Mushrooms and Natural Killer Cell Activity: Research Review

Mushrooms & Innate Immunity

58% of cancer patients improved

Fifty-eight percent of cancer patients showed measurable NK cell improvement after Maitake D-Fraction supplementation, setting off a decade of research across athletes, healthy adults, and the elderly.

Kodama et al., J Med Food, 2003

5 RCTs

with direct NK cell outcomes across different populations

p<0.002

NK cell improvement in a 100-patient chemotherapy trial (Ahn, 2004)

4 weeks

of dietary shiitake improved NK cell activity in healthy adults (Dai, 2015)

Kodama et al., J Med Food, 2003

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NK cells, natural killer cells, are the immune system's fast-response killers. They patrol for cells that look wrong: tumor cells, virus-infected cells, any cell that has stopped displaying the normal surface markers that say "I'm healthy." They destroy those cells on contact without waiting for instruction from the adaptive immune system, which can take days to mobilize.

The research on mushrooms and natural killer cell activity now spans five randomized controlled trials, several cohort studies, and a body of lab and animal work. The short version: yes, the effect is real across multiple mushroom species and multiple populations. The longer version is more interesting, because what the effect means differs substantially depending on whether the subjects were cancer patients, competitive athletes, or healthy adults. For the complete picture of mushroom beta-glucan immune research, see the guide to mushroom beta-glucans and immunity.

What NK Cells Do, and Why Measuring Them Is Complicated

Natural killer cells are part of the innate immune system. Unlike T cells, which must be specifically trained to recognize a particular pathogen, NK cells respond based on general patterns, particularly the absence of "healthy cell" surface markers. This lets them act within hours rather than days.

Measuring NK cell function in research is harder than it sounds. The standard assay mixes a subject's NK cells with tumor cells in a lab dish and measures what percentage of those tumor cells are killed over a fixed time window. Different labs use different tumor cell lines, different ratios of NK cells to targets, and different time points. A "50% increase in NK cell activity" in one trial may use parameters that would register as 20% using another lab's protocol.

This measurement inconsistency is worth holding in mind as you read through the clinical trials below. The directional consistency across studies matters more than any single percentage number.

The Preclinical Foundation: Lab Studies and Animal Evidence

Before the human trials, researchers established biological plausibility in lab conditions and animal models.

In 2005, Kodama's team showed that maitake D-Fraction, a purified polysaccharide fraction extracted from Grifola frondosa, enhanced NK cell killing capacity against tumor cells in a dose-dependent pattern.^[3] Higher concentrations produced greater cytotoxicity (the technical term for cell-killing ability) in a linear relationship. This was lab-dish work, but it showed that D-Fraction had direct effects on how aggressively NK cells attacked their targets.

White button mushrooms, the most commonly consumed species worldwide, also showed the effect in an animal model. Wu's 2007 study found that dietary supplementation with Agaricus bisporus enhanced NK cell activity in mice, alongside increases in interferon-gamma and TNF-alpha.^[4] Interferon-gamma is a signaling protein that macrophages release when activated; it's one of the main signals that then turns on NK cells. The fact that both went up together hints at the indirect activation mechanism that later research confirmed.

Vetvicka and Vetvickova ran one of the few direct species comparisons, testing maitake and shiitake extracts side by side in the same animal model. Both enhanced NK cell activity and macrophage phagocytosis (the process by which immune cells engulf and destroy threats) above the untreated control group. Maitake showed slightly higher NK cell enhancement than shiitake.^[11] Animal comparisons don't map directly to species rankings in humans, especially across different extraction methods and doses, but they established that species-level differences in NK cell effect were real and measurable.

Five Clinical Trials with NK Cell Outcomes

The human evidence is built around five randomized trials spanning three very different populations:

The direction of effect is consistent across all five. The magnitude and clinical meaning are not, and that difference is the most important thing the table doesn't show.

Cancer Patients: The Strongest Signal, the Hardest to Generalize

Kodama studied 35 cancer patients given Maitake D-Fraction supplementation.^[1] By the end of the study, 58% showed measurable improvement in NK cell activity. This was a cohort study without a randomized control group, so it can't rule out placebo effects or confounding variables. But it was the study that launched serious clinical interest in mushrooms and NK cell function and set the reference point that subsequent trials aimed to confirm.

Ahn's 2004 trial is the strongest piece of human evidence in this area. His team randomized 100 gynecological cancer patients undergoing chemotherapy to either Agaricus blazei Murill Kyowa extract or placebo.^[2] The extract group showed significantly higher NK cell activity (p<0.002) and also reported higher quality-of-life scores compared to the placebo group. This was a prospective randomized design, 100 participants, highly statistically significant.

