Soluble and Insoluble Yeast β-Glucan Differentially Affect Upper Respiratory Tract Infection in Marathon Runners: A Double-Blind, Randomized Placebo-Controlled Trial

In a previous study, consumption of a dairy beverage incorporating insoluble beta-glucan decreased upper respiratory tract infection (URTI) symptomatic days and severity in marathon runners. In this report, we extended our previous findings by presenting data on a dairy beverage containing soluble beta-glucan and URTI in marathon runners. Healthy adults running in the 2017 Austin Marathon consumed dairy beverages (250 mL/day) containing 250 mg of insoluble (n = 69) or soluble (n = 76) baker's yeast beta-glucan (Wellmune (R)) or placebo (n = 133) for the 45 days before, day of, and 45 days after the marathon (91 days total). Participants completed a daily online survey assessing compliance and URTI symptoms, which were evaluated using the Jackson Index and confirmed by the study physician. Total severity of URTI was significantly lower in the insoluble yeast beta-glucan group compared to the placebo group, but was not different between the soluble yeast beta-glucan group and placebo group. Severity ratings for nasal discharge were significantly lower in both the insoluble and soluble yeast beta-glucan groups compared to the placebo group. Additionally, severity rating for sore throat was lower in the insoluble, but not the soluble yeast beta-glucan group compared to the placebo group. The insoluble yeast beta-glucan group, but not the soluble yeast beta-glucan group also reported fewer URTI symptomatic days compared to the placebo group. The results suggest that soluble and insoluble yeast beta-glucan, incorporated into a food matrix, differentially affected exercise-induced URTI in marathon runners.