Beta-glucans are long sugar chains, called polysaccharides, found in the cell walls of mushrooms, yeast, oats, and barley. In mushrooms, they are a main structural fiber in the cell wall, and research shows they can bind to receptors on immune cells and influence how those cells respond to threats. That immune-signaling role is why mushroom beta-glucans have been studied for decades, mostly as an add-on to standard medical treatment rather than as a stand-alone cure.
A Safety Note Before You Read Further
Beta-glucans work by activating parts of the immune system. That is exactly why people on immune-suppressing medicine need to be careful with them. If you take medicine after an organ transplant, have an autoimmune condition such as lupus or rheumatoid arthritis, or are scheduled for surgery, talk with your prescribing clinician before adding a mushroom beta-glucan supplement. Reishi mushroom, one of the most common beta-glucan sources in supplements, can also increase bleeding risk and may need to be stopped roughly two weeks before a scheduled surgery. There is not enough reliable evidence to know whether reishi is safe during pregnancy or breastfeeding, so many clinicians recommend avoiding it in that situation. See our safety and interactions overview for more on how we handle these cautions across the site.
The Structure of a Beta-Glucan
A beta-glucan is built from repeating glucose units connected by chemical bonds called beta-glycosidic linkages. The exact pattern of those linkages, and how many side branches hang off the main chain, changes what the molecule does in the body and how it is classified. This pattern is not identical across every mushroom or every extract. It varies by species, by which compound within the mushroom is being studied, and by how the product was made.
- Backbone type: many fungal beta-glucans have a 1,3-linked backbone, though some studied mushroom polysaccharides show other linkage patterns, including mixed 1,3 and 1,4 links.
- Branching: side branches, often 1,6-linked, are common in fungal beta-glucans and affect how the immune system recognizes the molecule.
- Molecular weight: mushroom beta-glucans are typically large, high-molecular-weight molecules, which affects how well they dissolve and how the body processes them.
How Mushroom Beta-Glucans Differ From Grain Beta-Glucans
Not all beta-glucans are the same, even though they share a name. Oat and barley beta-glucans have a well-defined, mostly straight backbone that is chemically distinct from the more varied, often branched structures found in mushrooms and fungi.
- Oat and barley beta-glucans have a mixed 1,3 and 1,4-linked backbone that is largely unbranched. This is the form the FDA recognized in 1997 for a heart-health claim: soluble fiber such as oat beta-glucan, eaten as part of a diet low in saturated fat and cholesterol, may help reduce the risk of heart disease at intakes of at least 3 grams a day.
- Mushroom beta-glucans tend to be more branched and are the polysaccharides most closely tied to the immune-signaling research described below. Even within mushrooms, the structure is not uniform: for example, the purified turkey tail compound PSK has a 1,4-linked backbone with 1,3 and 1,6-linked side branches, a different pattern than some other mushroom polysaccharides.
In plain terms: a cereal beta-glucan and a mushroom beta-glucan are related molecules studied for different purposes. Evidence for one should not be assumed to apply to the other.
How Beta-Glucans Are Thought to Modulate Immunity
Immune cells such as macrophages and natural killer cells carry receptors on their surface, including one called complement receptor 3, that can recognize and bind beta-glucan molecules. Research suggests this binding can trigger a chain of signals that activates parts of the innate immune system, the body’s first line of defense against germs and abnormal cells.
A 2024 laboratory study from Trinity College Dublin found that beta-glucans extracted from the common button mushroom (Agaricus bisporus) could “train” immune cells in a dish to respond more strongly to a later challenge, a process researchers call trained immunity. This is preclinical, cell-based research, not a study in people, so it shows a plausible mechanism rather than a proven human health benefit.
What Human Clinical Evidence Actually Shows
The strongest human evidence for mushroom beta-glucans does not come from over-the-counter supplements. It comes from a purified, pharmaceutical-grade turkey tail (Trametes versicolor) extract called PSK, used as a prescription add-on to chemotherapy in Japan since the mid-1970s.
- Gastric cancer: A meta-analysis of eight randomized trials covering 8,009 patients found that adding PSK to standard chemotherapy after curative surgery was linked to improved overall survival compared with chemotherapy alone.
- Colorectal cancer: A separate meta-analysis of three randomized trials covering 1,094 patients found better 5-year disease-free and overall survival in the PSK group compared with chemotherapy alone.
- Lung cancer: A systematic review of six randomized controlled trials found that adding PSK to chemotherapy or radiation improved at least one outcome, such as immune measures, body weight, or survival, in every study reviewed.
These trials tested PSK as a medically supervised adjunct to chemotherapy in people already being treated for cancer, not as a general wellness supplement taken on its own. That distinction matters: it means this evidence does not establish that an over-the-counter turkey tail or beta-glucan capsule will produce the same effect in a healthy person hoping to avoid a cold.
