What does intestinal microbiota (i.e. the “good” bacteria that live in our intestine) have to do with depression? A lot, according to a report published in the scientific journal Nature Microbiology by a team from the Catholic University of Lovanio, in Belgium.
The researchers analyzed the microbiota of 2000 people living in Holland and Belgium and concentrated mainly on the presence of the genetic traces of 532 different strains of bacteria and on the ability of these organisms to synthesize the important substances required for the production of neurotransmitters (the molecules used by nerve cells to communicate with one another). The researchers then compared the results of this map with the psychological conditions of the people that “hosted” the bacteria, and they discovered interesting connections between the two.
First of all, 90% of the analysed microorganisms appeared to be involved, in different ways, in the productive cycle of dopamine and serotonin, fundamental neurotransmitters for regulating mood. Furthermore, evident alterations were discovered in the microbiota of depressed patients: in particular, low levels of the Dialister and Coprococcus bacteria, already known to produce a precursor of dopamine. In reality – specify the Belgian researchers – it is not possible to associate this reduced presence of bacteria for certain also with a low production of neurotransmitters (and therefore with a greater tendency towards depression). The opposite could also occur, write the researchers, where it is the depression that causes the reduced presence of Coprococcus and Dialister, in ways yet to be defined (and therefore the reduced levels of these bacteria would be an effect, and not the cause, of depressive syndromes).
The study conducted by the researchers in Lovanio, in any case, confirms that there are significant connections between mood change and the composition of microbiota, even if the relationship between the two does not seem easy to decipher. On the other hand – the researchers also highlight – the vagus nerve, which extends from the lower part of the brain to the intestine (and is the longest in the body) is capable of transporting information and molecules in both directions: therefore it really could be a kind of highway for regulating mood, even if the “rules on the direction of travel” are not yet clear.
Dialister bacteria is a further confirmation of the complexity of the balance between microbiota and other systems in the body: when it is present in very low amounts, as we said, it is associated with depression but if, on the other hand, it grows beyond the norm, it is related to an increased risk of developing arthritis. It will be difficult, or impossible, to use microbiota in new pharmacological therapies to treat psychiatric illnesses or auto-immune diseases until more is known about these relationships. “However, this perspective, which is so outside-the-box, is very interesting”, commented Emma Allen-Vercoe, professor of microbiology at the University of Guelph (Canada), “Thanks to these studies, we are embarking on a completely new path”.