With each new study on bacterial flora, the idea that in each body there are two entities, on the one hand, the human being, on the other, its microbiome. And it's good that they get along. Recent work has shown the connection of certain intestinal bacterial profiles with mental health, even going down to the level of identifying types of bacteria associated with depression. But, if some microbes can be behind mental illnesses, can there be others that promote better cognition? This is what a group of scientists point out who have studied the relationship between the cognitive abilities of hundreds of children with the little bugs they have in their bellies.
Everything indicates that children develop in their mother's womb in a sterile environment, free of bacteria. “It is when they pass through the vaginal tract that they receive a bath from them,” said the Spanish professor at the Icahn School of Medicine at the Mount Sinai Hospital in New York, José Clemente, a few years ago after performing a first maternal microbiome implant. children born by cesarean section. The bacterial bath is vital. Maternal intestinal and vaginal microbes thus colonize your body to facilitate key functions, such as training the immune system or supporting the digestive system. During the first months, breast milk or formula shapes this first intestinal microbiome. And it is not until the transition to solid food, when the profile of its flora begins to resemble that of adults.
In parallel, the brains of children go through the greatest transformations they will have in their entire lives: Myelination becomes generalized, the development of protective sheaths of the axons, the endings of the neurons. The critical phase of so-called synaptic pruning begins, a process by which most of the unnecessary connections formed almost haphazardly in the first years of life are eliminated. Neurogenesis, initiated in the fetus, experiences its most productive years. At five years old, a child's brain reaches 85% of the size it will be as an adult. And it is at this time when the general pattern of brain connections is fixed, leaving a margin for plasticity that narrows even more at the end of adolescence.
A large group of researchers, neurologists and pediatricians in the United States have sought possible relationships between this rapid brain and mental development in 381 children, the youngest just 40 days old and the oldest 10 years old, with their intestinal flora. The research, recently published in the scientific journal Science Advancesstarted from the idea that if certain bacterial profiles can be related to or even behind certain mental pathologies, why wouldn't other groups of bacteria be influencing the anatomy and cognition of the brains of children.
To identify the intestinal flora, they analyzed stool samples from the children, including a genetic analysis to classify the different species, genera and families of bacteria and their functions in metabolism. In parallel, they carried out a series of tests adapted to each person's age to determine the degree of their cognitive abilities. The data collection work was completed with a series of scans of the brains to determine their anatomy in detail.
The main difference was expected and has to do with age. Children six months or younger have a smaller number and variety of bacteria in their intestines. Things change especially after 18 months, with an increase in both the diversity of species and the number of their numbers. But research has also detected parallel variation, suggesting a connection, between the microbiome and results on different cognitive tests. Specifically, certain intestinal microbial species, such as Alistipes obesi, Faecalibacterium prausnitzii and Blautia wexlerae , have a greater presence in the intestines of children who achieved the best test scores. Conversely, they found that species like Ruminococcus gnavus either Sutterella wadsworthensis They are more common in children with lower cognitive outcomes.
“Bacteria can produce molecules that directly influence the nervous system.”
Kevin Bonham, microbiologist and immunologist at Wellesley College, United States
The work goes a little further and studies the possible connection of specific species with certain abilities. In the same way that some bacteria have a metabolic function, such as processing a certain fatty acid, they also seem specialized in some dimensions of cognition and not others. What they have observed, for example, is that two species of the genus Streptococcus (S. peroris and S. mitis) and the Bacteroides fragilis They abound in the little ones with better linguistic expression. For their part, bacteria Roseburia faecis, Streptococcus salivariusand Fusicatenibacter saccharivorans could be involved in gross motor skills, and Clostridium innocuum and Bacteroides vulgatus They are very popular in the intestines of children who excelled in visual perception.
