Study of the Preventive Effects and Mechanisms of Yeast β-Glucan on Upper Respiratory Tract Infections

Upper respiratory tract infections (URTIs) are acute mucosal infectious diseases caused by the invasion of respiratory mucosa by pathogens, which disrupt the mucosal barrier, activate the immune system, and trigger inflammatory responses. Clinical symptoms include nasal congestion, rhinorrhea, sore throat, cough, and hoarseness. Although URTIs are generally self-limiting, their high incidence, recurrence, and transmissibility-especially in crowded settings such as schools and workplaces-pose a significant public health burden. Allergic rhinitis (AR) is a chronic upper airway inflammatory disease mediated by immunoglobulin E (IgE), with typical symptoms such as nasal itching, sneezing, clear rhinorrhea, and nasal congestion. In AR patients, the nasal mucosa remains in a persistent inflammatory state, with impaired epithelial barrier function, reduced ciliary activity, and decreased local secretory IgA (sIgA) production. These alterations weaken the mucosal immune defense against viruses and bacteria, making AR patients more prone to recurrent URTIs. Furthermore, the seasonal onset of AR often coincides with peak URTI incidence, further compounding the risk of infection. Therefore, individuals with AR are considered a susceptible population for URTIs and are ideal targets for evaluating preventive interventions.

This study is designed as a randomized, double-blind, placebo-controlled human intervention trial among university students with persistent AR symptoms. The aim is to evaluate the preventive effect and underlying mechanisms of yeast β-glucan on URTIs, providing scientific evidence for the prophylactic application of prebiotics in high-risk populations. A total of 96 participants with persistent AR symptoms will be recruited and stratified by sex and BMI before being randomly assigned to either the yeast β-glucan group (n=48) or the placebo group (n=48). Blinding will be applied to both participants and investigators. Only the study designers will have access to the randomization codes. All intervention products and samples will be labeled with coded identifiers to prevent unblinding. If a participant experiences a serious adverse event related to the intervention, unblinding will be permitted, and the participant will be withdrawn from the study.

The yeast β-glucan used in this study is provided by Angel Yeast Co., Ltd. In 2010, China's Ministry of Health approved yeast β-glucan as a novel food ingredient for use in general food products, indicating its established safety. Nevertheless, adverse events will be closely monitored throughout the study and reported in accordance with ethical requirements.

During the intervention period, participants in the intervention group will take two yeast β-glucan capsules daily, each containing 250 mg of yeast β-glucan along with maltodextrin and silicon dioxide. The placebo group will receive identical capsules in terms of form, taste, appearance, and packaging, containing only maltodextrin and a small amount of silicon dioxide. All participants will take two capsules once daily after meals with warm water. Participants will be monitored daily for the occurrence of URTIs. If URTIs occur, the Wisconsin Upper Respiratory Symptom Survey (WURSS-24) will be used to assess symptom severity and duration, and medication use (number of doses, dosage, and timing) will be recorded. Weekly follow-ups will be conducted to assess Total Nasal Symptom Score (TNSS), Rhinoconjunctivitis Quality of Life Questionnaire (RQLQ), and adverse events. At weeks 0 and 12, participants will complete questionnaire assessments (TNSS, RQLQ), a dietary intake survey, anthropometric measurements (e.g., height, weight, body fat percentage), and biological sample collection (blood, urine, and feces).

The primary outcome of this study is the incidence of URTIs. Secondary outcomes include: WURSS-24 (URTI symptom severity and duration), TNSS (nasal symptom score), RQLQ (quality of life assessment for rhinoconjunctivitis) ,Inflammatory cytokines (IFN-γ, IL-4, IL-10, IL-6, TNF-α) Serum biochemical markers(CRP, ALT/AST, BUN/Cr) and Fecal biomarkers (microbiota composition, SCFAs). Data will be analyzed using SAS 9.4 software. Continuous variables will be expressed as mean ± standard deviation; ordinal variables will be presented as percentages. Independent sample t-tests or Kruskal-Wallis tests will be used for continuous variables, and chi-square or Fisher's exact tests will be used for categorical variables. A p-value of < 0.05 will be considered statistically significant. For outcome variables with repeated measures at multiple time points (e.g., TNSS, inflammatory markers at weeks 0 and 12), a linear mixed-effects model (LMM) will be constructed to evaluate the effects of time, group, and their interaction, and to compare temporal trends between the intervention and control groups.