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Probiotic supplementation reduces the duration and incidence of infections but not severity in elite rugby union players

Published:September 16, 2013DOI:https://doi.org/10.1016/j.jsams.2013.08.004

      Abstract

      Objectives

      The attenuation of the number and severity of infections is of importance to athletes. Probiotics use has increased over recent years with beneficial effects believed to include improvements in immune function. Research has focused on their effectiveness for reducing the number, duration and severity of infections amongst endurance athletes. At present no research has been undertaken with team sport athletes. This randomised controlled trial aimed to determine the effectiveness of probiotics on the number, duration and severity of infections amongst elite union rugby players.

      Design

      Randomised control trial with two arms; placebo and probiotic.

      Methods

      Thirty elite rugby union players were allocated in random order to receive a probiotics supplement or a placebo for four weeks each. Supplements were consumed on a daily basis. There was a four week washout period between treatments. Participants completed a daily diary to identify and rate the severity of any infectious symptoms.

      Results

      During the probiotic treatment 14/30 participants never experienced a single upper respiratory tract illness (URTI) or gastrointestinal (GI) episode, compared to 6/30 on the placebo supplementation (p = 0.033). The mean ± standard deviation for the number of days of illness tended to be higher for the placebo, (5.8 ± 6.6 days) than probiotic (3.4 ± 4.6 days), (p = 0.054). There was no significant difference in the severity of the symptoms between the two treatment groups (p = 0.110).

      Conclusions

      These positive effects of probiotic supplements provide evidence for the beneficial effects of daily supplementation with these probiotic strains in highly trained rugby union players.

      Keywords

      1. Introduction

      Athletes engaging in prolonged intense exercise may be more susceptible to upper respiratory tract illness (URTI), than individuals participating in moderate or no exercise.
      • Nieman D.C.
      Exercise, upper respiratory tract infection, and the immune system.
      • Reid V.L.
      • Gleeson M.
      • Williams N.
      • et al.
      Clinical investigation of athletes with persistent fatigue and/or recurrent infections.
      Attenuating the risk of infection is of interest to coaches and sports physicians, as illness can result in impaired performance or missed training days. Elite rugby union players can train for approximately four to five hours a day 5–6 days a week with competitive matches once a week. This intensive training schedule may put these players at increased risk of URTI and suppressed immune function whilst at the same time increasing exposure to pathogens.
      • Nieman D.C.
      Marathon training and immune function.
      • Gleeson M.
      • Nieman D.C.
      • Pedersen B.K.
      Exercise, nutrition and immune function.
      • Brolinson P.G.
      • Elliott D.
      Exercise and the immune system.
      In team sports settings, where athletes are competing on a regular basis in such close proximity, sharing bottles and shaking hands, the risk viruses will be passed on to other members of the squad is increased.
      • Cunniffe B.
      • Griffiths H.
      • Proctor W.
      • et al.
      Mucosal immunity and illness incidence in elite rugby union players across a season.
      This is especially true in contact sports.
      One emerging supplement that may attenuate the risk of some infections are probiotics. These supplements alter gut microflora, which may stimulate immune function and have been associated with numerous health claims; the majority of which have focused on their beneficial effects on the immune system and/or the gastrointestinal tract. The benefits from probiotic supplementation is believed to be strain specific, as only a few strains have been found to survive gastric transit and can persist in the intestinal lumen.
      • Nichols A.W.
      Probiotics and athletic performance: a systematic review.
      • Gleeson M.
      • Bishop N.C.
      • Oliveira M.
      • et al.
      Daily probiotic's (Lactobacillus casei Shirota) reduction of infection incidence in athletes.
      Therefore, the most common strains used to promote immune function are lactic acid bacteria (LAB); Lactobacillus and Bifidobacterium species.
      A handful of studies have been published which investigate the effects of probiotic supplementation and immune function amongst athletes.
      • Gleeson M.
      • Bishop N.C.
      • Oliveira M.
      • et al.
      Effects of a Lactobacillus salivarius probiotic intervention on infection, cold symptom duration/severity and mucosal immunity in endurance athletes.
      • West N.P.
      • Pyne D.B.
      • Cripps A.W.
      • et al.
      Lactobacillus fermentum (PCC(R)) supplementation and gastrointestinal and respiratory-tract illness symptoms: a randomised control trial in athletes.
      • Fricker P.A.
      • Pyne D.B.
      • Saunders P.U.
      • et al.
      Influence of training loads on patterns of illness in elite distance runners.
      The predominant population of focus in these studies has been endurance athletes. The duration of the interventions have ranged from three weeks to four months.
      • Gleeson M.
      • Bishop N.C.
      • Oliveira M.
      • et al.
      Effects of a Lactobacillus salivarius probiotic intervention on infection, cold symptom duration/severity and mucosal immunity in endurance athletes.
      • Tiollier E.
      • Chennaoui M.
      • Gomez-Merino D.
      • et al.
      Effect of a probiotics supplementation on respiratory infections and immune and hormonal parameters during intense military training.
      Although the probiotic strains, concentrations and administration methods have varied, they have generally shown beneficial effects.
      Therefore it appears that probiotic supplementation may be beneficial by attenuating illness in endurance athletes. However, to date there is limited evidence to suggest rugby union players will also benefit from probiotic supplementation. Therefore this intervention study aimed to investigate the effect of four weeks probiotic supplementation on the incidence, duration and severity of infections during a month of competitive rugby union. Thus, testing the hypothesis that probiotic supplementation would reduce the number, duration and severity of infection symptoms amongst elite rugby union players.

