A novel role of probiotics in improving host defence of elite rugby union athlete: A double blind randomised controlled trial

A systematic scoping review of study methodology for randomized controlled trials investigating probiotics in athletic and physically active populations

BACKGROUND

The purported ergogenic and health effects of probiotics have been a topic of great intrigue among researchers, practitioners, and the lay public alike. There has also been an increased research focus within the realm of sports science and exercise medicine on the athletic gut microbiota. However, compared to other ergogenic aids and dietary supplements, probiotics present unique study challenges. The objectives of this systematic scoping review were to identify and characterize study methodologies of randomized controlled trials investigating supplementation with probiotics in athletes and physically active individuals.

METHODS

Four databases (MEDLINE, CINAHL, Cochrane CENTRAL, and Cochrane Database of Systematic Reviews) were searched for randomized controlled studies involving healthy athletes or physically active individuals. An intervention with probiotics and inclusion of a control and/or placebo group were essential. Only peer-reviewed articles in English were considered, and there were no date restrictions. Results were extracted and presented in tabular form to detail study protocols, characteristics, and outcomes. Bias in randomized controlled trials was determined with the RoB 2.0 tool.

RESULTS

A total of 45 studies were included in the review, with 35 using a parallel group design and 10 using a cross-over design. Approximately half the studies used a single probiotic and the other half a multi-strain preparation. The probiotic dose ranged from 2 × 108 to 1 × 1011 colony forming units daily, and the length of intervention was between 7 and 150 days. Fewer than half the studies directly assessed gastrointestinal symptoms, gut permeability, or the gut microbiota. The sex ratio of participants was heavily weighted toward males, and only 3 studies exclusively investigated females. Low-level adverse events were reported in only 2 studies, although the methodology of reporting varied widely. The risk of bias was generally low, although details on randomization were lacking in some studies.

CONCLUSION

There is a substantial body of research on the effects of probiotic supplementation in healthy athletes and physically active individuals. Considerable heterogeneity in probiotic selection and dosage as well as outcome measures has made clinical and mechanistic interpretation challenging for both health care practitioners and researchers. Attention to issues of randomization of participants, treatments and interventions, selection of outcomes, demographics, and reporting of adverse events will facilitate more trustworthy interpretation of probiotic study results and inform evidence-based guidelines.

Orally Ingested Probiotic, Prebiotic, and Synbiotic Interventions as Countermeasures for Gastrointestinal Tract Infections in Nonelderly Adults: A Systematic Review and Meta-Analysis

Meta-analyses have not examined the prophylactic use of orally ingested probiotics, prebiotics, and synbiotics for preventing gastrointestinal tract infections (GTIs) of various etiologies in adult populations, despite evidence that these gut microbiota-targeted interventions can be effective in treating certain GTIs. This systematic review and meta-analysis aimed to estimate the effects of prophylactic use of orally ingested probiotics, prebiotics, and synbiotics on GTI incidence, duration, and severity in nonelderly, nonhospitalized adults. CENTRAL, PubMed, Scopus, and Web of Science were searched through January 2022. English-language, peer-reviewed publications of randomized, placebo-controlled studies testing an orally ingested probiotic, prebiotic, or synbiotic intervention of any dose for ≥1 wk in adults who were not hospitalized, immunosuppressed, or taking antibiotics were included. Results were analyzed using random-effects meta-analyses of intention-to-treat (ITT) and complete case (CC) cohorts. Heterogeneity was explored by subgroup meta-analysis and meta-regression. The risk of bias was assessed using the Cochrane risk-of-bias 2 tool. Seventeen publications reporting 20 studies of probiotics (n = 16), prebiotics (n = 3), and synbiotics (n = 1) were identified (n > 6994 subjects). In CC and ITT analyses, risk of experiencing ≥1 GTI was reduced with probiotics (CC analysis-risk ratio: 0.86; 95% CI: 0.73, 1.01) and prebiotics (risk ratio: 0.80; 95% CI: 0.66, 0.98). No effects on GTI duration or severity were observed. Sources of heterogeneity included the study population and number of probiotic strains administered but were often unexplained, and a high risk of bias was observed for most studies. The specific effects of individual probiotic strains and prebiotic types could not be assessed owing to a lack of confirmatory studies. Findings indicated that both orally ingested probiotics and prebiotics, relative to placebo, demonstrated modest benefit for reducing GTI risk in nonelderly adults. However, results should be interpreted cautiously owing to the low number of studies, high risk of bias, and unexplained heterogeneity that may include probiotic strain-specific or prebiotic-specific effects. This review was registered at PROSPERO as CRD42020200670.

