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Probiotic supplements, the immune system and athletes: What do we know?

March 20, 2019

As mentioned in my review of Yakult (find it here), a probiotic is defined by the World Health Organisation (WHO) as: ‘live microorganisms which when administered in adequate amounts confer a health benefit on the host’.

Probiotics are found in some fermented dairy foods and nutritional supplements.

Literature regarding the effect of probiotics on athletes has lagged behind both animal studies and studies focussed on clinical conditions in the general population (Pyne et al, 2014.)

So why study the effect of probiotics on athletes?

Athletes can have a higher risk of recurrent upper respiratory tract infections (URTI’s) compared to the general population (Reid et al, 2004). URTI’s can cause athletes to miss training and competition. Therefore, anything we can do to reduce the incidence of URTI’s seems a worthy pursuit.

Why are athletes at higher risk of URTI’s?

A great review article by Nieman (1994) presents both epidemiological and clinical data to support the concept that heavy exertionincreases an athlete’s risk of upper respiratory tract infections because of negative changes in immune function and elevation of the stress hormones, epinephrine and cortisol. The same does not seem to hold true for moderate forms of exercise.

My summary of some of the literature:

Rugby Union players:

Haywood et al (2014) investigated the effect of four weeks of probiotic supplementation on the incidence, duration and severity of infections in 30 elite rugby union players during a month of competitive rugby union.

The participants trained four days per week (~4hr per day) and participated in one day of competition and two days of self-regeneration and light training. They were asked to maintain a normal diet but to exclude probiotic-enriched yoghurt and probiotic and prebiotic enriched foods or supplements.

The study was a randomised, single-blind, placebo-controlled crossover trial. The participants were given a daily probiotic capsule containing three acid-resistant strains of bacteria (Lactobacillus gasseri: 2.6 billion colony-forming units (CFUs), Bifidobacterium bificum: 0.2 billion organisms, Bifidobacterium longum:0.2 billion organisms) (Probiotics P3, Nutra-life), or a placebo. A daily symptoms questionnaire was kept by each player.

This study showed that daily probiotic use can reduce the incidence of illness and duration of illness symptoms in elite rugby union players.

Endurance based athletes:

Study 1: This study was a randomised, cross-over and double-blind trial. 54 male and female highly active athletes took either a placebo or Lactobacillus salivarius(2 x 1010bacterium CFU’s) for 16 weeks in spring. Nil differences in incidence or severity of URTI symptoms were found between the groups.

Markers of immune function (blood leukocyte, neutrophil, monocyte, and lymphocyte counts; saliva IgA; and lysozyme concentrations) did not change over the course of the study on probiotic compared with placebo. (Gleeson et al, 2012.)

Study 2: This study was a randomized, double-blind and placebo-controlled trial. 58 highly active male and female subjects took either a placebo or Lactobacillus casei Shirotafor 16 weeks in winter.

The probiotic appeared to be beneficial in reducing the frequency of upper respiratory tract infections. The proportion of subjects on the placebo who experienced one or more weeks with URTI symtoms was 36% higher than the probioitic. Severity and duration was not significantly different between the groups (Gleeson et al, 2011.)

Cyclists and triathletes:

This was a randomised, double-blind and placebo-controlled parallel group design study. 88 cyclists and triathletes took either a placebo or a minimum of 1 billion colony-forming units of Lactobacillus fermentumover a 15-week winter training period. They found supplementation with Lactobacillus fermentum was associated with a reduction of symptoms in clinical indices of lower respiratory illness, gastro intestinal symptoms at high training loads, and cold and flu medication use in well-trained male cyclists. Some females had an increase in symptoms. There was no effect of probiotic supplementation on upper respiratory tract infections (West et al, 2011.)


Study 1: This was a randomised, double-blind, placebo-controlled intervention study. 141 male marathon runners took either a placebo or Lactobacillus rhamnosus over a three month summer training period. There was no effect on incidence of respiratory infections (Kekkonen et al, 2007.)

Study 2: This was a double-blind, placebo-controlled, crossover trial involving 20 elite male distance runners. They took either a placebo or Lactobacillus fermentum (1.26 x 1010 ) over four months in winter.