      2. Methods

      The study was a randomised, single-blind, placebo-controlled, crossover trial with two arms: probiotics and placebo. Each treatment arm lasted four weeks, separated by a 4 week washout period, between the winter months of May to July (temperature range −4 to +18 °C). Probiotics or placebo supplements (independent variables) were consumed on a daily basis and a symptoms diary
      • Gleeson M.
      • Bishop N.C.
      • Oliveira M.
      • et al.
      Daily probiotic's (Lactobacillus casei Shirota) reduction of infection incidence in athletes.
      • Gleeson M.
      • Bishop N.C.
      • Oliveira M.
      • et al.
      Effects of a Lactobacillus salivarius probiotic intervention on infection, cold symptom duration/severity and mucosal immunity in endurance athletes.
      • Tiollier E.
      • Chennaoui M.
      • Gomez-Merino D.
      • et al.
      Effect of a probiotics supplementation on respiratory infections and immune and hormonal parameters during intense military training.
      was completed every day to identify the dependant variables; symptoms of upper respiratory tract, gastrointestinal and other infections. The use of self-reported infections allow for a better understanding of how a player feels and minimises the burden on participants compared to blood samples, which is important in an elite sports setting.
      The University of Otago Human Ethics Committee approved this study, and the measurements were described to all players before they gave their written consent to participate and the study complied with the declaration of Helsinki at all times.
      All participants were elite rugby union players competing in the southern hemisphere's premier rugby union competition. Thirty healthy young (mean ± standard deviation) 24.7 ± 3.6 years old, male rugby union players participated in the study. Mean body mass was 104 ± 12.8 kg (Tanita Personal scale UM-071) on the morning of the first day of the trial before training commenced.
      Throughout the study participants continued with their normal training and competition programme. They were asked to maintain a normal diet, yet were given instruction to refrain from eating probiotic-enriched yoghurt and probiotic and prebiotic enriched foods or supplements (probiotic, vitamins and minerals) during this period.
      During the study participants trained 4 days a week at the training centre (typically around 4 h per day), and participated in 1 day of competition and 2 days of self-regeneration and light training. Training included gym work, weights, skills, and fitness tests. Each week, a team was named for competition. Those not named in the competition team trained at the training centre 5 days a week.
      Participants were provided in random order with either a commercially availiable probiotic gelatine capsule or a placebo capsule containing cornflour. The probiotic capsules containing three acid-resistant strains of bacteria (Lactobacillus gasseri: 2.6 billion colony-forming units (CFUs), Bifidobacterium bifidum: 0.2 billion organisms, Bifidobacterium longum: 0.2 billion organisms) (Probiotica P3, Nutra-life, Auckland, New Zealand). This product was chosen as it contains the lactobacillus strain of probiotics which have previously been shown to be beneficial for athletes
      • Tiollier E.
      • Chennaoui M.
      • Gomez-Merino D.
      • et al.
      Effect of a probiotics supplementation on respiratory infections and immune and hormonal parameters during intense military training.
      and does not need to be refridgerated making it more convenient for use in a team sport setting.
      Participants were required to consume one pill per day throughout the two arms of the trial and at the same time to complete a symptoms diary on infection and severity. To enhance compliance, a researcher attended training sessions each day and provided the participants with their allocated capsule in a named container. At this time the participants also completed a daily symptoms questionnaire.
      • Gleeson M.
      • Bishop N.C.
      • Oliveira M.
      • et al.
      Effects of a Lactobacillus salivarius probiotic intervention on infection, cold symptom duration/severity and mucosal immunity in endurance athletes.
      • Tiollier E.
      • Chennaoui M.
      • Gomez-Merino D.