Orally Ingested Probiotics, Prebiotics, and Synbiotics as Countermeasures for Respiratory Tract Infections in Nonelderly Adults: A Systematic Review and Meta-Analysis

The impact of gut microbiota-targeted interventions on the incidence, duration, and severity of respiratory tract infections (RTIs) in nonelderly adults, and factors moderating any such effects, are unclear. This systematic review and meta-analysis aimed to determine the effects of orally ingested probiotics, prebiotics, and synbiotics compared with placebo on RTI incidence, duration, and severity in nonelderly adults, and to identify potential sources of heterogeneity. Studies were identified by searching CENTRAL, PubMed, Scopus, and Web of Science up to December 2021. English-language, peer-reviewed publications of randomized, placebo-controlled studies that tested an orally ingested probiotic, prebiotic, or synbiotic intervention of any dose for ≥1 wk in adults aged 18-65 y were included. Results were synthesized using intention-to-treat and per-protocol random-effects meta-analysis. Heterogeneity was explored by subgroup meta-analysis and meta-regression. Risk of bias was assessed using the Cochrane risk-of-bias assessment tool for randomized trials version 2 (RoB2). Forty-two manuscripts reporting effects of probiotics (n = 38), prebiotics (n = 2), synbiotics (n = 1) or multiple -biotic types (n = 1) were identified (n = 9179 subjects). Probiotics reduced the risk of experiencing ≥1 RTI (relative risk = 0.91; 95% CI: 0.84, 0.98; P = 0.01), and total days (rate ratio = 0.77; 95% CI: 0.71, 0.83; P < 0.001), duration (Hedges' g = -0.23; 95% CI: -0.39, -0.08; P = 0.004), and severity (Hedges' g = -0.16; 95% CI: -0.29, -0.03; P = 0.02) of RTIs. Effects were relatively consistent across different strain combinations, doses, and durations, although reductions in RTI duration were larger with fermented dairy as the delivery matrix, and beneficial effects of probiotics were not observed in physically active populations. Overall risk of bias was rated as "some  concerns" for most studies. In conclusion, orally ingested probiotics, relative to placebo, modestly reduce the incidence, duration, and severity of RTIs in nonelderly adults. Physical activity and delivery matrix may moderate some of these effects. Whether prebiotic and synbiotic interventions confer similar protection remains unclear due to few relevant studies. This trial was registered at https://www.crd.york.ac.uk/prospero/ as CRD42020220213.

Effects of Probiotics Supplementation on Risk and Severity of Infections in Athletes: A Systematic Review

The aim of this review was to appraise the literature on the effects of probiotics supplementation on gastrointestinal (GI) and upper respiratory tract infection (URTI) risk and prognosis in athletes. The search was conducted using the following electronic databases: MEDLINE (PubMed); Web of Science; Scopus; and SPORTDiscus (EBSCO). According to the PRISMA guidelines, randomized controlled studies performed on healthy athletes with a note dose of probiotics supplementation were considered. From the 2304 articles found, after eliminating reviews and studies on animals and unhealthy subjects and after screening of titles and abstracts, 403 studies were considered eligible. From these, in accordance with the inclusion and exclusion criteria, 16 studies were selected, ten of which concerned endurance athletes. The majority of the studies reported beneficial effects of probiotics in reducing the risk of developing the examined infections or the severity of related symptoms. However, due to the differences in formulations used and populations analyzed in the available studies, further research is needed in this field to achieve stronger and more specific evidence.

