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Daily consumption of Lactobacillus casei strain Shirota (LcS) reduces the incidence of upper respiratory tract infections, drinking Yakult daily Yakult trial at Loughborough University, UK

January 2011

Results of a recent trial by Professor Michael Gleeson (Loughborough University, UK) have been announced, which demonstrated a clear health benefit for athletes drinking the commercially available fermented milk drink Yakult, which contains the unique probiotic strain LcS. The athletes were staff and students at the university who were involved in regular intensive sports training, such as cycling, triathlon, middle-long distance running or swimming.

The results confirmed that daily consumption of Yakult was effective in reducing the incidence of common colds (i.e. upper respiratory tract infections, URTIs) in the athletes. In an earlier research it has been demonstrated that as a group, athletes are susceptible to infections due to a depression of their immune system.

The study was fully described and published online in the scientific peer-reviewed journal International Journal of Sport Nutrition & Exercise Metabolism .



The double-blind trial was conducted in 84 endurance athletes. Subjects were divided into 2 groups: 42 received Yakult (6.5 x 109 live cells of a probiotic strain LcS in each bottle) and 42 received a placebo. After subjects consumed the given drink twice daily for 16 weeks, the drinking effect on incidence of URTI and immune parameters was examined.

The summary of the results is as follows:

  1. Incidence of URTI (generally known as common cold)
    The proportion of subjects from the Yakult group who experienced one or more weeks with URTI symptoms was 66%, which was significantly lower than that from the placebo group (90%). 
  2. Saliva IgA concentration1 , which can be lowered by prolonged hard sports, was higher in the Yakult group than in the placebo group.
  3. Discussion
    Based on these findings, the researchers conclude that daily consumption of fermented milk drink containing LcS lowers the incidence of URTI in athletes who are engaged in prolonged hard sports. The amount of sIgA antibodies was kept in an optimal condition, which can be considered as one of the factors for the effect.

*The placebo drink did not contain LcS. The taste and color of both the placebo drink and “Yakult” were similar. By comparing the effects of intake of each drink, the efficacy of “Yakult” can be scientifically measured.

1 sIgA is an antibody contained in saliva and airway mucus, and plays a critical role to prevent virus infection.


[Comment from Prof. Michael Gleeson of Loughborough University]

Prof Michael Gleeson (Professor of Exercise Biochemistry in the School of Sport, Exercise and Health Sciences) who led the study at Loughborough University commented: “There is relatively little evidence for the effectiveness of so-called dietary immunostimulants in the athletic population but this study suggests that a probiotic product may help to reduce the risk of infection. Athletes hate the thought of picking up colds as even minor ailments can impair their training and performance or even stop them from competing.” 


[Comment from Dr. Haruji Sawada, Ph.D., the director of the Yakult Central Institute for Microbiological
 Research (YCIMR)]

Yakult Honsha Co., Ltd. participated in this study as sponsor by providing funding and test samples.
Dr. Haruji Sawada of the YCIMR commented: “It is a valuable result that the daily consumption of our product, Yakult, is proven to contribute to the maintenance of a good state of upper respiratory tract in healthy sports persons. This study has resulted in important data that are further evidence of immune benefits associated with drinking Yakult.” 


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