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

NCT07782983 | Completed

• 1 other identifier: REC.24.0071
• Study Type: interventional
• Target: 15
• Locations: 1 country
• Sites: 1

Brief Summary

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.

Conditions

Upper Respiratory Symptoms; Mucosal Immunity

Keywords

Probiotics; Trained Athletes; Salivary Secretory Immunoglobulin A; sIgA; Upper Respiratory Symptoms; Mucosal Immunity; Exercise Immunology; External Pilot Randomized Controlled Trial

Outcome Measures

Primary Outcomes (1)

• Resting Salivary Secretory Immunoglobulin A Concentration

  Saliva was collected immediately before a standardised treadmill exercise challenge at baseline and after 28 days of supplementation. Secretory immunoglobulin A concentration was measured using an enzyme-linked immunosorbent assay. Day 28 resting sIgA was compared between groups while accounting for baseline resting sIgA.

  Baseline and Day 28

Study Arms (2)

Probiotic

EXPERIMENTAL

Participants received one Elite Pro 20 Biotic multi-strain probiotic capsule containing 20 billion CFU once daily for 28 days.

Dietary Supplement: Multi-Strain Probiotic

Placebo

PLACEBO COMPARATOR

Participants received one visually matched capsule containing rice flour once daily for 28 days.

Dietary Supplement: Rice Flour Placebo

Interventions

Multi-Strain Probiotic DIETARY_SUPPLEMENT

One oral capsule was taken daily for 28 days. Each capsule provided 20 billion colony-forming units and contained Lactobacillus acidophilus NCFM, Lactobacillus paracasei Lpc-37, Bifidobacterium lactis Bl-04, Bifidobacterium lactis Bi-07, and Bifidobacterium bifidum Bb-02

Probiotic

Rice Flour Placebo DIETARY_SUPPLEMENT

One visually matched oral capsule containing rice flour and no live microorganisms was taken daily for 28 days.

Placebo

Eligibility Criteria

• Age: 18 Years - 40 Years
• Gender Eligibility Details: Biologically assigned birth is eligibility
• Healthy Volunteers: Yes
• Age Groups: Adult (18-64)

You may qualify if:

• 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.

You may not qualify if:

• 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.

Sponsors & Collaborators

• University of Ulster: lead

Study Sites (1)

Ulster University Belfast Campus, Human Physiology Laboratory, Room BC-04-409

Belfast, Northern Ireland, BT15 1ED, United Kingdom

Location

MeSH Terms

Conditions

Signs and Symptoms, Respiratory

Condition Hierarchy (Ancestors)

Signs and Symptoms; Pathological Conditions, Signs and Symptoms

Study Officials

• Andrea McNeilly, PhD

  Ulster University

  PRINCIPAL INVESTIGATOR

Study Design

• Study Type: interventional
• Phase: not applicable
• Allocation: RANDOMIZED
• Masking: DOUBLE
• Who Masked: PARTICIPANT, INVESTIGATOR
• Purpose: PREVENTION
• Intervention Model: PARALLEL
• Sponsor Type: OTHER
• Responsible Party: SPONSOR

Model Details: Participants were randomly assigned in a 1:1 ratio to receive either a multi-strain probiotic capsule or a matched rice-flour placebo capsule once daily for 28 days.

Study Record Dates

• First Submitted: August 19, 2026
• First Posted: August 24, 2026
• Study Start: May 13, 2025
• Primary Completion: December 19, 2025
• Study Completion: December 19, 2025
• Last Updated: August 24, 2026

Record last verified: 2026-08

Data Sharing

• IPD Sharing: Will not share

Locations

GB (1)