Reishi is a type of mushroom used to promote health and longevity in traditional Chinese medicine and Ayurvedic medicine. Also known as the lingzhi mushroom, reishi had a red, kidney-shaped cap and finger-like spores on its underside rather than gills. The species of reishi most commonly used for medicine is Ganoderma lucidum.
Many of the purported benefits of reishi are attributed to a group of compounds called ganoderic acids, which have a similar structure to steroid hormones. Reishi is also rich in beta-glucans (which can help improve cholesterol and glucose levels).
Because of its bitter taste and woody texture, reishi is not typically used for cooking. However, it is can be used to make tea or medicinal tonics.
The term “lingzhi” was derived from the Chinese words ling (meaning spirit) and zhi (meaning plant). The Japanese “reishi” is more commonly used today, the term of which is loosely adapted from “lingzhi.”
Alternative practitioners believe that reishi is able to treat fatigue, high cholesterol, high blood pressure, and inflammation by bolstering the immune system. Others have ascribed it with “cure-all” properties that are far-reaching in their scope.
Reishi is purported to help control blood sugar levels, liver problems, immune system issues, and as an antibiotic.
Few of these health claims are supported by research. Of the studies currently available, most are limited to test tubes or small-scale animal or human trials.
Much of the current scientific focus has been placed on reishi’s effect on viral and bacterial infections, diabetes, and cancer. While some of the results are promising, none are robust enough to recommend reishi as a treatment for any medical condition.
Most research on reishi and viruses has been in laboratory settings, including herpes, HIV and Hepatitis B. While promising, the same level of control has not been seen outside of the test tube.
A 2007 study from Japan, involving 18 people, reported that a herbal remedy containing G. lucidum was able to shorten the duration of HSV-2 (genital herpes) outbreak from an average of 10.9 days to 4.0 days.
An earlier study in 1998 by the same team reported that a G. lucidum extract was able to dramatically reduced postherpetic pain in two people with an HZV (shingles) infection and two people with treatment-resistant HSV-2.
The conclusions from both of the studies are limited by their size and the lack of qualitative measures for postherpetic pain.
There is even less evidence supporting the antibacterial effects of reishi. Although there have several studies demonstrating how G. lucidum can neutralize bacteria like Staphylococcus aureus, Enterococcus faecalis, Escherichia coli, and Pseudomonas aeruginosa in the test tube, there is little proof that consuming a reishi extract will do the same.
Of the available studies, an early investigation in 1998 from Japan reported that a 2-milligram injection of G. lucidum extract in mice inoculated with E. coli improved survival rates from 33 percent to over 80 percent.
Other studies have found no effect, whether the extract was delivered orally or by injection.
The beta-glucans found in reishi are believed to aid in the management of diabetes. However, according to a 2015 Cochrane Review, any studies in humans have been of low quality and there’s little to no evidence that taking reishi will have a positive effect on cardiovascular disease risk factors in people with diabetes.
Further research is needed to substantiate these findings.
A number of lab studies have investigated reishi’s ability to stimulate the immune response, most specifically with regards to the treatment of cancer. In the lab, reishi has been shown to kill tumor cells and boost the activity of immune cells such as natural killer cells (NK), T-cells, B-cells, tumor necrosis factor (TNF), and phagocytes (which ingest other cells).
A 2016 review of studies from the University of Maryland evaluated five clinical trials involving the use of G. lucidum in treating cancer. The results of the studies were largely mixed and often contradictory.
Among some of the findings:
- An increase in the immune response, as measured by T-cells, was relatively modest in people taking G. lucidum, ranging from 2% to 4%.
- One of the reviewed studies reported an increase in NK cells; another showed no response.
- A slightly larger number of people on chemotherapy reported a better quality of life when taking G. lucidum compared to those who didn’t.
- Few side effects were reported in any of the studies.
The investigators stated the quality of the studies ranged from low to very low. Based on the current body of research, they concluded that there was insufficient evidence to justify the use of G. lucidum in the treatment of cancer.