      • et al.
      Effect of a probiotics supplementation on respiratory infections and immune and hormonal parameters during intense military training.
      • West N.P.
      • Pyne D.B.
      • Cripps A.W.
      • et al.
      Lactobacillus fermentum (PCC(R)) supplementation and gastrointestinal and respiratory-tract illness symptoms: a randomised control trial in athletes.
      On the days that participants were not training, participants were given a pack of capsules to take away with them and were sent a reminder via SMS to take their capsule each morning. For the non-training days, a compliance log of supplement use was recorded and participants were asked to report if they had missed any days of supplementation. Participants were also required to continue to complete daily symptoms questionnaires and bring them to the next session. If symptoms forms were not returned the participants were asked to report any symptoms of illness and fill in another form. Participants were required to report any medications they were taking during the intervention period (e.g. pain killers) however; they were not required to abstain from any medications if they were suffering from illness symptoms. At the end of each intervention period the participants were asked to identify which treatment they thought they had just completed.
      The symptoms questionnaire has previously been described
      • Gleeson M.
      • Bishop N.C.
      • Oliveira M.
      • et al.
      Effects of a Lactobacillus salivarius probiotic intervention on infection, cold symptom duration/severity and mucosal immunity in endurance athletes.
      • Tiollier E.
      • Chennaoui M.
      • Gomez-Merino D.
      • et al.
      Effect of a probiotics supplementation on respiratory infections and immune and hormonal parameters during intense military training.
      • Cox A.J.
      • Pyne D.B.
      • Saunders P.U.
      • et al.
      Oral administration of the probiotic Lactobacillus fermentum VRI-003 and mucosal immunity in endurance athletes.
      and covered the following types of infection: upper respiratory tract and chest infections, influenza, gastrointestinal distress, headache, eye irritation, rashes, skin abscesses and other. The severity of the symptoms were self-rated as mild, moderate and severe based on the impact of the illness symptoms on the subject's training volume and intensity for the day. Mild, resume normal training; moderate, normal/altered training; severe, altered/no training. Injuries were considered when symptoms were recorded, for example, with headaches it was questioned whether it was due to training/competition injury (concussion) or illness related. The incidence score relates to the number of participants who reported that symptom during each arm of the study. One or more symptoms on at least two consecutive days were defined as an episode of illness. Symptoms only separated by one day were counted as the same episode.
      In order to detect a 30% reduction in the number of infected days with 80% power and type 1 error of 5% a total of 25 participants were required. Accounting for dropouts, 34 participants were recruited at baseline.
      • Gleeson M.
      • Bishop N.C.
      • Oliveira M.
      • et al.
      Daily probiotic's (Lactobacillus casei Shirota) reduction of infection incidence in athletes.
      All analyses were conducted using STATA version 12 (STATA Corporation, College Station, TX, USA) with statistical significance set at P ≤ 0.05. The incidence of symptoms were compared between the two treatments using McNemar's test for presence/absence of symptoms. The Wilcoxon's matched-pairs signed ranks test was used to compare the severity of symptoms, the number of episodes of illness, and the length of episodes of illness between treatments. Compliance to the two treatments was compared using a paired t-test.
      A total severity score was calculated by summing all of the severity scores for all symptoms over the 28 day intervention. A total illness score was calculated by multiplying the total severity score by the number of days of illness. The Wilcoxon's matched-pairs signed ranks test was used to compare the total severity score and the total illness score between treatments. Data are presented as mean ± standard deviation unless otherwise stated.

