Probiotics cut the odds of catching a cold, but not how long one drags on

Acute upper respiratory tract infections, the everyday colds and sore throats, are among the most common reasons people feel unwell and end up prescribed antibiotics they may not need. Probiotics, live bacteria taken as supplements or in foods, are thought to influence immune function, and some individual studies had hinted they could ward off respiratory infections. Before this review, however, no pooled assessment of their benefits and potential harms for preventing these infections had been published. Whether a cheap and generally safe supplement can reduce infections and antibiotic use is a question with genuine public health weight.

This Cochrane review searched major medical databases, including several Chinese-language sources, for randomised trials comparing probiotics against placebo for preventing acute upper respiratory tract infections. Fourteen trials met the criteria, and usable data from 10 of them, covering 3451 participants, were pooled in a meta-analysis. Two reviewers independently assessed eligibility and trial quality and extracted the data. The outcomes examined included how many people experienced infection episodes, how often episodes occurred, how long they lasted, antibiotic prescription rates and adverse events.

People taking probiotics were less likely than those on placebo to experience at least one acute upper respiratory infection, and also less likely to suffer at least three episodes. The overall rate of episodes was lower, and antibiotic prescriptions for these infections fell as well. Once an infection struck, though, probiotics made no measurable difference to how long it lasted. Adverse events were similar between groups and minor, with gastrointestinal symptoms the most common, although some of the pooled comparisons showed the trials disagreeing with each other.

According to the authors, this was the first pooled assessment of probiotics for preventing these infections, moving the idea from scattered single trials to a consistent overall signal. It fits the broader notion that gut bacteria interact with immune function, without explaining the mechanism. Important gaps remain: the review found no data at all for older people, and the variation between trials means the true size of the benefit is uncertain. Which strains and doses matter most is also unresolved.

This is a reason to think probiotics may modestly lower your chances of catching a cold, not a guarantee of protection. It is not a reason to expect a probiotic to shorten a cold you already have, since episode duration did not budge at all. The safety picture was reassuring, with side effects no worse than placebo and mostly limited to minor gut complaints. If you are an older adult, note that this evidence simply does not cover your age group yet.