The caveat is important to state directly. Chemotherapy is known to suppress NK cell activity as a side effect. These patients started from an abnormally suppressed baseline. The intervention helped them recover toward normal, which is genuinely meaningful for that population, but it's a distinct clinical question from whether the same compound can push NK cells beyond their normal range in healthy people. The cancer data doesn't answer the healthy-adult question.

Athletes Under Stress: Protecting What You Have

The athlete data is built around a well-documented immune phenomenon. After intense training, NK cell activity drops for 3-72 hours in what researchers sometimes call the "open window" of post-exercise immune vulnerability. During this period, athletes are measurably more susceptible to upper respiratory infections.

Pleuran, a specific beta-glucan fraction extracted from Pleurotus ostreatus (the oyster mushroom), was studied in this context. Bobovčák assigned 50 elite athletes to pleuran supplementation or placebo and measured NK cell activity after intensive exercise.^[5] The supplemented group maintained NK cell activity where the placebo group showed the expected post-exercise drop.

Bergendiova extended this to a 3-month randomized trial with 50 athletes.^[6] Pleuran supplementation significantly improved NK cell activity and, critically, reduced the incidence of upper respiratory infections over the study period. That connection between an immune marker (NK cell activity) and a practical outcome (fewer sick days) is something most immune studies don't achieve, and it makes Bergendiova 2011 one of the more clinically meaningful papers in this area.

Majtan's 2012 systematic review of pleuran trials concluded that the NK cell improvements and reduced infection incidence were consistent findings across the studies reviewed.^[8] For how polysaccharides from oyster and other mushrooms interact with a different immune cell type, see Mushroom Polysaccharides and Neutrophil Enhancement.

Healthy Adults: Where the Evidence Is Thinner but Most Relevant

Studies in people without any immune stress are the hardest test. They're also the most relevant to the largest number of people reading this.

Dai's 2015 randomized trial enrolled 52 healthy adults and assigned them to eat 5-10 grams of dried shiitake mushrooms daily for 4 weeks or to receive no mushrooms.^[12] The mushroom group showed improvements in immune cell proliferation, NK cell activity, secretory IgA (a mucosal immune protein that protects respiratory tissue), and lower C-reactive protein, a blood marker that rises when inflammation is present. This is a practically significant study: the intervention was dietary food, not a supplement, at amounts that represent a realistic daily serving available at any grocery store.

Kang randomized 79 healthy Korean men to Cordyceps militaris supplementation or placebo. The Cordyceps group showed enhanced cell-mediated immunity, the branch of immune function that includes NK cells and T cells, versus the placebo group.^[13] A comprehensive 2026 review of Cordyceps militaris immune research by Yang and colleagues identifies NK cell enhancement as one of the consistent findings across multiple studies.^[14] For more on Cordyceps-specific immune mechanisms, see Cordyceps militaris Polysaccharides and Immune Activation.

Gaullier studied healthy elderly adults in a crossover design, meaning each participant spent time in both the supplement and placebo conditions and served as their own control.^[7] Participants showed better NK cell activity during the shiitake mycelium soluble beta-glucan supplementation period than during the placebo period.

The honest characterization of the healthy-adult evidence: real effects, multiple species, but smaller than what's seen in cancer patients or exercise-stressed athletes. Enhancing immune function that's already operating in its normal range is a harder task than recovering function that's been suppressed.

How Mushrooms Actually Activate NK Cells: The Indirect Route

Here is the part of mushroom immunology that most popular coverage gets wrong.

NK cells don't express Dectin-1, the main surface receptor on macrophages that recognizes mushroom beta-glucans. So when you eat or supplement with mushroom beta-glucans, those polysaccharides cannot activate NK cells by binding to them directly. There's no physical connection between the beta-glucan and the NK cell.

The mechanism runs through other immune cells. Beta-glucans bind Dectin-1 on macrophages and dendritic cells (immune cells that act as messengers between the innate and adaptive systems), triggering those cells to produce a set of signaling proteins. Three of those proteins, IL-12, IL-15, and IL-18, are the actual molecular signals that activate NK cells. The mushroom talks to the macrophage. The macrophage talks to the NK cell. The NK cell then activates.

This indirect pathway also explains the Wu 2007 mouse findings: white button mushroom supplementation elevated interferon-gamma and TNF-alpha alongside the NK cell activity increases.^[4] Both are signature outputs of macrophage activation that appear in the signaling chain before the NK cell response.

For a detailed look at how the macrophage activation step works, see How Medicinal Mushrooms Activate Macrophages. For evidence that repeated beta-glucan exposure can create lasting changes in macrophage behavior, a phenomenon called trained immunity, see Mushrooms and Innate Immunity: How They Prime Your First Line of Defense.

Mushrooms also activate immune cells through mechanisms that don't involve beta-glucans at all. Tsao isolated a novel protein from maitake that activated both NK cells and dendritic cells in mice, producing antitumor immune effects that were independent of D-Fraction polysaccharide.^[10] This protein-based activation pathway hasn't been studied in humans, but it suggests that whole mushroom consumption may involve multiple active compounds hitting multiple immune targets simultaneously.