      3. Results

      Adherence to the study was good, the mean number of days missed per participant during the probiotic trial was 3.7 days (range 1–9 days) and during the placebo trial was 4.4 days (range 1–14 days) which was not significantly different between the trials, p = 0.233.
      Upon completion of the study, participants were asked to identify which treatment they thought they had just completed. Seventy percent reported they did not know, 13% thought they were on the probiotic, and 17% thought they were on the placebo. Of the participants who answered they thought they were on either the probiotic or placebo, 44% were correct and 56% were incorrect. Thus blinding appeared to be effective.
      There were no substantial differences between the treatments in terms of the mean amount of competitive matches played by participants in each intervention which equated to 2.9 and 3.9 games out of a possible 6 games for probiotic and placebo respectively.
      There was no significant difference in the reported incidence of URTI symptoms between the two treatments, with 19 players reporting an incidence for the placebo and 16 on the probiotic (p = 0.366) (Table 1). However, the number of players who reported an incidence for any symptom was significantly higher on the placebo (24) compared to the probiotic (16) supplementation (p = 0.033).
      Table 1Number of players reporting an incidence of symptoms on the Probiotic and Placebo supplementation.
      SymptomProbioticPlacebo
      nProportionnProportionDifference (95% CI)OR (95% CI)p-value
      URTI:

      sneezing, stuffy/runny nose, sore throat
      160.53190.63−0.10 (−0.35–0.15)0.57 (0.12–2.25)0.366
      Chest infection:

      cough, sputum, congestion
      100.33100.330.00 (−0.21–0.22)1.00 (0.19–5.37)1.000
      Flu:

      aching joints, fever, chills
      50.1770.23−0.07 (−0.23–0.01)0.33 (0.01–4.15)0.317
      GI distress:

      nausea, vomiting, diarrhoea
      40.1350.130.00 (−0.16–0.16)1.00 (0.07–13.80)1.000
      Headache:70.2360.200 .03 (−0.20–0.26)1.25 (0.27–6.30)0.739
      Eye irritation:

      Itchy, red, watery
      30.1040.100.00 (−0.16–0.16)1.00 (0.07–13.80)1.000
      Rashes:

      spots, measles
      10.0300.000.03 (−0.06–0.13)0.00 (0.00–39.00)0.317
      Skin abscesses:

      boils, skin infections
      00.0010.03−0.03 (−0.13–0.06)0.00 (0.03–39.00)0.317
      Other:00.0000.000.00 (−0.03–0.03)0.317
      Any symptom160.53240.80−0.26 (−0.53–0.01)0.27 (0.05–1.03)0.033
      Analysis of the symptoms questionnaires indicated 14 participants did not experience a single URTI or GI episode during the probiotic intervention, compared to only 6 on the placebo supplementation (p = 0.033). One person on the placebo reported more than 4 episodes of illness. However, the mean ± SD duration of each episode of URTI was not statistically different on the probiotic compared to the placebo (4.8 ± 2.9 days vs. 6.7 ± 7.9 days, p = 0.119). Neither was the mean duration of the episodes for all symptoms (4.6 ± 3.1 days vs. 7.2 ± 6.9 days, p = 0.505).
      The mean ± standard deviation for the number of days of illness tended to be higher for the placebo (5.8 ± 6.6 days), than for the probiotic (3.4 ± 4.6 days), (p = 0.054).
      There was no significant difference in the severity of the symptoms between the two treatment groups. The mean ± standard deviation for the summed severity score for all symptoms was 8.77 ± 25.1 for participants on the probiotic and 13.33 ± 14.6 (p = 0.110) for the placebo.

