Is our temperament influenced by our gut microbiota?

The gut microbiota of a two-month-and-a-half-old baby could be associated to their personality traits at six months, according to the results of an international study that confirm the hypothesis of a link between gut bacteria and our behavior.


The first months of life are key to the bacterial colonization in our gastrointestinal tract and the development of our nervous system. Since the brain and the gut communicate, we can assume that the composition of our gut microbiota plays a key role in the development of our temperament.

Bacterial diversity: a prerequisite for good emotional health

To test this hypothesis, a team of researchers analyzed the gut microbiota of 301 babies at the age of two months and a half and later assessed their temperament at the age of six months. They used a questionnaire filled in by parents to describe the way their child expresses and regulates their emotions. We know that three factors impact bacterial diversity of newborns–delivery mode (vaginal or c-section), diet (breast milk or formula) and mother’s age–, while bacterial abundance is only dependent on the type of diet. This study reveals that greater diversity is related to lesser negative emotionality (fear, sadness) and to lesser fear reactivity, which are two personality traits that are predictive of subsequent psychological disorders.

Is temperament dictated by bacteria?

The study also revealed several specific associations between some bacterial genera and newborns’ temperament. Abundance of Bifidobacterium and Streptococcus and low content of Atopobium seem to be, for instance, associated to positive emotionality, which is a predictive marker of extroverted nature and good emotional regulation. On the contrary, negative emotionality seems to be associated to the Erwinia, Rothia and Serratia bacteria; the latter also being correlated to prenatal maternal stress.  Fear reactivity proved to be specifically associated to an increased content of Peptinophilus and Atopobium bacteria. The authors point out that, even when their microbiota is the same, boys and girls do not have the same temperament, thus suggesting that the brain is differentially susceptible to the effects of gut microbiota based on gender.

Safeguarding mental health

Since personality traits can appear years before the development of psychological troubles, the authors believe that these results could have an impact on their early prevention in children. Provided, however, that a causal link is established, which is not the case in this study.



Aatsinki AK, Lahti L, Uusitupa HM et al. Gut microbiota composition is associated with temperament traits in infants. Brain Behav Immun. 2019 ;