Do Probiotics Prevent Upper Respiratory Tract Infections?

Do Probiotics Prevent Upper Respiratory Tract Infections?

As a former competitive athlete (in the sports of cycling and winter biathlon), I know that there’s nothing more frustrating than an interruption in your off-season training schedule from getting sick.  With all of the buzz surrounding probiotics, do they actually work to prevent upper respiratory tract infections in athletes (URTI’s)?

To answer that question, let’s take a look at a fairly recent study published in the International Journal of Sports Nutrition and Exercise Metabolism [1].  In this study, researchers from the UK sought to examine the effects of supplementation with probiotics in endurance training athletes during the winter months.

Participants in this study included both men and women (18-55 years old), 84 in total, who were randomized to receive either placebo or a probiotic supplement for 16 weeks.  Specifically, the probiotic group consumed a 65 ml probiotic beverage that contained 6.5 x 109 cells of Lactobacillus casei Shirota.  They consumed this drink twice per day—once at breakfast and again during their evening meal.

Of note, the study participants were not allowed to continue taking other supplements, vitamins, probiotics, or any fermented dairy products during the study.  However, they were asked to continue with their normal training regimes.

What did the researchers find?

  • The proportion of subjects in the placebo group who experienced one or more weeks of URTI symptoms was higher (placebo 0.9, probiotic 0.6, p=0.021)
  • The proportion of weeks that subjects suffered from URTI symptoms was significantly higher in the placebo group compared to the probiotic group (0.23 and 0.12 respectively, p<0.001)
  • The proportion of weeks that subjects took medication was also higher in the placebo group (0.17 and 0.10 respectively, p<0.01)
  • Lastly, the mean number of URTI-symptom weeks (placebo 3.5 +/- 2, probiotic 1.2 +/- 1; P<0.01) and mean number of URTI episodes (placebo 2.1 +/- 1.2, probiotic 1.2 +/-1; p<0.01) were ~50% lower on probiotic than placebo.

Severity and duration of URTI symptoms?

  • When a URTI was present, there were no differences between the placebo and probiotic groups with respect to the mean duration or severity of symptoms.
  • However, the proportion of subjects whose training was interrupted was lower in the probiotic group than placebo (0.54 and 0.81 respectively, p=0.36)


The study authors concluded:

The main findings of the current study were that the proportion of subjects who experienced 1 or more weeks with URTI symptoms was 27% lower and the average number of URTI episodes was 50% lower in the probiotic group than in the placebo group. The severity and duration of symptoms were not significantly different on probiotic than with placebo, but training was less affected when URTI was present for the probiotic group than the placebo group. These positive clinical consequences provide evidence for the beneficial effects of daily LcS (Lactobacillus casei Shirota) ingestion in a cohort of highly physically active people.

How does LcS improve immune function?

In this particular study, the researchers did not find that supplementation with LcS had any substantial effect on modulating circulating levels of leukocyte, neutrophil, lymphocyte, monocyte, or lymphocyte subset numbers.  However, they did not that falls in saliva IgA concentration are associated with infection incidence.  Supplementation with the probiotic used in this study attentuated the decline in salivary IgA concentration compared to placebo.

For more info, see my previous post on natural remedies for the common cold.


  1. Gleeson M, Bishop NC, Oliveira M, Tauler P. Daily probiotic’s (Lactobacillus casei Shirota) reduction of infection incidence in athletes. Int J Sport Nutr Exerc Metab. 2011 Feb;21(1):55-64.
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