Effects of Probiotics Supplementation on Gastrointestinal Symptoms in Athletes: A Systematic Review of Randomized Controlled Trials

This study examines the effectiveness of probiotic supplementation on gastrointestinal (GI) symptoms, the gut barrier function, and inflammatory markers in athletes based on data from randomised controlled trials. Searches were conducted in PubMed, the Cochrane Library, and the Web of Science up to October 2021. The protocol for this review was registered with PROSPERO (CRD42021284938). Two reviewers independently screened the titles, abstracts, and full texts to identify articles on the influence of probiotics or symbiotics on GI symptoms, gut barrier function, and cytokines, and the quality of the studies was assessed using RoB2. Ten articles involving 822 athletes were included in this review. A single strain Lactobacillus bacteria was used in three studies, seven studies used a Lactobacillus and Bifidobacterium multi-strain cocktail, and one study used this cocktail with a prebiotic. Only slight evidence was found for a positive effect of probiotics on GI symptoms in athletes during training, exercise, and competition, so it was not possible to identify the best product for managing GI symptoms in athletes. Due to the small number of studies, it was also difficult to find a direct association between the reduced exercise-induced perturbations in cytokines, gut barrier function, and GI symptoms after probiotic supplementation.

PROBIOTIC SUPPLEMENTS FOR ENDURANCE EXERCISE PERFORMANCE AND IMMUNE FUNCTION

ABSTRACT Introduction: After long-term research, it was found that athletes are susceptible to suffering from upper respiratory tract infections and digestive system diseases when subjected to high-intensity exercise for long periods. Objective: To verify whether consuming probiotic supplements after exercise can significantly improve the function of the immune system and play a positive role in the health of athletes. Method: This is a quantitative study with distribution analysis to verify whether probiotic supplements could improve immune response after exercise. Results: After using probiotic supplements, by recording the individual differences in the distribution characteristics of athletes› gastrointestinal flora, we found that the changes of subjects› sports performance, leukocytes, neutrophils, lymphocytes, and gastrointestinal flora after six weeks of special training were different. Conclusion: Long-term oral probiotics for athletes can effectively reduce inflammation in the body, reduce damage to the body during exercise, and effectively improve the gastrointestinal tract›s immune function. Level of evidence II; Therapeutic studies - investigation of treatment results.

Incidence of acute respiratory illnesses in athletes: a systematic review and meta-analysis by a subgroup of the IOC consensus on 'acute respiratory illness in the athlete'

OBJECTIVE

To determine the incidence of acute respiratory illness (ARill) in athletes and by method of diagnosis, anatomical classification, ages, levels of performance and seasons.

DESIGN

Systematic review and meta-analysis.

DATA SOURCES

Electronic databases: PubMed-Medline, EbscoHost and Web of Science.

ELIGIBILITY CRITERIA

Original research articles published between January 1990 and July 2020 in English reporting the incidence of ARill in athletes, at any level of performance (elite/non-elite), aged 15-65 years.

RESULTS

Across all 124 studies (n=1 28 360 athletes), the incidence of ARill, estimated by dividing the number of cases by the total number of athlete days, was 4.7 (95% CI 3.9 to 5.7) per 1000 athlete days. In studies reporting acute respiratory infections (ARinf; suspected and confirmed) the incidence was 4.9 (95% CI 4.0 to 6.0), which was similar in studies reporting undiagnosed ARill (3.7; 95% CI 2.1 to 6.7). Incidences of 5.9 (95% CI 4.8 to 7.2) and 2.8 (95% CI 1.8 to 4.5) were found for studies reporting upper ARinf and general ARinf (upper or lower), respectively. The incidence of ARinf was similar across the different methods to diagnose ARinf. A higher incidence of ARinf was found in non-elite (8.7; 95% CI 6.1 to 12.5) vs elite athletes (4.2; 95% CI 3.3 to 5.3).

SUMMARY/CONCLUSIONS

These findings suggest: (1) the incidence of ARill equates to approximately 4.7 per athlete per year; (2) the incidence of upper ARinf was significantly higher than general (upper/lower) ARinf; (3) elite athletes have a lower incidence of ARinf than non-elite athletes; (4) if pathogen identification is not available, physicians can confidently use validated questionnaires and checklists to screen athletes for suspected ARinf. For future studies, we recommend that a clear diagnosis of ARill is reported.

