Originally hailing from Asia, shiitake mushrooms (Lentinula edodes or Lentinus edodes) have been used for centuries both as a food and for their medicinal qualities. L. edodes has been shown in research to support many functions in human health, including lipid and glucose metabolism, normal blood pressure, antioxidant activity, and healthy cellular functioning. This species has also been shown to have antimicrobial and antiviral properties in vitro, and it may also possess immunomodulating properties and potential activity against some types of cancer cells.

Shiitake mushrooms have been thoroughly researched for their potential effects on the immune system. A 4-week randomized control trial studied the effects of supplementation with L. edodes on inflammatory markers in healthy individuals. The study found a significant reduction of C-reactive protein (CRP) in the participants consuming mushrooms, along with an increase in interleukin (IL)-4 and IL-10, two of the markers associated with an anti-inflammatory response due to their role in the downregulation of inflammatory cytokines. Lentinan is a beta-glucan constituent in L. edodes that is linked to interaction with the human immune system. It has been shown to interact with toll-like receptors on macrophages, dendritic cells, and other immune cells. It is also believed that beta-glucans are fermented by microbes in the large intestine, and this study showed an increase in immunoglobulin A levels after consuming L. edodes, which suggests a beneficial effect on mucosal immunity.

Another study explored the effects of supplementation with the probiotic Bifidobacterium longum (Bifidus BB536) combined with L. edodes after antibiotic use. This double-blind study had four treatment arms: a placebo, B. longum, L. edodes, and the combination of B. longum and L. edodes. The study findings suggest that combining B. longum and L. edodes may modulate dendritic cell subgroup production and activity, which could have further implications regarding the potential benefits of combining probiotics with shiitake mushrooms after administering antibiotics.

Shiitake mushrooms have also been a subject of study regarding their possible direct effects on the microbiome. Recent animal studies have suggested that long-term supplementation with beta-glucans from L. edodes could attenuate gut microbial dysbiosis that is associated with a chronic high-fat diet. The researchers in this study also explored the potential of L. edodes to support the prevention of cognitive decline associated with a chronic high-fat diet. Current research postulates that intestinal barrier impairment from causes, such as a chronic high-fat diet can mediate neuro-inflammation and microglial activation through the gut–brain axis. This study noted the effects of L. edodes on these downstream consequences of the chronic high-fat diet. Although a typical chronic high-fat diet may increase microglial numbers in the hippocampal regions, this study reported that supplementation with beta-glucans from L. edodes significantly reduced the microglial number. In addition, downregulation of pro-inflammatory cytokines and improvements in memory were noted in the treatment arm.

Shiitake mushrooms support human health in a wide variety of functions, and recent research has suggested the exciting new possible ways that L. edodes could have an effect on the gastrointestinal microbiome and the gut–brain axis. There are likely even more roles that future research will find for the mighty shiitake mushroom.

By Colleen Ambrose, ND, MAT