We carry them around with us everywhere we go, outnumbering our own cells ten to one. But over the past decade, research has increasingly been hinting that the freeloading, hitchhiking bacteria that cover us might actually be contributing far more than we thought. So much so that they could actually be affecting our behavior.
Researchers from The Ohio State University have found that the abundance and diversity of bacteria found in the gut appear to influence the behavior of young children, especially boys. They found that children with the most genetically diverse composition of bacteria are more likely to show behavior related with positive mood, curiosity, sociability, and impulsivity. But the researchers point out that they’re still unsure if it’s the bacteria influencing the brain, or the other way around.
“There is definitely communication between bacteria in the gut and the brain, but we don't know which one starts the conversation,” said Dr. Michael Bailey, who co-authored the study published in Science Direct. “Maybe kids who are more outgoing have fewer stress hormones impacting their gut than shy kids. Or maybe the bacteria are helping mitigate the production of stress hormones when the child encounters something new. It could be a combination of both.”
It used to be thought that the vagal nerves that connect the brain with the gut were a one-way system, and that the brain told the gut what to do and that was that. But evidence has been mounting that, in fact, it’s far more of a two-way street then we thought. For example, it’s now known that around 90% of the body’s serotonin—the so-called “happy hormone”—is actually produced in the digestive tract, and that people who suffer from a range of psychological disorders also experience gastrointestinal problems.
“There is substantial evidence that intestinal bacteria interact with stress hormones—the same hormones that have been implicated in chronic illnesses like obesity and asthma,” said Lisa Christian, another of the study’s authors.
The researchers analyzed the gut bacteria from children aged between 18 and 27 months, and then looked to see how these compared with the children’s temperaments. They found that the correlation between bacteria and behavior continued even when they factored in things such as method of birth, breastfeeding, and diet, which are all known to affect a child’s microbiome. In boys only, they found a link between extrovert behavior and the abundance of microbes from the Rikenellaceae and Ruminococcacae families and Dialister and Parabacteroides genera.
But if parents are looking for an easy way to solve their child’s terrible twos, altering their gut microbiome might not, unfortunately, be the answer. It’s still unknown what a healthy combination of gut bacteria might look like, or how they might influence other aspects of a child’s behavior or health. “The bacterial community in my gut is going to look different than yours—but we are both healthy,” explained Bailey.