms are based on extrapolating from cell cultures. He does, however, highlight two clinical trials of lion’s mane, one published in 2009, that found extracts of the mushroom improved cognitive test scores in older adults with mild cognitive impairment, and another that suggested benefits for those with mild Alzheimer’s disease. In the first trial, just 15 participants took the supplements and in the second study, only 20. Both also involved researchers working for companies that sell mushroom supplements.
Many health claims have been made for reishi, dating back more than 2,000 years, including that it can boost the immune system and gut health, alleviate fatigue and improve sleep. Some researchers also say cell culture and animal studies suggest it can promote anti-cancer activity in immune cells and suppress cancer cell growth. “Reishi can activate the body’s natural killer cells that can target cancer cells and increase apoptosis, or programmed cell death, in cancer cells,” says Giuseppe Venturella, a botanist and mycologist at the University of Palermo in Italy.
While most research on the fungus has been in cell cultures, one review identified 26 human trials of reishi, including some that found benefits for patients with high blood pressure, type 2 diabetes, heart disease, hepatitis B and cancer. Its author highlighted that these findings were often undermined by participants knowing they were receiving the treatment, small sample sizes and a lack of confirmatory follow-up work.
Extracts of turkey tail have been used as mainstream cancer treatments since the 1970s in Japan and 1980s in China. “Turkey tail is an immune system regulator,” says Baxter. “It’s very good for lung cancers and a lot of different cancers.”
A group led by Dr Karen Pilkington, a research evaluation expert at the University of Portsmouth, reviewed seven randomised controlled trials examining whether PSK (polysaccharide-K), an extract of turkey tail, reduced the side effects of radiotherapy or chemotherapy in colorectal cancer patients. The group found the small numbers of study participants, a lack of placebo control groups and the possibility that patients might report side effects differently because they knew they were taking PSK meant any benefits were unclear.
Chaga, which grows on birch trees and resembles burnt charcoal, prevents wrinkles, helps counter IBD and fights bacterial and viral infections, according to some of those that sell it. Cordyceps militaris, the “zombie fungus” that inspired the HBO series The Last of Us, is reported to improve exercise performance, act as an antidepressant and boost female libido. In none of these cases however, are such claims supported by well-designed clinical trials.
Under UK law, food labelling cannot “attribute to any foodstuff the property of preventing, treating or curing a human disease”. Such claims fall under medicines regulations and require marketing authorisation from the Medicines and Healthcare Products Regulatory Agency (MHRA). A spokesperson for the MHRA said it had received no marketing applications for products containing lion’s mane, turkey tail, reishi, cordyceps, chaga or shiitake, and that a number of retailers had been warned about making health claims for mushroom products and use of the term “medicinal mushrooms”.
While medical drugs are based on specific purified compounds that have been comprehensively tested for safety and efficacy, medicinal mushroom supplements can contain hundreds of different chemicals. The levels of active compounds that the health effects might be based on can also vary depending on a number of factors, including the age of cultivation, what the mushroom are grown in and whether extracts are from mushrooms’ fruiting bodies or their root-like mycelia. It is also hard to know what doses are contained within many mushroom-based products. Tests have shown that sometimes the species of fungi advertised on labels are not even present in the products.
It seems the vast majority of health claims made for mushrooms are unsupported by good-quality human trials. Even sceptics acknowledge, however, that absence of evidence is not evidence of absence. Many drugs derived from fungi – including the antibiotics penicillin and cephalosporins, and cholesterol-lowering lovastatin – are already in use. Advances in genome sequencing and techniques for mining genetic information have led to hope that more of the huge range of compounds fungi produce can be isolated, purified and used in specific doses to treat human disease.
Money says that some of the claims being made currently for medicinal mushrooms are “without scientific foundation and amount to little more than snake oil”. However, “fungi have rich chemical relationships with other organisms in their environments, and I’m sure they do contain many more useful compounds,” adds Money, whose book Molds, Mushrooms and Medicines will be published in March. “We need to see the use of advanced scientific methods to identify those that are genuinely beneficial for alleviating or treating human illnesses.”
