This study is designed as a randomized, double-blind, placebo-controlled human intervention trial among university students with persistent allergic rhinitis (AR) symptoms. The aim is to evaluate the effectiveness of yeast postbiotics in alleviating persistent AR symptoms and to explore the potential mechanisms by which yeast postbiotics modulate the gut microbiota to improve AR-related outcomes. A stratified randomization method will be applied to assign participants into the yeast postbiotic group and the placebo group. Stratification will be based on(1) Sex (male/female), and (2) Physician-diagnosed AR status (yes/no, based on self-reported clinical history), ensuring comparability between the two groups. During the intervention period, participants in the yeast postbiotic group will take two capsules of yeast postbiotic supplements daily after meals, while the placebo group will take two placebo capsules, identical in appearance and composition except without the active ingredients. The total study duration is 15 weeks, including a 1-week run-in period, 12-week intervention, and 2-week follow-up after the intervention.
All participants will be asked to complete a daily nasal symptom score (TNSS) and report any adverse events. At week 0, week 4, and week 12, follow-up assessments will be conducted, including: symptom and quality-of-life questionnaires (e.g., VAS, RQLQ), dietary intake surveys, anthropometric measurements (height, weight, body fat percentage), and biological sample collection (including blood, urine, saliva, and feces). Additionally, saliva samples will be collected specifically at week 2 of the intervention to assess mucosal immune markers.
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;
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;
Parallel
Yeast Postbiotics
Dietary supplementParticipants in the intervention group will take two capsules of yeast postbiotics daily after meals, with each capsule containing 250 mg of yeast postbiotics, along with maltodextrin and silicon dioxide.
Placebo
Dietary supplementParticipants in the placebo group will take an equal number of placebo capsules, identical in dosage form, taste, appearance, and packaging. The placebo contains only maltodextrin and a small amount of silicon dioxide. All participants will take two capsules once daily, swallowed with warm water after meals.
Total Nasal Symptom Score (TNSS)
A scoring system to evaluate the severity of four nasal symptoms: nasal itching, sneezing, rhinorrhea, and nasal congestion. Each symptom is rated on a scale of 0 to 3, with a total score ranging from 0 to 12. Higher scores indicate more severe symptoms.
Visual Analogue Scale (VAS)
A 10 cm straight-line scale where 0 represents "no symptoms" and 10 represents "worst imaginable symptoms." Participants mark a point on the line based on their subjective perception. It is used to evaluate the overall severity and frequency of allergic rhinitis (AR) symptoms.
Rhinoconjunctivitis Quality of Life Questionnaire (RQLQ)
A validated 28-item questionnaire covering seven domains: daily activities, sleep, nasal symptoms, ocular symptoms, emotional impact, practical problems, and environmental exposure. Each item is scored from 0 to 6; higher scores indicate greater impairment. Changes from baseline to post-intervention scores are used to evaluate improvements in quality of life.
Serum Specific IgE (sIgE)
Measured using Fluorescence Enzyme Immunoassay (FEIA), such as ImmunoCAP, to detect IgE antibodies specific to common allergens. A result ≥0.35 kU/L is considered positive, indicating sensitization. It reflects the individual's allergic status and changes over time.
Secretory IgA (sIgA)
Measured in fecal and saliva samples using ELISA kits. sIgA is an indicator of mucosal immune function and plays a role in first-line defense against pathogens.
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