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Gleeson et al (2011) Daily probiotic’s (Lactobacillus casei Shirota) reduction of infection incidence in athletes

Gleeson et al (2011) Daily probiotic’s (Lactobacillus casei Shirota) reduction of infection incidence in athletes


Gleeson M, Bishop NC, Oliveira M, Tauler P (2011) Daily probiotic’s (Lactobacillus casei Shirota) reduction of infection incidence in athletes. International Journal of Sport Nutrition & Exercise Metabolism 21:55-64


To investigate the effect of the probiotic Lactobacillus casei Shirota (LcS) on immune markers and incidence of upper respiratory tract infections (URTI), in sports people during four months of endurance-based sports activities in winter. 


The double-blind, placebo-controlled study conducted at Loughborough University, randomised 84 healthy adults engaged in regular sports training (mainly running, cycling, swimming, triathlons, team games and racquet sports) to take a probiotic (LcS) or placebo for 16 weeks. At baseline, 8 and 16 weeks, resting blood and saliva samples were taken and tested for a broad range of immune parameters: immunoglobulins, cell counts and cytokines. The subjects also kept weekly records of their training and any illness. Subjects were required to maintain a minimum level of training.


Analysis of the subjects who completed the full 16 weeks of the study (n = 58), showed that the proportion of those who had one or more weeks of URTI symptoms was 27% lower in the probiotic group compared to placebo (P = 0.021). The average number of URTI episodes was also 50% lower in the probiotic group compared to placebo (P P

The main finding from the analysis of immune parameters, was that after 8 and 16 weeks of intervention, salivary IgA concentrations were higher in the probiotic group compared to the placebo group (P = 0.03).

The probiotic group also experienced significantly fewer days with GI discomfort symptoms (P = 0.008).

Subject dropout was mainly due to air travel to competitions, injury or persistent illness. These prevented the subjects either being able to take the drinks or undertake the minimum level of training required for the study. Blinding was shown to be effective.

Table 1: Data showing beneficial effects of 16 weeks intervention with the probiotic L. casei Shirota in athletes during a period of intense physical training on URTI.


Probiotic (LcS) group

Placebo group


Proportion of subjects with ≥ 1 week URTI symptoms



P = 0.021

Mean number of URTI episodes

1.2 ± 1.0

2.1 ± 1.2

P < 0.01

Mean number of URTI symptom weeks

1.9 ± 1.5

3.5 ± 2.0

P < 0.01

Proportion of weeks with URTI episodes



P < 0.001

Proportion of weeks that medication was taken



P < 0.01

Proportion of subjects whose training was impaired during URTI symptoms



P < 0.036

Proportion of days with GI discomfort symptoms



P < 0.008


The authors concluded that regular ingestion of the probiotic (LcS) appeared to be beneficial in reducing the frequency of URTI in this group of athletes.

The data indicated that this benefit might be related to better maintenance of salivary IgA in the athletes taking the probiotic, reducing the negative effects of regular intense sports training during winter. 

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