PROSPERO REGISTRATION NUMBER

CRD42020160472.

Health Benefits of Probiotics in Sport and Exercise - Non-existent or a Matter of Heterogeneity? A Systematic Review

Background

The use of probiotics in sports has been growing in recent years, as up to 50% of athletes suffer from training- and performance-limiting gastrointestinal (GI) problems. Moreover, repeated exhaustive exercise and high training loads may lead to a transiently depressed immune function, associated with an increased risk of upper respiratory tract infection (URTI).

Aim

To provide a qualitative analysis of probiotic effects on URTI, GI symptoms and the immune system in healthy individuals under consideration of performance level as main classifier.

Methods

A systematic review of the literature was conducted (PubMed, SPORTDiscus with Full Text, Web of Science) to analyze the effects of probiotics in athletes and healthy active individuals on GI problems, URTI, and the immune system. A qualitative synthesis with performance level and treatment duration as main classifiers was performed.

Results

Of 41 eligible studies, 24 evaluated the effects of probiotic supplements in athletes, 10 in recreationally active individuals and 7 in healthy untrained adults. Large heterogeneity was observed in terms of probiotic strains, mode of delivery, performance level, treatment duration and outcome assessment. Overall, studies provided inconsistent observations.

Conclusion

The effects of probiotics on immune system, URTI, and GI symptoms in athletes, healthy adults and recreationally active individuals remain inconclusive. Based on the analyzed studies and identified parameters, this article provides suggestions to align future research on the effects of probiotics in exercise.

Systematic Review Registration

PROSPERO, identifier: CRD42021245840.

Effect of Probiotic Consumption on Immune Response in Athletes: A Meta-analysis

The possible effect of probiotic interventions on immunological markers in athletes is inconclusive. Therefore, to synthesize and quantitatively analyze the existing evidence on this topic, systematic literature searches of online databases PubMed, Scopus, Cochrane Library, and ISI Web of Sciences was carried out up to February 2021 to find all randomized controlled trials (RCTs) concerning the immunological effects of probiotics in athletes. In the random-effects model, weighted mean difference (WMD) and 95% confidence interval (CI) explained the net effect. The authors assessed the likelihood of publication bias via Egger's and Begg's statistics. A total of 13 RCTs (836 participants) were retrieved. Probiotic consumption reduced lymphocyte T cytotoxic count significantly (WMD=-0.08 cells×10⁹/L; 95% CI: -0.15 to -0.01; p=0.022) with evidence of moderate heterogeneity (I ²⁼59.1%, p=0.044) and monocyte count when intervention duration was ≤ 4 weeks (WMD=-0.08 cells×10⁹/L; 95% CI: -0.16 to -0.001; I ²⁼0.0%). Furthermore, leukocyte count was significantly elevated (WMD=0.48 cells×10⁹/L; 95% CI: 0.02 to 0.93; I ²⁼0.0%) when multi-strain probiotics were used. Probiotic supplements may improve immunological markers, including lymphocyte T cytotoxic, monocyte, and leukocyte in athletes. Further randomized controlled trials using diverse strains of probiotics and consistent outcome measures are necessary to allow for evidence-based recommendations.

Effects of probiotic supplementation on respiratory infection and immune function in athletes: systematic review and meta-analysis of randomized controlled trials

OBJECTIVE

The aim of this study was to evaluate the effectiveness of probiotic supplementation on upper tract respiratory infection and inflammatory markers in elite athletes.

DATA SOURCES

We identified sources by searching the PubMed, EBSCO host, Scopus, and Web of Science databases using the following search terms: "probiotic" OR "probiotics" AND "exercise" OR "sport" OR "athletes" AND "URTI" OR "respiratory infection" OR "upper respiratory tract infections" OR "inflammation" OR "inflammatory OR "cytokines".

STUDY SELECTION

We screened the title and abstracts of 2498 articles using our inclusion critieria. A total of 14 articles were selected for further analysis.

DATA EXTRACTION

Data from the included studies were extracted by 2 independent reviewers. These data included the study design, participant characteristics, inclusion and exclusion, intervention characteristics, outcome measures, and the main results of the study.

