The gut microbiota lives in close contact with the intestinal barrier and molecules such immunoglobulin A produced by plasma cells in the lamina propria. The fact that the large proportion of the immune system in the human body is located within the intestine-especially the small intestine but also the large intestine-has led scientists to explore the role of probiotics in immune function.
For instance, one mechanism by which probiotic bacteria might modulate the human immune system is by increasing antibody response, decreasing inflammation and stimulation of phagocytosis. However, to what extent probiotics, especially in form of fermented dairy drinks, can affect immune function in the healthy population has been poorly studied.
A new systematic review and meta-analysis of randomized controlled trials concludes that a fermented dairy milk with probiotic bacteria may reduce respiratory and gastrointestinal tract infections in healthy children and adults, but with no effects on their duration or severity.
The authors included in the analysis nine randomized controlled trials exploring the effects of a fermented dairy drink which contained the probiotic bacterium Lacticaseibacillus paracasei subsp. paracasei CNCM I-1518 with standard yogurt cultures on the incidence, duration, and severity of upper and lower respiratory tract infections and gastrointestinal tract infections in generally healthy children and adults aged 2 years and older (2 studies in children, 3 studies in adults and 4 studies in older adults).
The efficacy and safety of this probiotic strain was grounded in previous studies that supported the strain’s role in modulating some immune markers. In fact, it has been suggested that this probiotic bacterium may enhance host immunity by modulating the gut microbiota, epithelial barrier, and local mucosal immune response.
The consumption of the probiotic fermented dairy drink reduced the incidence of respiratory and gastrointestinal tract infections compared to a placebo or control intervention, as measured by the number of subjects experiencing one or more infections. However, the probiotic fermented dairy drink had no effect on the duration or severity of infectious diseases.
Some limitations of the human intervention studies featured in the meta-analysis included failing to consider confounders (e.g., self-reporting of infections without diagnosis by a physician), the low study quality reported in some studies, high levels of heterogeneity, and occasional insufficient data for assessing publication bias.
In conclusion, the findings suggest fermented dairy drinks with probiotic bacteria may help reduce the appearance of new cases of respiratory and gastrointestinal tract infections that are common in generally healthy children and adults. Probiotics per se will not prevent or cure an infection, but in the light of current findings, this seems a plausible approach for supporting the immune system in the context of a balanced diet.
Spencer J, Sollid LM. The human intestinal B-cell response. Mucosal Immunol. 2016; 9(5):1113-1124. doi: 10.1038/mi.2016.59.
Poon T, Juana J, Noori D, Jeansen S, Pierucci-Lagha A, Musa-Veloso K. Effects of a fermented dairy drink containing Lacticaseibacillus paracasei subsp. paracasei CNCM I-1518 (Lactobacillus casei CNCM I-1518) and the standard yogurt cultures on the incidence, duration, and severity of common infectious diseases: A systematic review and meta-analysis of randomized controlled trials. Nutrients. 2020; 12(11):3443. doi: 10.3390/nu12113443.