What are probiotics and what are they used for?

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Probiotics are microorganisms, yeasts or bacteria, promoting the balance of intestinal flora. According to the official definition of the “World Health Organization” (WHO), probiotics are living organisms that, administered in adequate quantities, bring a benefit to the health of the host. 

To be defined as a probiotic, a microorganism must have some peculiar characteristics, including the following:

1. It colonizes the human intestine and multiplies within it;
2. It must not be harmful to human health;
3. It must bring some beneficial effect.

The first studies that attributed the ability to positively influence human health and aging to certain microorganisms are attributed to the Russian scientist Metchnikoff, Nobel Prize winner for Medicine in 1908. From Metchnikoff onwards, the study of probiotics has been in continuous ferment, reaching its peak in recent years thanks to the development of cutting-edge technologies that have allowed a better characterization.

The most-studied organisms are those that naturally reside in the human intestine and that make up the so-called “intestinal microbiota”. They live in symbiosis with us, help us during digestion, provide us with nutrients and protect us from pathogens; in return, we provide them with a constant supply of food and protection. The composition of the intestinal microbiota has evolved with us and, although with many similarities, its composition is specific for each individual.

The colonization of the intestine begins during fetal life, is greatly enriched during childbirth and breastfeeding, to be then quantified during the first years of life. Although their number remains approximately equal, their composition changes during our life. The type of diet, the lifestyle, the various moods and the use of drugs are the major factors influencing the composition of our intestinal microbiota. A recent study, conducted by the University of Copenhagen, analyzed the effects on the intestinal microbiota of a four-day treatment with a mix of three antibiotics on healthy men. After the cure, the intestinal microbiota had almost completely disappeared, reconstituting itself only after six months. Moreover, after this period, nine beneficial bacterial species initially present had not yet reappeared and new potentially undesirable bacterial species had colonized the gut of thesample. The study highlighted the effect that antibiotic therapy has on intestinal microbiota and how the abuse of these drugs is potentially dangerous when not necessary.

Scientific research is significantly focusing its attention on understanding the role of intestinal microbiota in different pathologies. Surprisingly, researchers have observed that these microorganisms not only play an important role in gastrointestinal diseases (ulcers, Crohn’s disease, chronic inflammation and intestinal infections). Among these, we find pathologies affecting the nervous system (depression, Alzheimer’s and Parkinson’s) as well as chronic autoimmune and inflammatory diseases (systemic lupus erythematosus, rheumatoid arthritis, spondyloarthritis, and multiple sclerosis). The mechanisms by which the intestinal flora manages to influence areas of the body far from their initial localization are not yet completely clear; it is hypothesized that such effect is due to both their continuous dialogue with the intestinal immune system (which represents about 70% of the entire body) and the release of substances that, once in the bloodstream, reach all regions of the body, even the most distant ones.

Given their effects in different pathologies, these supplements are widely used. It is not yet clear what the “effective dose” of each microorganism should be; that is, the quantity of living and vital bacterial cells to be administered to an individual, so that they can restore normal bacterial flora. This value is closely linked to the characteristics of the species used and in particular to their ability to adhere to intestinal epithelia. The law establishes that, in order to be defined as “probiotic”, a food or a supplement must contain at least one billion live and viable microorganisms and that the use of a lower number must be justified by scientific studies.

Given the number of microorganisms in a supplement, how long should a probiotic be taken to restore normality? Even this point is not yet completely clear as new discoveries follow one another every day. The treatment may last a few days in the case of a diarrhea induced by an antibiotic therapy or a few months for more complicated cases. A long treatment could be necessary so that the microorganism has the time and the strength to colonize its own corner of intestine, survive inside it and be able to multiply. The duration of the treatment is often underestimated. This represents one of the major causes of failure of this approach. Scientific research is making giant steps in the characterization of intestinal microbiota, trying to outline how their alteration can influence the appearance and progression of different pathologies. The whole scientific community is confident that the potential of probiotics is enormous.