The runners reported less than half the number of days of respiratory symptom during probiotic use compared to placebo. Illness severity was also lower for episodes during probioitic use (Cox et al, 2010.)


This was a randomised, double-blind, placebo controlled study involving 17 female Division I swimmers. They took Bifidobacterium longum (1 x 109) or a placebo for six weeks of off season training. The authors found no effect of the probiotic on immune function (Carbuhn et al, 2018.)

What do the 7 studies I reviewed suggest?

The 7 studies I reviewed tend to suggest that probiotic use may reduce either the frequency, severity and/or duration of upper respiratory tract infections. However, conclusive and specific data about:
– WHO probiotics might benefit, as well as
– which TYPE of probiotic is most effective, as well as
– what DOSAGE is most effective, as well as for
– HOW LONG one needs to take a probiotic for optimum benefit,

… still lacking.

The above studies show that there may be differences between men and women, differences in the effectiveness of various strains and concentration of strains and potential differences in the time-frame needed to be on the probiotic for best effect.

What else should an athlete consider when it comes to immune function?

Well, let’s not forget that other factors (besides heavy exertion) affect the immune system: nutrition, sleep and stress. Nieman (1994) suggests that ‘athletes are urged to eat a well-balanced diet, keep other life stresses to a minimum, avoid overtraining and chronic fatigue, obtain adequate sleep, and space vigorous workouts and race events as far apart as possible.’



**All supplements come with risks. Speak to your Accredited Sports Dietitian before using any kind of supplement.**


Carbuhn, A. F., Reynolds, S. M., Campbell, C. W., Bradford, L. A., Deckert, J. A., Kreutzer, A. & Fry, A. C. (2018). Effects of probiotic (Biffidobacterium longum 35624) supplementation on exercise performance, immune modulation, and cognitive outlook in division I female swimmers, Sports, 6(4): 116.
Cox, A. J., Pyne, D. B., Saunders, P. U. & Fricker, P. A. (2011). Oral administration of the probiotic Lactobacillus fermentum VRI-003 and mucosal immunity in endurance athletes, British Journal of Sports Medicine, 44(4): 222-226.
Gleeson, M., Bishop, N. C., Oliverira, M., Tauler, P. (2011). Daily probiotic’s (Lactobacillus casei Shirota) reduction of infection incidence in athletes, International Journal of Sport Nutrition and Exercise Metabolism, 21(1): 55-64.
Gleeseon, M., Bishop, N. C., Oliveira, M, McCauley, T. (2012). Effects of a Lactobacillus salivarius probiotic intervention on infection, cold symptom duration and severity, and mucosal immunity in endurance athletes, International Journal of Sport Nutrition and Exercise Metabolism, 22(4): 235-242.
Haywood, B. A., Black, K. E., Baker, D., McGarvey, J., Healey, P. & Brown, R. C. (2014). Probiotic supplementation reduces the duration and incidence of infections but not severity in elite rugby union players, Journal of Science and Medicine in Sport, 17: 356-360.
Kekkonen, R. A., Vasankari, T. J., Vuorimaa T., Haahtela, T. (2007). The effect of probiotics on respiratory infections and gastrointestinal symptoms during training in marathon runners, International Journal of Sports Nutrition and Exercise Metabolism, 17(4): 352-363.
Nieman, D. C. (1994). Exercise, upper respiratory tract infection and the immune system, Medicine and Science in Sports and Exercise, 26(2): 128-139.
Pyne, D. B., West, N. P. & Cripps, A. W. (2014). Probiotics supplementation for athletes – clinical and physiological effects. European Journal of Sport Science,
Reid, V. L., Gleeson, M., Williams, N., Clancy, R. L. (2004). Clinical investiation of athletes with persistent fatigue and/or recurrent infections, British Journal of Sports Medicine, 38: 42-45.
West, N. P., Pyne, D. B., Cripps, A. W., Hopkins, W. G., Eskesen, D. C., Jairath, A., Christophersen, C. T., Conlon, M. A. & Fricker, P. A. (2011). Lactobacillus fermentum(PCC) supplementation and gastrointestinal respiratory-tract illness symptoms: a randomised control trial in athletes, Nutrition Journal, 10(30): 1-11.

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