Turkey Tail mushroom's PSK, a polysaccharide isolate, activated gamma-delta T cells in lab conditions.^[9] Gamma-delta T cells are innate immune cells that patrol for stress signals and kill abnormal cells in a pattern functionally similar to NK cells. Clinical trials that measure "NK cell activity" rarely specify whether they're capturing true NK cell effects, gamma-delta T cell contributions, or both. That ambiguity is a genuine gap in measurement precision across the field.

For a broader picture of how mushrooms affect all three innate immune cell types together, see Mushrooms and Innate Immunity: How Fungi Prime Your First Line of Defense. For evidence that beta-glucan exposure can create lasting immune memory, see Beta-Glucans and Innate Immune Memory: Beyond Adaptive Immunity.

What These Studies Can't Tell You

NK cell activity assays are surrogate markers, not disease outcomes. Higher NK cell cytotoxicity in a lab measurement correlates with better immune surveillance capacity, but clinical relevance requires connecting that marker to actual infection or disease outcomes. Of the five randomized trials discussed here, Bergendiova 2011 is the only one to make that connection explicitly, and it's in a single population (athletes) with one outcome (upper respiratory infections).

Most of the dramatic results came from immune-suppressed populations. Cancer patients on chemotherapy and elite athletes during heavy training both start from depressed baselines. The same intervention that helps suppressed NK cells recover toward normal may produce much smaller effects in people whose NK cells are already operating within their normal functional range.

Form incompatibility across studies prevents meaningful species ranking. Maitake D-Fraction is a purified polysaccharide produced by a specific extraction process. Pleuran is a distinct beta-glucan fraction from oyster mushrooms. Dietary dried shiitake is a whole food. Shiitake mycelium extract is a different form of the same species as dried shiitake. Cordyceps militaris in the Kang trial was a standardized supplemental preparation. These forms differ in polysaccharide concentration, bioavailability, and accompanying compounds. No trial has compared them head-to-head in the same population.

The clearest practical signal from the human evidence: dietary shiitake at 5-10g daily for 4 weeks (Dai 2015) and Cordyceps militaris supplementation (Kang 2015) both produced NK cell improvements in randomized trials in healthy adults with no immune challenges. The shiitake finding is particularly notable because it used a food amount rather than a supplement dose.

The Bottom Line

Multiple randomized trials across cancer patients, athletes, and healthy adults show that different mushroom species can enhance NK cell activity. Effects are most dramatic in immune-suppressed populations and more modest, but present, in healthy individuals. The mechanism is indirect: beta-glucans activate macrophages, which then produce the signaling proteins that turn on NK cells. Multiple non-beta-glucan mushroom compounds also appear to contribute. Form, dose, and population context determine what the data actually shows for any given study.

Frequently Asked Questions

Which mushroom boosts natural killer cell activity?

Multiple species have clinical evidence: maitake D-Fraction improved NK cell activity in 58% of cancer patients (Kodama 2003), Agaricus blazei extract produced a significant NK cell increase in a 100-patient randomized trial (Ahn 2004), pleuran from oyster mushrooms maintained NK activity in athletes during post-exercise immune suppression (Bergendiova 2011), Cordyceps militaris enhanced NK cell function in 79 healthy men (Kang 2015), and dietary shiitake improved NK cell activity in healthy adults eating 5-10g daily for 4 weeks (Dai 2015). The data don't support ranking these species because the trials used different populations, forms, and doses.

Do medicinal mushrooms increase NK cells in humans?

Yes. Five randomized controlled trials have measured NK cell improvements after mushroom supplementation in humans, across populations ranging from cancer patients undergoing chemotherapy to healthy adults eating dried shiitake. The directional effect is consistent across studies, though it is stronger in immune-suppressed populations than in healthy baselines.

How do mushrooms help natural killer cells fight cancer?

The clearest clinical data comes from Ahn's 2004 randomized trial in which 100 cancer patients on chemotherapy received Agaricus blazei extract and showed significantly better NK cell activity than the placebo group (p<0.002). The mechanism runs indirectly through macrophages: mushroom beta-glucans activate macrophages, which then release IL-12, IL-15, and IL-18, the signaling proteins that turn on NK cells. The effect in cancer patients is partly about recovering NK function suppressed by chemotherapy.

What is the best supplement to boost NK cells naturally?

The strongest randomized trial evidence in healthy populations points to Cordyceps militaris (Kang 2015, n=79 healthy men) and dietary shiitake at 5-10g daily (Dai 2015, n=52 healthy adults). For athletes specifically, pleuran from oyster mushrooms has two randomized trials supporting NK cell maintenance during intense training (Bobovčák 2010, Bergendiova 2011). No trial compares these head-to-head in the same population, so a definitive ranking isn't supported by current evidence.

