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New Study Finds That Gut Bacteria Could Dictate Toddler Temperament

Last updated June 26, 2015

Approved by: Krish Tangella MD, MBA, FCAP

Researchers at Ohio State University studied the gut bacteria of 77 children 18-27 months. Through stool sample analysis and questionnaires given to mothers, researchers were able to draw some conclusions about how gut microbes of children can affect their temperament.

The gut harbors over 400 different varieties of bacteria, known as the gut microbiome, and their composition can expose people to physical and mental problems (ex. obesity and anxiety). Children’s gut microbiomes can predispose them to developing such problems when they are older. Researchers at Ohio State University studied the gut bacteria of 77 children 18-27 months. Through stool sample analysis and questionnaires given to mothers, researchers were able to draw some conclusions about how gut microbes of children can affect their temperament. Further understanding of this field will allow researchers to determine how to decrease children’s chances of developing chronic illnesses that are linked to imbalances in the gut (ex. Crohn’s disease). However, there may not be a perfect gut microbe composition. As co-author Dr. Bailey stated, “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.”

The human gut, often called the “second brain” and the only organ to have its own nervous system, contributes to mood and behavior. Both adult and toddler temperaments are reported to be influenced by the bacteria they harbor in their gut. Researchers at Ohio State University studied the gastrointestinal tracts of children around two years old. They found correlations between the abundance and diversity of certain bacterial strains and the expression of particular behaviors. Other factors (ex. diet, method of childbirth, breastfeeding) were also taken into account, as these are known to influence a child’s microflora. Dr. Christian, a researcher at the Behavioral Medicine Research at Ohio State, explained this phenomenon, “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…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”. The researchers studied children around two years of age because their microbiota is indicative of their gut microbial population when they became adults.

Experimental Setup

  • Stool samples of 77 girls and boys from the Columbus, Ohio community were analyzed for bacteria; the type of bacteria and quality were measured via DNA sequence analysis.
  • Children excluded from the study: those with major health conditions, delayed development, or toilet trained, which hindered collection of the stool
  • Mothers assessed their child’s behavior by completing a questionnaire measuring 18 different traits that were narrowed down to three groups: Negative Affect, Surgency/Extraversion (positive trait), and Effortful Control (adaptability).
  • The demographic characteristics included in the questionnaire included:
    • The mother’s age, race, and marital status
    • The child’s age, race, sex, duration of breastfeeding, formula use, when whole foods were introduced to the child’s diet, frequency of each food type
  • The samples were collected by the mother within a week of when the questionnaire was completed.


  • The researchers compared boys and girls, as had been done in other studies; the questionnaire ratings differed based on the child’s sex:
    • Girls rated higher in Effortful Control while boys in Surgency/Extraversion were consistent with previous studies.
  • Children with a more genetically diverse microflora frequently demonstrated positive mood, curiosity, sociability, and impulsivity.
  • The study found few differences in abundance and type of bacteria between boys and girls. However:
    • An abundance of certain microbes was seen to be associated with extroverted personality traits in boys.
    • Girls demonstrated a less consistent association of temperament and gut microbiome. In some cases, the researchers observed behaviors like self-restraint, cuddliness and focused attention on girls with low microbiome diversity. The researchers also noted that an abundance of certain bacteria in girls were seen to be associated with fear compared to the girls with more balanced microbe diversity.

The study was only designed to find correlations, thus other studies need to be conducted to address causal pathways between gut microbiome and behavior. According to this study, the correlation between temperament and gut microbiome was not due to differences in the diet. Perhaps the impact of the diet was missed because it was not assessed in much detail. Co-author Dr. Bailey states, “There is definitely communication between bacteria in the gut and the brain, but we don't know which one starts the conversation…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."

Written by Monique Richards

References and Information Sources used for the Article:

Reviewed and Approved by a member of the DoveMed Editorial Board
First uploaded: June 26, 2015
Last updated: June 26, 2015