The effect and safety of probiotics in the prevention of acute upper respiratory tract infections (URTIs) in 3720 participants of all ages were assessed in the Cochrane systematic review of 12 randomised controlled trials.
The results of the meta-analysis suggested that probiotics may be effective in reducing the number of participants with episodes of acute URTIs by about 47%, the duration of an episode by about 1.89 days, antibiotic use and school absence due to colds. Adverse events of probiotics were minor. However, the authors concluded that better conducted randomised controlled trials are needed to confirm these findings.
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Reference: Hao Q et al. Probiotics for preventing acute upper respiratory tract infections. Cochrane Database Syst Rev 2015, Issue 2. Art.No.: CD006895