In the June 25 issue of The ASCO Post, the Integrative Oncology column by Ting Bao, MD, DABMA, MS, and Jyothirmai Gubili, MS, focused on how to counsel a patient about shiitake mushroom. They concluded: “We advised our patient that it is safe to take shiitake mushroom to boost her immune system.” Unfortunately, the evidence the authors supply—a single human study—is insufficient to support this statement.
In this study,1 52 healthy volunteers underwent blood draws and were randomized to eating 5 or 10 g of dried shiitake mushroom. They were asked to stop the “consumption of tea, flavonoid-containing supplements, antioxidant supplements, or probiotics.” They were also instructed “not to consume more than 14 glasses of alcoholic beverages per week or more than 7 servings of fruits and vegetables per day.” A number of immune measurements were taken and compared within the group, from baseline to the end of the intervention.
Comparisons against baseline are inappropriate for randomized trials,2 and in this case, they are particularly problematic, as the intervention is confounded by numerous concurrent recommendations. The results of this trial are essentially meaningless.
Therefore, in the absence of credible evidence, it is inappropriate to confirm the patient’s belief. Instead the authors should counsel the patient that she can eat shiitake mushroom if she wishes, but they are unaware of any credible evidence it will boost the immune system. ■
—Vinay Prasad, MD, MPH
Oregon Health and Science University
EDITOR’S NOTE: We thank Dr. Prasad for calling this important point to our attention. The online version of this article has been revised to reflect Dr. Prasad’s remarks. It now concludes with the following sentence: “Based on available evidence, we advised our patient, G.B., that it is safe to take shiitake mushroom if she wishes, but there is no evidence to indicate this will boost her immune system.”
1. Dai X, et al: Consuming Lentinula edodes (shiitake) mushrooms daily improves human immunity. J Am Coll Nutr 34:478-487, 2015.
2. Bland JM, Altman DG: Comparisons against baseline within randomised groups are often used and can be highly misleading. Trials 12:264, 2011.