DATA SYNTHESIS

The meta-analysis did not show any significant effect of probiotic supplementation on the number of days of illness or the mean number and duration of URTI episodes, but there was a significant effect of probiotic supplementation on total symptom severity score (-0.65, 95% CI: -1.05; -0.25, p = 0.02). Lower levels of IL-6 (-2.52 pg/ml, 95% CI: -4.12, -0.51, p = 0.001) and TNF-α (-2.31 pg/ml, 95% CI: -4.12, -0.51, p = 0.008) were also reported after supplementation.

CONCLUSIONS

This meta-analysis provides evidence that probiotic supplementation, especially among professional athletes, is an effective way to decrease the total URTI symptom severity score. Additionally, probiotic supplementation may decrease TNF-α and IL-6 levels. There is a need for more studies with larger groups to better estimate this effect. It is necessary to determine the best timing, duration, composition and dose of such supplementation.

Probiotics and Gut Health in Athletes

PURPOSE OF REVIEW

To provide a focused analysis of the challenges to gut health in athletes and examine recent research aimed at determining the impact of probiotics on preventing gastrointestinal (GI) symptoms and loss of barrier function in athletes.

RECENT FINDINGS

Frequency and severity of GI symptoms during training or competition were reduced by approximately one-third in studies demonstrating efficacy. Improvement of GI symptoms with probiotic supplementation was measured in both single-strain Lactobacillus and multi-strain Lactobacillus and Bifidobacterim probiotics, while improvement in gut barrier function was only measured for multi-strain probiotics. Likelihood of efficacy increased with duration of supplementation. The greatest efficacy for reducing GI symptom frequency and severity, as well as improving or preserving gut barrier function during exercise training and competition, appears to be for multi-strain Lactobacillus and Bifidobacterium probiotic cocktails supplemented for at least 11 weeks.

Illness and infection in elite full-contact football-code sports: A systematic review

OBJECTIVES

Full-contact football-code team sports offer a unique environment for illness risk. During training and match-play, players are exposed to high-intensity collisions which may result in skin-on-skin abrasions and transfer of bodily fluids. Understanding the incidence of all illnesses and infections and what impact they cause to time-loss from training and competition is important to improve athlete care within these sports. This review aimed to systematically report, quantify and compare the type, incidence, prevalence and count of illnesses across full-contact football-code team sports.

DESIGN/METHODS

A systematic search of Cochrane Library, MEDLINE, SPORTDiscus, PsycINFO and CINAHL electronic databases was performed from inception to October 2019; keywords relating to illness, athletes and epidemiology were used. Studies were excluded if they did not quantify illness or infection, involve elite athletes, investigate full-contact football-code sports or were review articles.

RESULTS

Twenty-eight studies met the eligibility criteria. Five different football-codes were reported: American football (n=10), Australian rules football (n=3), rugby league (n=2), rugby sevens (n=3) and rugby union (n=9). One multi-sport study included both American football and rugby union. Full-contact football-code athletes are most commonly affected by respiratory system illnesses. There is a distinct lack of consensus of illness monitoring methodology.

CONCLUSIONS

Full-contact football-code team sport athletes are most commonly affected by respiratory system illnesses. Due to various monitoring methodologies, illness incidence could only be compared between studies that used matching incidence exposure measures. High-quality illness surveillance data collection is an essential component to undertake effective and targeted illness prevention in athletes.

Recent advances in clinical probiotic research for sport

PURPOSE OF REVIEW

This is a review of the most up-to-date research on the effectiveness of probiotic supplementation for outcomes related to athletes and physical activity. The focus is on clinical research incorporating exercise and/or physically active participants on the nutritional effectiveness of single and multistrain preparations.

RECENT FINDINGS

Findings of the included clinical studies support the notion that certain probiotics could play important roles in maintaining normal physiology and energy production during exercise which may lead to performance-improvement and antifatigue effects, improve exercise-induced gastrointestinal symptoms and permeability, stimulate/modulate of the immune system, and improve the ability to digest, absorb, and metabolize macro and micronutrients important to exercise performance and recovery/health status of those physically active.

