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

This study was conducted as a randomised, double-blind, placebo-controlled, parallel-group external pilot trial. Trained athletes were allocated in a 1:1 ratio to a probiotic group or a placebo group for 28 days.

Participants assigned to the probiotic group consumed one Elite Pro 20 Biotic capsule daily. Each capsule provided 20 billion colony-forming units and contained Bifidobacterium lactis Bl-04, Lactobacillus paracasei Lpc-37, Lactobacillus acidophilus NCFM, Bifidobacterium lactis Bi-07 and Bifidobacterium bifidum Bb-02. Participants assigned to the control group consumed one visually matched capsule containing rice flour daily. Participants and investigators remained blinded to treatment allocation during data collection.

Participants completed daily upper respiratory symptom and training-monitoring records throughout the intervention. Saliva samples were collected at baseline and after 28 days, both before and immediately after a standardised treadmill exercise challenge. Salivary secretory immunoglobulin A was assessed as a marker of mucosal immunity.

The principal purpose of this external pilot was to assess study feasibility, including recruitment, retention, supplementation adherence, capsule return and completion of monitoring records. Salivary secretory immunoglobulin A and upper respiratory symptom outcomes were examined to generate preliminary estimates and inform the methods and sample-size planning of a future definitive trial. A conventional efficacy-based sample-size calculation was therefore not undertaken, and the outcome findings were considered exploratory and hypothesis-generating.

Inclusion criteria

• Male trained athletes aged 18-40 years.
• Regularly participating in structured training and/or competitive sport.
• Apparently healthy at enrolment, with no acute illness or injury that would prevent completion of the exercise testing protocol.
• Able to complete high-intensity treadmill exercise testing.
• Willing to consume the assigned supplement daily for the full intervention period.
• Willing to avoid probiotic supplements, prebiotic supplements, and other new immune- or gut-health-related supplements during the study period.
• Willing and able to provide saliva samples and complete daily upper respiratory symptom monitoring.
• Able to provide written informed consent.

Exclusion criteria

• Current acute respiratory, gastrointestinal, or systemic illness at enrolment.
• Use of antibiotics within the previous 4 weeks.
• Regular use of probiotic or prebiotic supplements before enrolment, unless willing to stop before and during the study period.
• Use of medication or supplements likely to affect immune, inflammatory, gastrointestinal, or salivary biomarker outcomes.
• Known chronic gastrointestinal disease, immune disorder, metabolic disease, cardiovascular disease, or other medical condition that could affect study outcomes or exercise safety.
• Known allergy or intolerance to any ingredient in the probiotic or placebo capsule.
• Current smoker or regular nicotine user.
• Any musculoskeletal injury or health condition limiting maximal or high-intensity treadmill exercise.
• Participation in another intervention study during the study period.
• Inability or unwillingness to comply with the study procedures.