      4. Discussion

      The most important finding of the present study was a significant reduction in the number of URTI or GI episodes in participants on the probiotic intervention (containing three strains of bacteria; Lactobacillus gasseri, Bifidobacterium bifidum, Bifidobacterium longum) compared to the placebo. A significant reduction in the number of days reporting any symptoms during the probiotic treatment compared with a placebo, indicates positive clinical consequences and provides evidence for the beneficial effects of daily supplementation with these probiotic strains in highly trained rugby union players.
      Unlike other studies where the intensity, duration and the physiological demands of training and competition have varied, the participants in the present study participants completed the same training. Further differentiating this study from other published research is the type of training undertaken in the present study which consisted of repeated brief high-intensity efforts with short rest intervals involving heavy physical contact, intense gym sessions, weights, skills and fitness tests which compares to the lower intensity endurance exercise of most participants in previous research.
      • Gleeson M.
      • Bishop N.C.
      • Oliveira M.
      • et al.
      Effects of a Lactobacillus salivarius probiotic intervention on infection, cold symptom duration/severity and mucosal immunity in endurance athletes.
      • Tiollier E.
      • Chennaoui M.
      • Gomez-Merino D.
      • et al.
      Effect of a probiotics supplementation on respiratory infections and immune and hormonal parameters during intense military training.
      • West N.P.
      • Pyne D.B.
      • Cripps A.W.
      • et al.
      Lactobacillus fermentum (PCC(R)) supplementation and gastrointestinal and respiratory-tract illness symptoms: a randomised control trial in athletes.
      The present study corroborates with two recent studies suggesting probiotics reduce illness incidence in athletes.
      • Gleeson M.
      • Bishop N.C.
      • Oliveira M.
      • et al.
      Daily probiotic's (Lactobacillus casei Shirota) reduction of infection incidence in athletes.
      • Cox A.J.
      • Pyne D.B.
      • Saunders P.U.
      • et al.
      Oral administration of the probiotic Lactobacillus fermentum VRI-003 and mucosal immunity in endurance athletes.
      Indeed the design of the present study is similar to the study by Cox et al.,
      • Cox A.J.
      • Pyne D.B.
      • Saunders P.U.
      • et al.
      Oral administration of the probiotic Lactobacillus fermentum VRI-003 and mucosal immunity in endurance athletes.
      with both reporting beneficial effects. However, not all studies have reported a reduction in the illness incidence with probiotic supplementation.
      • Gleeson M.
      • Bishop N.C.
      • Oliveira M.
      • et al.
      Effects of a Lactobacillus salivarius probiotic intervention on infection, cold symptom duration/severity and mucosal immunity in endurance athletes.
      • Kekkonen R.A.
      • Vasankari T.J.
      • Vuorimaa T.
      • et al.
      The effect of probiotics on respiratory infections and gastrointestinal symptoms during training in marathon runners.
      Protocol differences including the length of probiotic supplementation and probiotic strain may account for these differences. Studies which found no benefits in illness incidence
      • Tiollier E.
      • Chennaoui M.
      • Gomez-Merino D.
      • et al.
      Effect of a probiotics supplementation on respiratory infections and immune and hormonal parameters during intense military training.
      • Kekkonen R.A.
      • Vasankari T.J.
      • Vuorimaa T.
      • et al.
      The effect of probiotics on respiratory infections and gastrointestinal symptoms during training in marathon runners.
      used L. salvarius and L. rhamnosus GG whereas Lactobacillus gasseri, Bifidobacterium bifidum, and Bifidobacterium longum were used in the present study. Indeed a longer intervention period for the present study may have resulted in a greater number of illness symptoms and may have provided a clearer picture of the effects of probiotic supplementation.
      The present study was conducted in a contact team environment, involving male players who, shake others hands and are consistently in close physical contact with one and other, overall increasing the susceptibility of illness especially URTI. If one team member becomes ill, it can easily spread throughout the entire squad. This may account for the large proportion of participants who reported an incidence of illness in the present study. Previous studies which failed to find a reduction in illness incidence
      • Gleeson M.
      • Bishop N.C.
      • Oliveira M.
      • et al.
      Effects of a Lactobacillus salivarius probiotic intervention on infection, cold symptom duration/severity and mucosal immunity in endurance athletes.
      • West N.P.
      • Pyne D.B.
      • Cripps A.W.
      • et al.
      Lactobacillus fermentum (PCC(R)) supplementation and gastrointestinal and respiratory-tract illness symptoms: a randomised control trial in athletes.
      • Kekkonen R.A.
      • Vasankari T.J.
      • Vuorimaa T.
      • et al.
      The effect of probiotics on respiratory infections and gastrointestinal symptoms during training in marathon runners.
      may not have had a large number of illness incidence reported, as these studies were predominately focused on athletes partaking in individualised sports.
      The beneficial effects of probiotic administration on the incidence of any symptom are possibly linked to stimulation of the immune cells thereby increasing immunity.
      • Ha S.
      Probiotics from an immunological point of view.
