Reishi and Diabetes: What the Research Shows
- , by SANUSq Research team
- 13 min reading time
Search for reishi for diabetes and you will find bold promises about blood sugar. Reishi has a long and impressive reputation, and diabetes is one of the conditions it is most often linked with. This is exactly the kind of topic where it pays to separate tradition from what has actually been tested in people, and from what can honestly be concluded.
Reishi in brief
Reishi (Ganoderma lucidum, known as lingzhi in China) is a woody, shelf-like mushroom that has been used in East Asia for more than 2,000 years. It is usually grouped with the adaptogens, and traditionally it has been taken as a general tonic rather than for one specific purpose.
Its best-studied components are polysaccharides, particularly beta-glucans, and triterpenes, the compounds that give reishi its distinctive bitter taste. Most of the research interest, including the interest in blood sugar, centres on these two groups.
Why reishi and blood sugar became linked
The idea did not come from nowhere. Laboratory and animal studies have shown that certain Ganoderma lucidum polysaccharides can influence glucose metabolism and markers of inflammation. Those findings are genuine, and they were a fair reason to test the mushroom in people.
But an effect seen in cells or in rodents tells us very little about what will happen in a person living with type 2 diabetes. The history of medicine is full of promising laboratory leads that did not hold up once they reached properly controlled clinical trials. For reishi and blood sugar, that is the step that matters, so it is where we should look.
Reishi for diabetes: what human trials found
The question has been examined in an independent systematic review, which is the most reliable way of weighing up the trials that exist.
A Cochrane review by Klupp et al. (2015) identified five trials with 398 participants. The three that could be used in the analysis compared Ganoderma lucidum (1.4–3 g a day) with a placebo for 12 to 16 weeks, and all of their participants had type 2 diabetes. Reishi was not associated with a meaningful change in HbA1c (glycated haemoglobin), fasting glucose, cholesterol, blood pressure or body-mass index. The authors concluded that the evidence does not support using reishi for cardiovascular risk factors in people with type 2 diabetes, and noted the small number of trials and their methodological limits.
The largest of those trials was published in full a year later, and its result was just as clear.
In a double-blind, placebo-controlled trial, Klupp et al. (2016) gave 84 adults with type 2 diabetes and metabolic syndrome 3 g a day of Ganoderma lucidum, with or without cordyceps, or a placebo for 16 weeks. The mushroom had no effect on HbA1c or fasting plasma glucose, nor on any of the secondary measures, and the researchers concluded that the results do not support its use for cardiovascular risk factors in diabetes or metabolic syndrome.
It is worth being plain about this. These are not encouraging early results that can be dressed up as "promising, more research needed". They are negative findings on the very outcome most readers care about: blood sugar and the risk factors that come with it. The trials were few and imperfect, so the door is not closed to future research, but as things stand reishi has not shown an effect on blood sugar in people.
What this means in practice
Type 2 diabetes is a medical condition that needs monitoring and care from a doctor or diabetes team. No supplement is a substitute for prescribed treatment, for regular HbA1c checks, or for the measures with solid evidence behind them: diet, physical activity and weight management.
Three practical points follow:
- Never change or stop your diabetes medication because you have started a supplement. Any change to treatment should be decided with your doctor.
- Talk to your doctor before adding reishi if you take glucose-lowering medicines such as insulin or sulfonylureas. Combining any supplement with these medicines may make blood sugar harder to keep steady, and the risk of hypoglycaemia (low blood sugar) is the main concern.
- Keep up your usual self-monitoring. Taking something "natural" is never a reason to check your glucose less often.
Reishi mushroom benefits with stronger evidence
None of this means reishi has nothing to offer. The picture is simply different from what its reputation suggests. The most studied area is the immune system, where reishi polysaccharides show activity on several immune markers.
Gao et al. (2003) gave 34 people with advanced cancer a Ganoderma lucidum polysaccharide extract for 12 weeks and reported changes in several immune measures, including higher natural killer cell activity and shifts in some cytokines. There was no placebo group, and these were laboratory markers in a very specific group of patients, not evidence of a clinical benefit in the general population.
