Photo/Illutration Masako Myowa, right, a professor at Kyoto University, and Rinko Matsunaga, a researcher at Osaka University, in Kyoto’s Sakyo Ward on Sept. 4 (Rintaro Sakurai)

Human gut microbiota, the bacteria and other micro-organisms found in the digestive tract, can influence the emotions of young children, such as fear, anger and sadness, Japanese researchers said.

The team, including Kyoto University professor Masako Myowa, found that toddlers with more diversified microbiota tend to take on new challenges or act based on their interests.

It has already been found that gut microbiota is associated with the physical and mental health of adults.

The researchers focused on the composition and diversity of microbiota in toddlers because microbes become stable and more similar to those of adults when children are 3 to 5 years old.

The group also investigated the relationship between gut microbiota and development of the brain’s prefrontal cortex among children. The prefrontal cortex, which regulates actions and emotions and is associated with memories, develops rapidly in early ages.

The scientists surveyed the parents of 284 children who go to nursery schools or kindergartens by asking them 92 questions, based on international standards, about the toddlers’ temperaments over two weeks.

For each question, the parents had to give an evaluation on a scale from 1 to 7 about their children’s emotions and behavior.

The researchers gathered genetic information from the children’s feces as well as data on the diversity and composition of their gut microbiota.

The researchers found a higher prevalence of “negative” emotions, such as fear, anger, sadness and introvertedness, among children with fewer anti-inflammatory bacteria, more pro-inflammatory bacteria, and lower amounts of bacteria that produce butyrate, which regulates the environment in the gut.

These children were also more unlikely to take on new challenges or act based on their interests, the researchers said.

Children with more diversified gut microbiota had higher levels of impulsivity, such as quickly responding to stimulations, the study found.

Some overseas researchers have reported that negative temperaments, such as fear, anger, sadness and introvertedness, can lead to problematic behaviors and mental illness in children.

The Japanese research team will investigate if changing dietary habits in early childhood can enhance the composition and diversity of their gut microbiota.

They hope to develop ways to quickly and objectively evaluate children’s physical and mental health and find more effective ways to support children.

“What was important this time was that the research showed for the first time that imbalances in gut microbiota is associated with temperaments, which are used to measure mental health conditions,” said Rinko Matsunaga, a researcher at Osaka University who participated in the research.

She added, “I believe that evaluating the condition of gut microbiota of children, at least once, before they enter elementary school is effective in predicting physical and mental health.”

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