Maitake mushroom (Grifola frondosa) is a medicinal and culinary mushroom. In Japanese, “maitake” means “dancing mushroom”^[2], possibly because people danced joyfully when they first discovered it, although the name may simply be due to its unique appearance. During Japan’s feudal era, maitake held such value that it was used as a form of currency, worth its weight in silver.^[3] Maitake is still considered an elite culinary mushroom in Japan.^[4]

Maitake mushrooms are commonly found in North America and Asia; while they are also present in Europe, they are less common there.^[4] These mushrooms typically grow in clusters at the base of trees with broad leaves, such as oaks, but are also found on chestnut, elm, and maple trees.^[5]

Maitake showed promising anti-tumor and immunomodulatory properties in numerous preclinical trials.^[6][6] However, it’s important to exercise caution when interpreting these results, because animal models of human disease often have significant specificity to that animal, due to biological and immunological differences from humans. Moreover, clinical (human) research on maitake’s effects on humans remains limited.

In one phase 1–2 clinical trial involving postmenopausal women with a history of (but no current) breast cancer, maitake extract was given orally at gradually increasing dosages over three weeks. The results showed that maitake increased the production of both stimulatory and suppressive cytokines, which play a key role in the regulation of the immune system response.^[1] Although these findings did not lead to any observable clinical changes, they did suggest that maitake has complex effects on the immune system. Although some people may benefit from it, individuals with cancer should consider maitake supplementation carefully due to its immunosuppressive effects.

Another small non-randomized clinical trial assessed the levels of immunomodulatory markers in individuals with stage II–IV lung, lingual, gastric, and breast cancer who were given maitake’s D-fraction (a bioactive extract; see below under “How does maitake work?”) twice daily at different dosages based on the specific type of cancer. The study found slightly increased levels of T cells ( CD4+ and CD8+) and enhanced natural killer (NK) cell activity following treatment. Although these results suggest that matiake’s D-fraction may have immunostimulatory properties and a potential inhibitory effect on cancer progression, it’s important to note that the outcomes varied among different cancer groups. Additionally, two patients died despite the observed increase in T cells.^[7] Given the study design and size, these findings should be interpreted with caution.

Finally, one non-controlled clinical trial reported mixed results for the effect of maitake on HIV infection. T cell (specifically CD4+ cells) activity and viral load improved for some participants, but worsened for others.^[8] More clinical studies should be conducted to explore efficacy and safety of maitake supplementation for people with HIV.

Only a few clinical studies have assessed adverse events associated with maitake supplementation.

In one phase 1–2 clinical trial involving menopausal women with resected breast cancer, no severe side effects were reported. However, two of the 34 participants dropped out of the study due to adverse reactions. One participant experienced symptoms of nausea and joint pain (at a dosage of 1mg/kg per day), while another participant had an allergic reaction to the supplement (at a dosage of 10mg/kg per day).^[1]

Finally, in one study, levels of the immunosuppressive cytokine IL-10 was increased after maitake supplementation^[1], suggesting that it may not be suitable for individuals with cancer or a compromised immune system.

Most studies on maitake have utilized a bioactive extract known as the D-fraction. The D-fraction is typically extracted from the mushroom’s fruiting body and is composed of a proteoglucan, which is a beta-glucan and protein complex in a ratio ranging from 80:20–99:1.^[2][1] It appears that maitake’s D-fraction exerts its antitumor effects by inducing apoptosis in, and autophagy of, cancerous cells.^[6]

Moreover, preclinical^[6] and clinical^[7][1] studies have demonstrated that maitake’s D-fraction works by modulating the immune system. Preclinical studies have observed that maitake increases the activation of T cells, specifically CD4+ and CD8+ T cells, and enhances the secretion of immunostimulatory cytokines (i.e., IL-2, IL-12, TNF-α, and IFN-γ)^[6] Clinical trials involving individuals with cancer have confirmed these findings, demonstrating increased levels of stimulatory cytokines (e.g, IL-2)^[1], enhanced T cell activation, and increased NK cell activity^[7]. Additionally, one study noted an increase in levels of interleukin 10 (IL-10), which at least partially explains maitake’s potential immunosuppressive mechanism.^[1]