Lentinula edodes, or shiitake mushroom, has been cultivated for centuries as a medicinal agent. A study conducted at the University of Florida and published in the Journal of the American College of Nutrition set out to determine the relationship between consumption of L. edodes mushroom and human immune function. More specifically, the research team wanted to ascertain whether consuming L. edodes would improve markers of immune response, especially γδ-T cell proliferation and activation. γδ-T cells are T lymphocytes that behave more like cells of the innate immune system as they do not require the major histocompatibility complex for processes. They are located in the epithelium of the gut, lungs and genitourinary tract. The researchers were also interested in possible changes in natural killer T (NK-T) cell proliferation and activation and levels of secretory immunoglobulin A (sIgA) in saliva and C-reactive protein (CRP) in serum.
To tease out the immunomodulatory effects of the shiitake mushroom, volunteers were recruited according to a strict list of exclusions. Vegans and vegetarians were excluded, as were people who regularly drank tea or took antioxidant or probiotic supplements. Also excluded were people who consumed more than 14 glasses of alcoholic beverages per week or ate more than 7 servings of fruits and vegetables per day. These restrictions were necessary because many of these substances could boost or suppress the immune system and thereby modify the effects of shiitake consumption.
Ultimately, 52 healthy participants (20 men, 32 women) between the ages of 21 and 41 years participated in the parallel group study. Researchers gave each participant a 4-week supply of dried shiitake mushrooms with instructions on how to rehydrate and cook them; participants were then randomly assigned to consume packets of either 5 g or 10 g of L. edodes daily. Blood, saliva, and serum samples were collected at baseline and after daily L. edodes consumption at 4 weeks.
Over the course of the study, all participants blood work showed improving function in γδ-T cells (60% greater, P<0.0001) and NK-T cells (2-fold greater, P<0.0001), and both cell types demonstrated a greater ability to express activation receptors. Likewise, sIgA levels increased, which signaled improved gut immunity, and a 30% reduction in CRP levels suggested less inflammation. While both doses were effective, higher dose of 10g daily yielded more significant changes.
The authors concluded that regular consumption of shiitake mushrooms may result in improved immunity and decreased inflammation. Although larger trials are warranted, these preliminary findings hold promise for immunocompromised patients seeking natural therapies.
Dai X, Stanilka JM, Rowe CA, et al. Consuming Lentinula edodes (shiitake) mushrooms daily improves human immunity: a randomized dietary intervention in healthy young adults. J Am Coll Nutr. 2015 Apr 11:1-10. [Epub ahead of print]

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