Fermented Milk Drink With Lacticaseibacillus Paracasei Strain Shirota Helps Triathletes With Cold-Like Symptoms Before and After a Race

Background: Endurance athletes are frequently exposed to high physical stress, which may lead to temporary immune suppression and increased susceptibility to upper respiratory tract infections (URTIs). Previous studies suggest that probiotics may play a role in supporting the immune system. Objective: To assess the efficacy of a fermented milk drink containing Lacticaseibacillus paracasei strain Shirota (LCS) in reducing upper airway symptoms in triathletes before and after a competitive event. Study Design: This is a multi-center, double-blind, randomized, placebo-controlled, parallel-group study. Eligible participants will be healthy adult triathletes preparing for a scheduled race. They will be randomized to consume either the probiotic drink or a placebo daily, starting several weeks before the race and continuing for a defined recovery period afterward. Primary Outcome: -Salivary IgA Concentration The primary outcome is the change in salivary immunoglobulin A (IgA) concentration before and after the competition, assessed at five time points. This measure will reflect mucosal immune function and the potential modulatory effect of daily intake of fermented milk containing Lacticaseibacillus paracasei strain Shirota. Secondary Outcomes: * Systemic Immune and Inflammatory Response Blood samples will be analyzed for markers of systemic immune activation and inflammation (e.g., cytokines), collected at five time points to evaluate the broader immunomodulatory effects of the probiotic intervention. * Upper Airway Symptoms Incidence, severity, and duration of upper airway symptoms (e.g., sore throat, cough, nasal congestion) will be assessed using the Wisconsin Upper Respiratory Symptom Survey-21 (WURSS-21). Higher scores indicate more severe symptoms and a greater impact on daily functioning. * Mood State Mood state changes will be evaluated using the Brunel Mood Scale (BRUMS) across six subscales. Total Mood Disturbance (TMD) scores will reflect the psychological response to training and competition. Higher scores indicate worse mood states.