Exposure of children early in life to bacteria in the environment is essential for the development of the immune system and therefore plays a vital role in the prevention of several autoimmune diseases such as type i diabetes, asthma and the allergies.
Autoimmune diseases are caused by imbalances in the immune system: instead of limiting itself to defending the body from external aggressions, as is normally the case, immunity instead attacks the human body itself. This target error obviously has serious consequences and can lead to the development of a large number of pathologies, including type I diabetes, inflammatory bowel disease, lupus, asthma or even allergies.
The incidence of autoimmune diseases has been increasing sharply in recent years and several scientists have hypothesized that this increase could be linked to the drastic decrease in microbes present in our living environment. According to this theory, called the “hygiene hypothesis”, the constant improvement of sanitary conditions decreases our exposure to different microbes in the environment and causes immunity not to come into contact with enough microorganisms. to properly learn its role and adequately distinguish what is dangerous (pathogens from outside) from what is not (the human body as such).
In this sense, it is interesting to note that children who grow up in an environment rich in microbes, such as a farm, are much less affected by asthma and allergies. The factors responsible for this protection remain poorly understood, but it is likely that the intestinal microbiota, that is to say the community of bacteria present in the intestine, plays an important role, since several studies suggest that these bacteria are essential for the proper functioning of immunity.
The standard of living increases and immunity decreases
To better understand this phenomenon, scientists had the idea of studying the composition of the microbiota of three populations that live very close to each other (Finland, Russian Karelia and Estonia), but which nevertheless have very different from autoimmune diseases. Finland and the Russian Republic of Karelia are indeed geographically glued to each other, but the incidence of allergies and type I diabetes is up to six times higher in Finland. Estonia, on the other hand, is located in the same region and until recently had a similar incidence of autoimmune diseases as Karelia, but industrialization and improved living standards have led to a rise in incidence of these diseases, now similar to that of Finland.
Overuse of antibiotics weakens children’s immunity
To carry out the study, the scientists collected stool samples every month for three years from more than 200 children born in Espoo (Finland), Petrozavodsk (Karelia) and Tartu (Estonia). The bacterial composition of these stools was analyzed by genetic sequencing and the general state of health of the children was determined in parallel using a very detailed questionnaire.
The scientists first observed that the bacterial composition of the microbiota was very different depending on the place of birth: the intestinal flora of Finnish and Estonian children was dominated by Bacteroides species, while that of children from Karelia in Russia was mainly composed of Bifidobacteria.
This difference certainly has important consequences for the development of the immune system, since the researchers observed that the immune activity of the microbiota enriched in Bacteroides was abnormally low compared to that enriched in Bifidobacteria.
In other words, it seems that the sanitary conditions associated with the modern way of life favor the increased presence of certain bacteria in Finnish and Estonian children (Bacteroides) and that these bacteria prevent the immune system from developing normally. Conversely, the microbiota of Russian children is more representative of that which we have developed during the evolution of the human species and therefore allows optimal development of immunity.
These results remind us that despite its generally positive repercussions in our lives, the improvement of sanitary conditions also has a negative impact on the diversity of the intestinal flora.
It is not a question of going back, far from it, but of taking these observations into account in order to reduce this negative effect as much as possible. One of the most important aspects is to limit, when possible, the use of antibiotics, which have a devastating effect on the intestinal flora, especially since they are often totally useless, because the infection that they are supposed to cure is caused by viruses (which are insensitive to antibiotics).
The abundant consumption of foods of plant origin can also have a major impact on the composition of the intestinal flora, since the presence of fibers and dietary polyphenols allows the establishment of a diversified microbiota, composed mainly of beneficial bacteria.
Von Mutius E and D Vercelli. Farm living: effects on childhood asthma and allergy. Nature Rev Immunol; 10:861-8.
Vatanen T et al. Variation in microbiome LPS immunogenicity contributes to autoimmunity in humans. Cell 2016; 165: 842-853.