More recent work in healthy adults points in a similar direction, again at the level of laboratory measures.
In a randomised, double-blind, placebo-controlled trial, Chen et al. (2023) gave healthy volunteers aged 18 to 55 a beta-glucan derived from reishi for 84 days. Compared with placebo, the beta-glucan group showed increases in several immune cell counts, including T-lymphocytes and natural killer cells. The product was well tolerated, with no significant changes in kidney or liver function markers.
Then there is reishi's most consistent traditional use: as a calming mushroom, taken in the evening and associated with rest. This use is old and widely described, but it rests on tradition and preliminary research rather than on robust trials. Saying so is more useful than presenting it as proven.
How reishi is taken
The fruiting body is too tough and too bitter to eat as it is. Reishi is therefore sold as a decoction (a long-simmered tea), a powder, capsules or concentrated extracts. A few quality markers apply to every format:
- Which part is used. The fruiting body and the mycelium (the root-like network grown on a substrate) are not equivalent.
- A stated beta-glucan content, rather than a vague "total polysaccharides" figure, which can include starch from the growing medium.
- Testing for heavy metals. Mushrooms readily accumulate them from their environment, so a reputable supplier should test each batch.
A product that says nothing about any of these already tells you something.
How much, and for how long
The clinical trials in people with diabetes used around 1.4–3 g a day for 12 to 16 weeks. That gives a sense of scale, but it is not a recommendation. In practice, amounts vary widely depending on whether a product is whole mushroom powder or a concentrated extract, and the two are not comparable gram for gram. Follow the manufacturer's label, and judge any product over several weeks rather than a few days.
Reishi safety and precautions
In trials, reishi has generally been well tolerated, with mild side effects such as a dry mouth or digestive discomfort.
Wicks et al. (2007) gave 16 healthy volunteers 2 g of reishi extract or a placebo twice a day for 10 days and found no adverse effects on heart tracings, blood counts, blood chemistry or urine tests. The study was small and short, and the authors called for longer safety trials.
There are, however, situations where extra care is needed.
Blood thinners and surgery
Reishi may affect how platelets clump together, which is one step in blood clotting.
In an early study, Tao and Feng (1990) found that a water-soluble reishi extract inhibited platelet aggregation in the laboratory, and that platelet aggregation was reduced in 33 patients with atherosclerotic disease after they took 1 g of reishi three times a day for two weeks.
If you take an anticoagulant such as warfarin or an antiplatelet medicine such as aspirin or clopidogrel, speak to your doctor before taking reishi. For the same reason, tell your surgeon or dentist if you take it before a planned operation; they may advise stopping it beforehand.
The liver
Rare cases of liver injury have been reported in people taking reishi, mainly in powdered form.
Wanmuang et al. (2007) described a fatal case of acute hepatitis in Thailand and noted an earlier case from Hong Kong; in both, the problem appeared after one to two months of reishi powder, and both patients were also taking other medicines. Guedikian et al. (2023) reported acute liver injury in a man who had taken reishi powder with alcohol; he recovered fully within two weeks.
Case reports cannot show how often this happens, and it appears to be uncommon. Even so, stop taking reishi and see a doctor promptly if you notice yellowing of the skin or eyes, dark urine, unusual tiredness or pain in the upper right abdomen. If you have liver disease, ask your doctor first.
Other situations
Seek medical advice before taking reishi if you are on immunosuppressant medicines, have had an organ transplant, or are pregnant or breastfeeding. In each of these cases, your doctor's advice should come before you start, not after.
The bottom line
Reishi is a mushroom with a long history of use and active research into its polysaccharides. On diabetes specifically, the human trials available do not support its use, and that is more useful to know than a promise. If blood sugar is what brought you here, the things that make the difference lie elsewhere: what you eat, how active you are, your weight and regular medical follow-up. Reishi deserves to be seen for what it is, a traditional mushroom with a modest place in the current evidence.