      However, the present study did not have a means to determine these through immune parameters such as IFNγ and whole-blood cytokine concentrations, due to constraints of working with elite athletes. However, the evident reduction in illness incidence found in the present study suggests probiotics may be a useful nutrition supplement for elite rugby union players during the season. Probiotics can provide an improvement in resistance to common illness resulting in less training and competition missed/impaired by illness, overall enhancing athletic performance.
      The present study used a daily symptoms questionnaire in line with a number of previous studies
      • Tiollier E.
      • Chennaoui M.
      • Gomez-Merino D.
      • et al.
      Effect of a probiotics supplementation on respiratory infections and immune and hormonal parameters during intense military training.
      • Cox A.J.
      • Pyne D.B.
      • Saunders P.U.
      • et al.
      Oral administration of the probiotic Lactobacillus fermentum VRI-003 and mucosal immunity in endurance athletes.
      • Kekkonen R.A.
      • Vasankari T.J.
      • Vuorimaa T.
      • et al.
      The effect of probiotics on respiratory infections and gastrointestinal symptoms during training in marathon runners.
      whereas both the Gleeson studies
      • Gleeson M.
      • Bishop N.C.
      • Oliveira M.
      • et al.
      Daily probiotic's (Lactobacillus casei Shirota) reduction of infection incidence in athletes.
      • Gleeson M.
      • Bishop N.C.
      • Oliveira M.
      • et al.
      Effects of a Lactobacillus salivarius probiotic intervention on infection, cold symptom duration/severity and mucosal immunity in endurance athletes.
      required participants to complete a weekly questionnaire. Our study is the first to date that has had a researcher present to record daily compliance for supplement consumption as well as monitoring the completion of the symptoms questionnaires. This method probably enhanced compliance as well as accuracy of completing the questionnaires. Previous studies have shown that when using such a questionnaire, 79% of reported symptoms were classed as upper respiratory tract illness by a physician with the remainder being classed as influenza or allergies.
      • Fricker P.A.
      • Pyne D.B.
      • Saunders P.U.
      • et al.
      Influence of training loads on patterns of illness in elite distance runners.
      However, the use of measuring reported symptoms rather than measuring markers of immune function has its limitations. It is possible for athletes to report an illness symptom which may not be related to an infection. Therefore the number of infections maybe overestimated by this method.
      The severity of symptoms in the present study were self-rated as mild, moderate or severe based on the impact of the symptoms on training for that day and were recorded on daily symptoms questionnaires. Mild symptoms, having no affect on training, moderate were defined as necessitating a reduction in training volume/intensity, and severe symptoms were defined as total cessation of training on that day. This self-reported method has been implemented in previous studies to measure symptoms severity.
      • Gleeson M.
      • Bishop N.C.
      • Oliveira M.
      • et al.
      Daily probiotic's (Lactobacillus casei Shirota) reduction of infection incidence in athletes.
      • Gleeson M.
      • Bishop N.C.
      • Oliveira M.
      • et al.
      Effects of a Lactobacillus salivarius probiotic intervention on infection, cold symptom duration/severity and mucosal immunity in endurance athletes.
      • West N.P.
      • Pyne D.B.
      • Cripps A.W.
      • et al.
      Lactobacillus fermentum (PCC(R)) supplementation and gastrointestinal and respiratory-tract illness symptoms: a randomised control trial in athletes.
      The present study did not find probiotics to have any significant effect on the severity of either URTI or GI symptoms in elite rugby union players. However, other studies have found probiotic supplementation decreases the severity of symptoms in the general population
      • de Vrese M.
      • Winkler P.
      • Rautenberg P.
      • et al.
      Probiotic bacteria reduced duration and severity but not the incidence of common cold episodes in a double blind, randomized, controlled trial.
      • Pregliasco F.
      • Anselmi G.
      • Fonte L.
      • et al.
      A new chance of preventing winter diseases by the administration of synbiotic formulations.
      as well as in male endurance athletes.
      • West N.P.
      • Pyne D.B.
      • Cripps A.W.
      • et al.
      Lactobacillus fermentum (PCC(R)) supplementation and gastrointestinal and respiratory-tract illness symptoms: a randomised control trial in athletes.
      • Cox A.J.
      • Pyne D.B.
      • Saunders P.U.
      • et al.
      Oral administration of the probiotic Lactobacillus fermentum VRI-003 and mucosal immunity in endurance athletes.
      Throughout the intervention periods during the present study it become apparent the participants rarely reported a symptom as severe enough to discontinue training. This was possibly because these elite rugby union players were required to attempt training when ill unless completely absent from the training site for that day. Therefore these data may have lacked the sensitivity to detect any differences. Further medications to alleviate the symptoms of any illness were permitted during the study, this may have influenced both the severity and duration of any illness during the study.
      Another limitation associated with the present study was that during the bye weeks in week three of both intervention periods, the participants did not attend the training centre for five consecutive days. The participants were provided with pills and symptoms questionnaires for the five days they were away. During this period compliance cannot be confirmed as the researcher was not present to observe this. The participants were sent a SMS daily as a reminder and were asked about compliance when they returned to the training centre to receive their intervention. However, previous research has not provided daily supplementation and therefore it is likely that the supplementation protocol was more closely followed in the present study.

