Eating fermented probiotic dairy products may prevent pneumonia and common colds in children, adults and the elderly, a new study suggests.
The study, “Effect of probiotic fermented dairy products on incidence of respiratory tract infections: a systematic review and meta-analysis of randomised clinical trials, was published in Nutrition Journal.
Respiratory tract infections (RTIs)– infections that affect parts of the body involved in breathing, such as the sinuses, throat, airways or lung – are a leading cause of antibiotic use, hospital admissions and death.
Upper respiratory tract infections (URTIs) affect the sinuses and throat. They are often mild to moderate and resolve spontaneously. However, lower tract respiratory infections (LTRIs), which affect the airways and lungs, are more severe and can be fatal in children, the elderly, and people with weak immunity.
Probiotics are living bacteria and fungi with possible health benefits. They include species such as lactobacillus and Bifidobacterium and are usually added to food or taken as supplements to reduce antibiotic use, prevent infections and strengthen immunity.
Probiotics are present in many fermented foods such as soy and dairy products.
Previous studies assessing the effects of probiotic dairy products against RTIs have produced conflicting results for various reasons, including differences in experimental designs, sample sizes and bacterial strains used to prepare fermented dairy products.
A team of researchers sought to resolve the inconsistency problem and ascertain the effects of probiotic dairy products on RTIs by conducting a comprehensive review and reanalysing published studies in the subject area.
After excluding studies that did not meet the inclusion criteria, a total of 22 clinical trials with a sample size of 10,190 were included in the analysis.
When the studies were combined, the researchers found that compared to placebo, consumption of probiotic dairy products reduced RTI risk in all age groups by 19%. RTI risk was reduced by 18, 19, and 22% in children, adults, and the elderly, respectively.
In general, probiotic dairy products were more protective against URTIs than LRTIs. They were also specifically protective against pneumonia and common colds but had no significant effect on other RTIs.
Moreover, the probiotics seemed to be most effective if they were made from lactobacillus and milk. Combining Bifidobacterium with dairy drinks or yoghurt did not show a protective effect.
Past studies show that unlike products made with other bacteria, lactobacillus-containing products are resistant to stomach acids and bile and successfully reach the large intestine without destruction. Once there, they rebalance gut bacteria and promote the production of immune cells that can move to other parts of the body and protect them from infections.
A lack of protective effect was evident with Bifidobacterium-containing drinks, possibly because only a few studies investigated their impact on RTIs. Consequently, the researchers suggest these results be interpreted cautiously.
Study limitations the researchers wrote included searching only English-written publications and the large differences between studies, particularly in their designs and the type of bacteria and dairy products used.
“Considering all facts…our analysis indicated protection effect of fermented probiotic dairy products against RTIs in all age subgroups,” they wrote.
“Reduction of RTIs by fermented probiotic dairy products is highly important if it is accompanied by a reduction in medication use, working and school days loss, and social burden.”