Study of the Effects and Mechanisms of Yeast Postbiotics on Persistent Allergic Rhinitis Symptoms

Allergic rhinitis (AR) is a chronic, non-infectious inflammatory disease of the nasal mucosa mediated by immunoglobulin E (IgE) in atopic individuals after exposure to allergens. Typical clinical manifestations include paroxysmal sneezing, clear nasal discharge, nasal itching, and nasal congestion, often accompanied by itchy eyes, tearing, sleep disturbances, and decreased quality of life. AR is one of the most common chronic nasal diseases in clinical practice, affecting approximately 10%-20% of the global population, and has been recognized by the World Health Organization as a major public health issue.

This study is a randomized, double-blind, placebo-controlled human intervention trial among university students with persistent allergic rhinitis symptoms. It aims to evaluate the efficacy of yeast postbiotics in improving persistent AR symptoms and to explore the potential mechanisms through which yeast postbiotics may alleviate AR symptoms by modulating the gut microbiota. A total of 80 volunteers with persistent AR symptoms will be recruited and randomly assigned to the yeast postbiotic intervention group (n = 40) or the placebo group (n = 40). Both participants and investigators will be blinded to group allocation. The randomization information will only be accessible to the study designers, and all interventions and samples will be coded to prevent unblinding. If a participant experiences a serious adverse event due to the intervention, unblinding will be performed and the participant will be withdrawn from the study During the intervention period, participants in the intervention group will take two capsules of yeast postbiotics daily, each containing 250 mg of yeast postbiotics along with appropriate amounts of maltodextrin and silicon dioxide. The placebo group will take two capsules per day of an identically appearing placebo, which contains only maltodextrin and a small amount of silicon dioxide. All participants will take the capsules once daily after meals with warm water. All participants will complete a daily Total Nasal Symptom Score (TNSS) and report any adverse events. Follow-ups will be conducted at Week 0, Week 4, and Week 12, including questionnaire assessments (VAS, RQLQ), dietary surveys, anthropometric measurements (height, weight, body fat percentage), and biological sample collection (blood, urine, saliva, and stool). A saliva sample will also be collected at Week 2.

The primary outcome of this study is TNSS. Secondary outcomes include: Visual Analogue Scale (VAS), Rhinoconjunctivitis Quality of Life Questionnaire (RQLQ), Serum specific IgE (sIgE), Secretory IgA (sIgA), Inflammatory cytokines (IFN-γ, IL-4, IL-10, IL-6, and TNF-α), Gut microbiota composition, Serum biochemical indicators (CRP, ALT/AST, BUN/Cr). Statistical analysis will be conducted using SAS 9.4 software. Continuous variables will be expressed as mean ± standard deviation, and ordinal variables as proportions. T-tests and Kruskal-Wallis rank-sum tests will be used to compare continuous variables. Chi-square tests or Fisher's exact tests will be used for categorical variables. A p-value < 0.05 will be considered statistically significant. For outcome variables measured at multiple time points (e.g., VAS scores, cytokine levels at Weeks 0, 4, and 12), linear mixed-effects models (LMMs) will be constructed to assess the effects of time, group, and interaction, and to compare the trends across different time points between the intervention and control groups.

Inclusion criteria

• Aged between 18 and 35 years;
• Meeting the symptom criteria for persistent allergic rhinitis (AR) as defined in the Chinese Guidelines for Diagnosis and Treatment of Allergic Rhinitis (2022, Revised Edition): (1) Symptoms: Two or more of the following-paroxysmal sneezing, watery rhinorrhea, nasal itching, and nasal congestion-lasting continuously or cumulatively for at least 1 hour per day; ocular symptoms such as tearing, itching, and redness may also be present; (2) Persistent AR: Symptoms occur on ≥4 days per week and persist for ≥4 consecutive weeks;
• No use of probiotics, prebiotics, synbiotics, antihistamines, corticosteroids, or immunosuppressants within 1 month prior to screening;
• Willing and able to maintain usual physical activity levels and dietary patterns during the study;
• Able and willing to sign the informed consent form voluntarily.

Exclusion criteria

• Use of antibiotics, osmotic laxatives (e.g., magnesium sulfate, lactulose), anthraquinone-containing agents (e.g., rhubarb, aloe, senna), or gastrointestinal motility-promoting drugs (e.g., metoclopramide, domperidone, cisapride) within 1 month prior to screening;
• Diagnosed with non-allergic rhinitis (e.g., vasomotor rhinitis, infectious rhinitis, hormonal rhinitis, drug-induced rhinitis), or with nasal polyps, severe nasal septum deviation, cerebrospinal fluid rhinorrhea, or aspirin-exacerbated respiratory disease (AERD);
• Patients with uncontrolled allergic comorbidities, including sinusitis, otitis media, allergic asthma, or atopic dermatitis;
• History of serious gastrointestinal diseases (e.g., severe diarrhea, inflammatory bowel disease), or gastrointestinal endoscopy within the past month;
• Diagnosed with congenital genetic disorders, primary immunodeficiency diseases, severe systemic illnesses, or malignancies;
• Pregnant or lactating women, or women with plans to conceive during the study period.