SUMMARY

The current body of literature highlights the specificity of probiotic strain/dose and potential mechanisms of action for application in sport. These novel findings open new areas research, potential use for human health, and reinforce the potential role for probiotic's in exercise performance. While encouraging, more well designed studies of probiotic supplementation in various sport applications are warranted.

International Society of Sports Nutrition Position Stand: Probiotics

Position statement: The International Society of Sports Nutrition (ISSN) provides an objective and critical review of the mechanisms and use of probiotic supplementation to optimize the health, performance, and recovery of athletes. Based on the current available literature, the conclusions of the ISSN are as follows: 1)Probiotics are live microorganisms that, when administered in adequate amounts, confer a health benefit on the host (FAO/WHO).2)Probiotic administration has been linked to a multitude of health benefits, with gut and immune health being the most researched applications.3)Despite the existence of shared, core mechanisms for probiotic function, health benefits of probiotics are strain- and dose-dependent.4)Athletes have varying gut microbiota compositions that appear to reflect the activity level of the host in comparison to sedentary people, with the differences linked primarily to the volume of exercise and amount of protein consumption. Whether differences in gut microbiota composition affect probiotic efficacy is unknown.5)The main function of the gut is to digest food and absorb nutrients. In athletic populations, certain probiotics strains can increase absorption of key nutrients such as amino acids from protein, and affect the pharmacology and physiological properties of multiple food components.6)Immune depression in athletes worsens with excessive training load, psychological stress, disturbed sleep, and environmental extremes, all of which can contribute to an increased risk of respiratory tract infections. In certain situations, including exposure to crowds, foreign travel and poor hygiene at home, and training or competition venues, athletes' exposure to pathogens may be elevated leading to increased rates of infections. Approximately 70% of the immune system is located in the gut and probiotic supplementation has been shown to promote a healthy immune response. In an athletic population, specific probiotic strains can reduce the number of episodes, severity and duration of upper respiratory tract infections.7)Intense, prolonged exercise, especially in the heat, has been shown to increase gut permeability which potentially can result in systemic toxemia. Specific probiotic strains can improve the integrity of the gut-barrier function in athletes.8)Administration of selected anti-inflammatory probiotic strains have been linked to improved recovery from muscle-damaging exercise.9)The minimal effective dose and method of administration (potency per serving, single vs. split dose, delivery form) of a specific probiotic strain depends on validation studies for this particular strain. Products that contain probiotics must include the genus, species, and strain of each live microorganism on its label as well as the total estimated quantity of each probiotic strain at the end of the product's shelf life, as measured by colony forming units (CFU) or live cells.10)Preclinical and early human research has shown potential probiotic benefits relevant to an athletic population that include improved body composition and lean body mass, normalizing age-related declines in testosterone levels, reductions in cortisol levels indicating improved responses to a physical or mental stressor, reduction of exercise-induced lactate, and increased neurotransmitter synthesis, cognition and mood. However, these potential benefits require validation in more rigorous human studies and in an athletic population.

Effect of Probiotics Supplementations on Health Status of Athletes

Athletes are prone to several health complications, including upper respiratory tract infections, allergies, and gastrointestinal discomforts during practice and after the performance due to the intense exercise, travel, insufficient rest and restricted food consumption. Probiotics are well known as complementary therapeutic and health supplements for several diseases and disorders. Studies suggest that the intervention of probiotics improved the health status of elite athletes, but the results are not consistent in all the studies. The beneficial effect of probiotic supplementation profoundly relies on species or strain, dose, duration, form, and host physiology. The manuscript summarizes the effect of probiotic supplementation on health status of athletes. The literature was collected from PubMed, Scopus, Web of Science, and Google Scholar using the search term “probiotic and athletes”. As per the literature survey, probiotic supplementation improved the intestinal permeability, immune system, intestinal microbiota, inflammatory system, reduced the severity and incidence of respiratory tract infections, and duration of gastrointestinal symptoms. Several studies were conducted on Lactobacillus species and the outcomes were found to be species- or strain-specific. More studies are required to know the detailed mechanism behind the beneficial effect of probiotic intervention in athletes. Further studies are desired on formulation and optimization of probiotic supplements to develop generalized and personalized sports supplements to boost the overall health and enactment of elite athletes.