Frequently asked questions
Does reishi lower blood sugar?
Human trials have not shown that it does. A Cochrane review of trials in people with type 2 diabetes found no meaningful change in HbA1c or fasting glucose, and a 16-week placebo-controlled trial found no effect on either measure.
Can I take reishi with diabetes medication?
Not without speaking to your doctor first. Adding a supplement to glucose-lowering medicines may make blood sugar harder to keep steady, and low blood sugar is a particular concern with insulin and sulfonylureas. Never change your diabetes medication without your doctor, and keep up your usual monitoring.
Is Ganoderma lucidum the same as reishi?
Yes. Ganoderma lucidum is the scientific name, reishi is the Japanese name and lingzhi is the Chinese name for the same mushroom.
What are the best-documented reishi benefits?
The most studied area is the immune system, where reishi polysaccharides have shown effects on immune markers in laboratory work and a few small clinical studies. Its traditional use as a calming mushroom has not been confirmed by robust trials.
How do I choose a good-quality reishi?
Check which part of the mushroom is used (fruiting body or mycelium), look for a stated beta-glucan content rather than total polysaccharides, and choose a supplier that tests for heavy metals.
Who should avoid reishi?
Take extra care, and ask your doctor first, if you use blood thinners or antiplatelet medicines, have surgery planned, have liver disease, take immunosuppressants, or are pregnant or breastfeeding.
References
- Klupp NL, Chang D, Hawke F, Kiat H, Cao H, Grant SJ, Bensoussan A. Ganoderma lucidum mushroom for the treatment of cardiovascular risk factors. Cochrane Database of Systematic Reviews. 2015;2015(2):CD007259. PMID 25686270
- Klupp NL, Kiat H, Bensoussan A, Steiner GZ, Chang DH. A double-blind, randomised, placebo-controlled trial of Ganoderma lucidum for the treatment of cardiovascular risk factors of metabolic syndrome. Scientific Reports. 2016;6:29540. PMID 27511742
- Gao Y, Zhou S, Jiang W, Huang M, Dai X. Effects of ganopoly (a Ganoderma lucidum polysaccharide extract) on the immune functions in advanced-stage cancer patients. Immunological Investigations. 2003;32(3):201–215. PMID 12916709
- Chen SN, Nan FH, Liu MW, Yang MF, Chang YC, Chen S. Evaluation of immune modulation by β-1,3; 1,6 D-glucan derived from Ganoderma lucidum in healthy adult volunteers, a randomized controlled trial. Foods. 2023;12(3):659. PMID 36766186
- Wicks SM, Tong R, Wang CZ, et al. Safety and tolerability of Ganoderma lucidum in healthy subjects: a double-blind randomized placebo-controlled trial. American Journal of Chinese Medicine. 2007;35(3):407–414. PMID 17597499
- Tao J, Feng KY. Experimental and clinical studies on inhibitory effect of ganoderma lucidum on platelet aggregation. Journal of Tongji Medical University. 1990;10(4):240–243. PMID 2098581
- Wanmuang H, Leopairut J, Kositchaiwat C, Wananukul W, Bunyaratvej S. Fatal fulminant hepatitis associated with Ganoderma lucidum (Lingzhi) mushroom powder. Journal of the Medical Association of Thailand. 2007;90(1):179–181. PMID 17621752
- Guedikian R, Kim B, Singh G, Alexander R. Ganoderma lingzhi (reishi mushroom)-induced acute liver injury in the setting of alcohol use: a case report and review of the literature. Cureus. 2023;15(9):e45953. PMID 37885515
Read more on the blog
- Reishi (Ganoderma lucidum): The Mushroom of Immortality →
- Medicinal Mushrooms: How Fungi Support Your Immune System →
- Type 2 Diabetes: Early Signs, Risks and Prevention →
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The team at SANUSq.
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