Probiotic Supplementation and Respiratory Infection and Immune Function in Athletes: Systematic Review and Meta-Analysis of Randomized Controlled Trials

Objective To evaluate the effectiveness of probiotic supplementation on upper respiratory tract infection (URTI) and inflammatory markers in elite athletes. Data Sources We searched the PubMed, EBSCOhost, Scopus, and Web of Science databases using the following terms: probiotic OR probiotics AND exercise OR sport OR athletes AND URTI OR respiratory infection OR URTIs OR inflammation OR inflammatory OR cytokines. Study Selection We screened the titles and abstracts of 2498 articles using our inclusion criteria. A total of 14 articles were selected for further analysis. Data Extraction For each study, 2 independent reviewers extracted the study design, participant characteristics, inclusion and exclusion criteria, intervention characteristics, outcome measures, and main results. Data Synthesis We did not observe an effect of probiotic supplementation on the number of days of illness or the mean number or duration of URTI episodes but did note an effect of probiotic supplementation on the total symptom severity score (−0.65; 95% CI = −1.05, −0.25; P = .02). Lower levels of interleukin 6 (−2.52 pg/mL; 95% CI = −4.39, −0.66 pg/mL; P = .002) and tumor necrosis factor α (−2.31 pg/mL; 95% CI = −4.12, −0.51 pg/mL; P = .01) were also reported after supplementation. Conclusions This meta-analysis provides evidence that probiotic supplementation, especially among professional athletes, is an effective way to decrease the total URTI symptom severity score. In addition, probiotic supplementation may decrease interleukin 6 and tumor necrosis factor α levels. More studies involving larger groups are needed to better assess this effect. The optimal timing, duration, composition, and dose of such supplementation need to be determined.