Reishi: A Different Chemistry Story
Reishi (Ganoderma lucidum) is often marketed alongside turkey tail as a beta-glucan source, but much of the laboratory research on reishi’s anticancer activity points to a different class of compounds called triterpenoids, alongside its polysaccharides. According to the National Cancer Institute’s clinician-facing review, there are no human studies that have measured cancer outcomes for reishi, only mechanistic studies looking at immune markers in blood samples and a colorectal-adenoma prevention study using a water-soluble mycelium extract. Reishi products can also vary widely in what they actually contain, since triterpenes and polysaccharides are pulled out by different extraction methods.
Why Extraction Method Changes What You Actually Get
Two supplements labeled with the same mushroom species can contain very different amounts of active beta-glucan, depending on how they were made.
- Hot-water extraction pulls polysaccharides, including beta-glucans, out of the mushroom material and is the traditional method used to make products like PSK.
- Alcohol extraction is better suited to pulling out compounds like triterpenes, and generally yields less beta-glucan.
- Fruiting body versus mycelium-on-grain: research on Ganoderma products notes that mycelium grown on a grain substrate such as rice can retain starch-derived alpha-glucans from that grain, while fruiting-body extracts are entirely beta-glucan in nature. Standard lab tests do not always separate alpha-glucans from beta-glucans, so a product can report a high polysaccharide number that is partly leftover grain starch rather than mushroom beta-glucan.
- Manufacturing consistency: dietary supplements are not required to undergo premarket safety and effectiveness review before they reach store shelves, and while manufacturers must follow good manufacturing practice rules, testing has found that ingredient amounts can still vary from the label and from batch to batch.
This is one reason our evidence grading system ties a grade to a specific extraction method and dose, not to a mushroom species in general.
Evidence Snapshot
- Purified turkey tail extract (PSK) plus chemotherapy, gastric and colorectal cancer: multiple randomized trials and meta-analyses in adults undergoing cancer treatment; grade B, moderate human evidence, with limitations including older trial designs and use only in Japan under medical supervision.
- Reishi fruiting body or spore extracts, general immune markers: small mechanistic human studies plus laboratory and animal research; grade D, preclinical or traditional basis, since there are no human studies measuring actual health outcomes.
- Over-the-counter mushroom beta-glucan capsules, general cold or immune “support” in healthy adults: grade E, insufficient direct evidence, because the human trials above tested a different product, population, and purpose than most retail supplements.
Who Should Use Extra Caution
- People taking immunosuppressive medication, including organ transplant recipients.
- People with an autoimmune condition such as lupus, rheumatoid arthritis, or multiple sclerosis.
- People scheduled for surgery in the next two weeks, due to a possible increased bleeding risk with reishi.
- People who are pregnant or breastfeeding, since reliable safety data is lacking.
- People taking blood thinners, blood pressure medicine, or diabetes medicine, since reishi may affect blood clotting, blood pressure, and blood sugar.
Frequently Asked Questions
Are mushroom beta-glucans the same as the beta-glucans in oats?
No. They share a name and a general sugar-chain structure, but the chemical linkage pattern is different. Oat and barley beta-glucans have a largely unbranched structure tied to cholesterol-lowering effects. Mushroom beta-glucans tend to be more branched and are studied mainly for immune signaling. Evidence for one does not transfer to the other.
Does eating mushrooms give me the same beta-glucans as a supplement?
Whole mushrooms do contain beta-glucans in their cell walls, but raw or lightly cooked mushrooms have tough chitin-based cell walls that are difficult for the body to break down. Most of the human research described here used concentrated hot-water extracts, not mushrooms eaten as food, so the dose and form are not directly comparable.
Can a mushroom beta-glucan supplement help me avoid getting sick?
There is no reliable human evidence that over-the-counter mushroom beta-glucan supplements prevent colds or other infections in generally healthy people. The strongest human data involves a purified pharmaceutical extract used alongside cancer treatment under medical supervision, which is a different use case entirely.
Are mushroom beta-glucan supplements safe to take with my medication?
Possibly not, depending on the medication. Because beta-glucans can stimulate immune activity, they may work against immunosuppressive drugs. Reishi specifically can interact with blood thinners, blood pressure medicine, and diabetes medicine. Tell your doctor or pharmacist about any mushroom supplement you take so they can check it against your medication list.
This article is for general education and is not medical advice. It does not diagnose any condition or recommend that you start, stop, or change a medication or supplement. Evidence for mushroom compounds varies by species, extraction method, dose, and the population studied, and much of the strongest human evidence involves purified pharmaceutical extracts used under medical supervision rather than retail supplements. Talk with a qualified clinician about your own health history, medications, and any interest in mushroom-based products. Learn more about how our team reviews and updates this kind of content in our editorial team and review process.