Probiotics for preventing acute respiratory tract infections

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Plain language summary

Can probiotics (live micro‐organisms) prevent upper respiratory tract infections such as the common cold?

Key messages

Probiotics may be beneficial in preventing at least one occurrence of acute upper respiratory tract infection (URTI), and are likely beneficial in preventing at least three occurrences of URTIs. More studies conducted in the elderly are needed. Larger, well‐designed studies are needed to give better estimates of the benefits and potential harms of probiotics use.

What are acute upper respiratory tract infections?

Acute URTIs include colds, influenza, and infections of the throat, nose, or sinuses. Symptoms include fever, cough, pain and headaches. Most acute URTIs are caused by viruses, and usually get better within three to seven days. 

What are probiotics?

A common description of probiotics is live micro‐organisms that give a beneficial effect to the body when consumed in adequate amounts. Lactic acid bacteria and bifidobacteria are the most common types and are commonly consumed in fermented foods, such as yoghurt and soy yoghurt, or as dietary supplements.

What did we want to find out?

We wanted to find out if probiotics prevent acute URTIs in people of all ages with a healthy immune system.

What did we do?

We searched for studies that investigated probiotics for URTIs. We compared and summarised the results of the studies, and rated our confidence in the evidence, based on factors such as study methods and sizes.

What did we find?

We found 24 studies. We analysed data from 6950 people, including children (aged from 1 month to 11 years old), adults (mean age 37.3 years), and older people (mean age 84.6 years) from Italy, Japan, the United States, Croatia, England, Finland, Sweden, Chile, China, Denmark, Germany, Thailand, and Turkey. It was not clear in which countries two trials were conducted. Most of the studies were conducted in the community, care facilities, schools, and hospitals for three months during the winter/spring. Probiotics were more likely to be given with milk‐based food in children, in powder form in adults, and with milk‐based food or capsules in the elderly. One or two strains (e.g. Lactobacillus plantarum HEAL9, Lactobacillus paracasei (8700:2 or N1115)) and 109 or 1011 colony‐forming units (CFU)/day of probiotics were used in most of the studies. 

Main results

Probiotics may reduce the number of people diagnosed with at least one URTI by about 24%; likely reduce the number of people diagnosed with at least three URTIs by about 41%; may reduce the incidence rate (number of new cases during a specified period of time) of acute URTIs by about 18%; may reduce the mean duration of an episode of acute URTIs by about 1.22 days; likely reduce the number of people who used antibiotics for URTIs by about 42%; and may not increase the number of people who experienced side effects (any harm). Evidence showing a decrease in the number of people absent from childcare centre, school, or work due to acute URTIs with probiotics was very uncertain. 

What are the limitations of the evidence?

We are moderately confident that probiotics decrease the number of people diagnosed with at least three URTIs and the number of people who used antibiotics for URTIs, and have low confidence in the evidence that probiotics decrease the number of people diagnosed with at least one URTI, the incidence rate of acute URTIs, the mean duration of an episode of acute URTIs, and increase the number of people who experienced side effects (any harm). Evidence showing a decrease in the number of people absent from childcare centre, school, or work due to acute URTIs with probiotics was very uncertain. The main reasons for the limitations of the evidence were that people in the studies may have known which treatment they were getting, and not all of the studies provided data about everything that we were interested in.

How up‐to‐date is the evidence?

The evidence is current to 10 May 2022.