      5. Conclusion

      The present study supports the hypothesis that probiotic supplementation will reduce the duration of ilness symptoms amongst elite rugby union players. It demonstrates probiotic supplementation ingested on a daily basis at a dose rate of 3.0 × 109 cfu reduces the number of participants who report any incidence of an infectious symptom in highly trained elite rugby union players. These findings constitute an important benefit to rugby union players partaking in intense training and competition schedules. Episodes of illness often occur during heavy exercise training periods, and it interrupts training sessions and can hinder performance during competition. The demand for players to perform on a daily basis is high as selection for starting squads for competition are based on training performance. Thus it is important for rugby union players to find practical ways to enhance their immune system to avoid performance impairment as a result of illness.

      Practical implications

      • The probiotics used in this study may be a nutritional supplement that can prevent and/or decrease the number of days of illness in elite rugby union players.
      • Performance was not measured in this study and therefore conclusions on limiting the number of days of illness on performance benefits cannot be stated, this should be investigated in future studies.
      • The cost of probiotics is relatively expensive in comparison to other measures that can be taken to reduce the spread of infection, for example proper hygiene, not sharing bottles and the influenza vaccination.
      • For the benefits to become evident it would require each player from the squad to take one capsule per day, therefore player motivation would need to be high in order for adequate compliance to occur.

      Acknowledgments

      The authors would like to thank the players and coaching staff who assisted with this study. This study was funded by the Department of Human Nutrition, University of Otago and there are no conflicts of interest.

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