While dietary supplementation, nutrition and physical activity have been studied extensively for their respective roles in modulating the immune system response, specific strains of probiotics have also shown promise in the prevention of upper respiratory tract infection (URTI).
A meta-analysis of 20 randomised controlled trials (RCTs) demonstrated that probiotics are capable of reducing the duration of illness of upper respiratory tract infection, and are associated with a statistically significant reduction sick days spent away from school, work and day care amongst those taking probiotics compared to placebo. The results of this review of a number of good quality RCTs suggests that probiotics can reduce duration of illness in otherwise healthy children and adults. It is important to note that different strains and doses of probiotics can have variable effects and some strains have more evidence than others.
A randomized, placebo-controlled study looked at the effect the probiotic Lactobacillus plantarum had on reducing the duration of URTIs. Results showed that the administration of L. plantarum DR7 reduced the proportion of patient days of URTI when compared to placebo for all parameters studied including reduced average duration of URTI symptoms, and total number of days with fever, as well a reduction in the use of URTI-related medication, suggesting there may be an important role of probiotics in decreasing bacterial resistance to antibiotics by reducing overall antibiotic use. It is important to note that this study only reported on one specific strain of probiotic and the efficacy of the probiotic will depend on the strain and its core mechanism of action. It should also be noted that the patient's specific history of infection and the start point of probiotic administration will have an influence on the outcome of probiotic therapy.
Respiratory infections have also been reported to create dysbiosis in the gastrointestinal tract, for which probiotics have been extensively shown to play an important role in rebuilding the microflora.
1. King, S., Glanville, J., Sanders, M., Fitzgerald, A., & Varley, D. (2014). Effectiveness of probiotics on the duration of illness in healthy children and adults who develop common acute respiratory infectious conditions: a systematic review and meta-analysis. The British Journal of Nutrition, 112(1), 41-54.
2. Microorganisms - Effects of a Lactobacilli Probiotic on Reducing Duration of
URTI and Fever, and Use of URTI-Associated Medicine: A Re-Analysis of a Randomized, Placebo-Controlled Study, source: https://www.mdpi.com/