Background: Antigen exposure is one of the major exogenous factors modulating human immunocompetence acquisition. Decline in family size and improvements in public health and hygiene in developed countries, may deprive the immune system of appropriate antigen input by diminishing infectious stimuli. Probiotics are a large group of microorganisms defined by their beneficial effects on human health and with stimulating effects on different functions of the immune system.
Aim of the study: We conducted a double-blind, placebo-controlled trial to determine if probiotics maintain their immune-stimulating effects in a population of 162 children with a high index of natural exposure to microorganisms. Children were to ingest for at least 4 months one of two products, low-fat milk fermented by Streptococcus thermophilus (control product) or low-fat milk fermented by S. thermophilus and Lactobacillus casei, with Lactobacillus acidophilus, oligofructose and inulin added after the fermentation process (test product). According to their age, children were vaccinated with DTP-Hib vaccine or a 23-valent anti-pneumococcal vaccine.
Results: Final analysis of results was done in 70 children in each group, showing that the rate of immunoglobulin and isoagglutinin acquisition was similar in both groups. There was no difference between groups in antibody levels neither before nor after vaccination. Days of fever and number of episodes of infection were not statistically different in either group.
Conclusions: Supplementation of standard fermented milk with additional probiotics was not of benefit. The high natural rate of early microbial exposure in infants and children from a population of low socio-economic status living in a "less hygienic environment" may account for the absence of an additional immune-stimulating effect by supplementary probiotics.