Can Agaricus blazei increase NK cell activity in cancer patients?

Yes. Ahn's 2004 randomized trial, the largest mushroom-specific NK cell trial in cancer patients, found that Agaricus blazei Murill Kyowa extract significantly improved NK cell activity (p<0.002) in 100 gynecological cancer patients undergoing chemotherapy, compared to placebo. Quality-of-life scores also improved in the supplemented group. The population was immune-suppressed from chemotherapy, which is important context for interpreting the effect size.

How long does it take for mushrooms to affect NK cell activity?

The trials that measured at defined time points found effects within weeks. Dai's 2015 dietary shiitake trial measured improvements at the 4-week mark. Bergendiova's pleuran trial ran 3 months and showed consistent improvement across that period. The Ahn cancer trial and Kang Cordyceps trial used multi-week supplementation windows. No trial has specifically tested the minimum duration needed to produce an effect.

Sources & References

1. 1RTHM-00112·Kodama, Noriko et al. (2003). “Effect of Maitake (Grifola frondosa) D-Fraction on the activation of NK cells in cancer patients..” Journal of medicinal food.Study breakdown →PubMed →↩
2. 2RTHM-00066·Ahn, W-S et al. (2004). “Natural killer cell activity and quality of life were improved by consumption of a mushroom extract, Agaricus blazei Murill Kyowa, in gynecological cancer patients undergoing chemotherapy..” International journal of gynecological cancer : official journal of the International Gynecological Cancer Society.Study breakdown →PubMed →↩
3. 3RTHM-00162·Kodama, Noriko et al. (2005). “Enhancement of cytotoxicity of NK cells by D-Fraction, a polysaccharide from Grifola frondosa..” Oncology reports.Study breakdown →PubMed →↩
4. 4RTHM-00236·Wu, Dayong et al. (2007). “Dietary supplementation with white button mushroom enhances natural killer cell activity in C57BL/6 mice..” The Journal of nutrition.Study breakdown →PubMed →↩
5. 5RTHM-00327·Bobovčák, Marián et al. (2010). “Effect of Pleuran (β-glucan from Pleurotus ostreatus) supplementation on cellular immune response after intensive exercise in elite athletes..” Applied physiology.Study breakdown →PubMed →↩
6. 6RTHM-00379·Bergendiova, Katarina et al. (2011). “Pleuran (β-glucan from Pleurotus ostreatus) supplementation, cellular immune response and respiratory tract infections in athletes..” European journal of applied physiology.Study breakdown →PubMed →↩
7. 7RTHM-00394·Gaullier, Jean-Michel et al. (2011). “Supplementation with a soluble β-glucan exported from Shiitake medicinal mushroom, Lentinus edodes (Berk.) singer mycelium: a crossover, placebo-controlled study in healthy elderly..” International journal of medicinal mushrooms.Study breakdown →PubMed →↩
8. 8RTHM-00476·Majtan, Juraj (2012). “Pleuran (β-glucan from Pleurotus ostreatus ): an effective nutritional supplement against upper respiratory tract infections?.” Medicine and sport science.Study breakdown →PubMed →↩
9. 9RTHM-00291·Inatsuka, Carol et al. (2013). “Gamma delta T cells are activated by polysaccharide K (PSK) and contribute to the anti-tumor effect of PSK..” Cancer immunology.Study breakdown →PubMed →↩
10. 10RTHM-00558·Tsao, Yao-Wei et al. (2013). “Characterization of a novel maitake (Grifola frondosa) protein that activates natural killer and dendritic cells and enhances antitumor immunity in mice..” Journal of agricultural and food chemistry.Study breakdown →PubMed →↩
11. 11RTHM-00654·Vetvicka, Vaclav et al. (2014). “Immune-enhancing effects of Maitake (Grifola frondosa) and Shiitake (Lentinula edodes) extracts..” Annals of translational medicine.Study breakdown →PubMed →↩
12. 12RTHM-00368·Dai, Xiaoshuang et al. (2015). “Consuming Lentinula edodes (Shiitake) Mushrooms Daily Improves Human Immunity: A Randomized Dietary Intervention in Healthy Young Adults..” Journal of the American College of Nutrition.Study breakdown →PubMed →↩
13. 13RTHM-00378·Kang, Ho Joon et al. (2015). “Cordyceps militaris Enhances Cell-Mediated Immunity in Healthy Korean Men..” Journal of medicinal food.Study breakdown →PubMed →↩
14. 14RTHM-02247·Yang, Eun-Ju et al. (2026). “An Immunomodulatory Mushroom, Cordyceps militaris, and Its Constituents: A Review of In Vitro/In Vivo Studies and Clinical Trials..” Phytotherapy research : PTR.Study breakdown →PubMed →↩