Multi-Strain Probiotic Supplementation, Salivary Immunity, and Upper Respiratory Symptoms in Trained Athletes

This completed external pilot study assessed the feasibility of conducting a randomised, double-blind, placebo-controlled trial of four-week multi-strain probiotic supplementation in trained athletes. Participants were allocated to receive either one probiotic capsule containing 20 billion colony-forming units or a matched rice-flour placebo capsule daily for 28 days. Feasibility measures included recruitment, retention, supplementation adherence and completion of daily monitoring records. Preliminary biological and symptom outcomes included salivary secretory immunoglobulin A and upper respiratory symptom burden. The findings were intended to inform the design of a future definitive randomised controlled trial and were not intended to provide a definitive assessment of efficacy.