The abundance and diversity of certain types of gut bacteria appear to impact toddler behavior, particularly among boys, according to new research from Ohio State University. Gut bacteria may interact with stress hormones to produce behavioral and physical 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, Ph.D, a researcher with Ohio State’s Institute for Behavioral Medicine Research.

“A toddler’s temperament gives us a good idea of how they react to stress. This information combined with an analysis of their gut microbiome could ultimately help us identify opportunities to prevent chronic health issues earlier.”

For the study, researchers analyzed microbes from the gastrointestinal tracts of children between the age of 18 and 27 months. They found that the connection between gut bacteria and behavior remained consistent after the scientists factored in history of breastfeeding, diet, and the method of childbirth — all of which are known to influence the type of microbes in a child’s gut.

The researchers are looking for clues into how — and where — chronic illnesses such as obesity, asthma, allergies, and bowel disease get their start.

Christian and study co-author microbiologist Michael Bailey, Ph.D., studied stool samples from 77 girls and boys, and found that children with the most genetically diverse types of gut bacteria more frequently exhibited behaviors related with positive mood, curiosity, sociability, and impulsivity.

In boys only, researchers reported that extroverted personality traits were associated with the abundances of microbes from the Rikenellaceae and Ruminococcaceaefamilies and Dialister and Parabacteroides genera.

“There is definitely communication between bacteria in the gut and the brain, but we don’t know which one starts the conversation,” said Dr. Bailey, who is currently a researcher with Nationwide Children’s Hospital and a member of Ohio State’s Institute for Behavioral Medicine Research.

“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.”

Overall, the connection between temperament and the gut microbiome in girls was less consistent than in boys. However, in girls, behaviors like self-restraint, cuddliness, and focused attention were connected to a lower diversity of gut bacteria, while girls with an abundance of Rikenellaceae had more fear than girls with a more balanced diversity of microbes.

To identify any connections between gut bacteria and temperament, mothers reported their child’s behavior using a questionnaire which measured 18 different traits that feed into three composite scales of emotional reactivity: Negative Affect, Surgency/Extraversion and Effortful Control. Scientists compared this information to the quantity of bacteria found in the toddler’s stool samples along with their diets.

“In the past, bacteria were cultured from samples in the lab, and scientists assumed that what grew was an accurate reflection of what was in the gut,” said Dr. Bailey.

“Now we can see that’s not the case. All of the predominant bacteria that we found in our study have been previously linked to either changes in behavior or immune response, so I think we are definitely on the right track.”

Research has shown that there are dramatic changes in gut microbes that take place during and after birth, as babies pick up bacteria from their mothers during labor and through breastfeeding. In fact, babies delivered through C-section will have different microbes than babies delivered vaginally.

“In this study, the associations between temperament and the gut microbiome that we saw weren’t due to differences in the diets of children. However, it is possible that effects of diet would emerge if we used a more detailed assessment.

“It is certainly possible that the types or quantities of food that children with different temperaments choose to eat affect their microbiome. ” said Dr. Christian, who also holds appointments in the departments of psychiatry, psychology and obstetrics/gynecology at Ohio State’s College of Medicine.

Both researchers say that parents shouldn’t try to change their child’s gut microbiome just yet. Scientists still don’t know what a healthy combination looks like, or what might influence its development.

“The bacterial community in my gut is going to look different than yours — but we are both healthy. The perfect microbiome will probably vary from person to person,” said Dr. Bailey.

The researchers are continuing to study how the gut microbiome impacts human health and behavior, recently publishing evidence that the babies of obese mothers have a different gut microbiome than babies of normal weight mothers.

Source: Ohio State University Center for Clinical and Translational Science

Gut Bacteria Impacts Toddlers’ Behavior, Particularly Boys