The microbiologist and immunologist at Wellesley College (United States) and first author of the research, Kevin Bonham, immediately cautions against drawing hasty conclusions: “There are some mechanisms [de la conexión entre microbios y función cognitiva] “That have been shown in other contexts, but I want to emphasize that in this study we were only looking at associations and cannot make any claims about causality.” But it does recall some mechanisms by which microbes could be causally connected. “One is that bacteria can produce molecules that directly influence the nervous system,” he says. Indeed, the intestinal flora generates dopamine or serotonin during its metabolic activity, two neurotransmitters. “In others, they can activate the immune system and many of the immune signals can affect the brain,” he adds. For example, certain bacterial species produce neuroactive components, such as short-chain fatty acids (butyrate or propionate) that reduce inflammation.
Bonham's research and the head of her laboratory, Vanja Klepac-Ceraj, senior author of the research, used in her work a catalog of these neuroactive components prepared, among others, by Mireia Vallès Colomer, who leads the Microbiome Research Group at Pompeu Fabra University (UPF). “For many years, she talked about people with depression, with Parkinson's, with Alzheimer's, who had a greater abundance of some bacteria and less of others. She liked to identify them, give them a name. But what we see is that the microbiome is a supercomplex ecosystem, the most important thing is not whether there is one bacteria or another, but the composition at the function level, which bacteria reduce inflammation, which ones produce serotonin…”, explains the microbiologist. That functional catalog was carried out within the framework of research on the microbiome and depression. The big news now is its use in children and healthy children. But neither in children nor in depressives has the cause-effect relationship been established yet.
“It has been proven, in mice, that if you give them bacteria that are not abundant in people with depression, their symptoms improve”
Mireia Vallès Colomer, microbiologist at Pompeu Fabra University
“In humans, it still cannot be confirmed,” Vallès highlights. “When we publish our research In 2019, articles appeared with headlines like Depression bacteria discovered. But, for now, the only thing we know is that people who have depression have effects on the microbiome, but it is not known if it is the depression that causes this alteration, the other way around, or none of them. But, then, he highlights that “it has been proven in mice, with which this type of studies can be done, that if you give them bacteria that are not abundant in people with depression, they improve in several symptoms.”
The dean of the Faculty of Medicine of the University of Girona, Dr. José Manuel Fernández-Real, has been researching the microbiome-gut-brain axis for years. His work has been pioneering, for example, in illustrating the mediation of the metabolic activity of the intestinal flora in the connection between obesity and deficits in both short-term and working memory. Regarding the methodology of the new study, he has serious doubts: “They did not use conventional statistical techniques to analyze the composition of the microbiota, which is essential to avoid erroneous associations in the presence of a large volume of data,” he highlights. For him, “a more exhaustive review and the use of robust statistical techniques would be desirable to strengthen the validity of the results and adequately contextualize the contribution of this study to the field.”
This is not to say that I reject the connection between flora and cognition. In the adult population, “the link between the intestinal microbiota profile and cognitive functions has been extensively investigated,” recalls Fernández-Real. For example, it has been suggested that “a balanced microbiota (in the context of a Mediterranean diet) can contribute positively to the preservation of brain function,” she adds. Although the how is what is being more complicated to unravel, everything indicates that the bidirectional communication between the intestine and the brain, the aforementioned gut-brain axis, could play a crucial role. The dean details it: “Metabolites produced/metabolized by intestinal bacteria, such as short-chain fatty acids, may have neuroprotective effects and be related to cognitive function.”
There are already companies to which you can send a stool sample so that they can create a profile of your personal microbiome, accompanied by the absences and stocks of the bacteria catalogue. But Bonham doesn't believe there are probiotics to make kids smarter or more savvy: “It's possible that this will happen one day, but the effect sizes here are very small and, in any case, we're a long way from that,” Lo says. More important to him is that “chances are that someday we will be able to identify risk factors that could help us identify children who might need a little more help, but I suspect that help will come from things that we already know.” “We know how to deal with it and not so much about changing the microbiome.”
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