In a statement, i3S explains that scientists worked with a population sample that allowed them to identify associations between bacteria present in the gut and mouth and “substances produced by the body associated with impulsivity, emotional callousness, and antisocial behaviour.”

“The results show that certain gut and oral bacteria are associated with psychopathy traits in the community, suggesting that the body’s microorganisms may be related to processes linked to emotions and social behaviour,” says Carolina Costa, lead author of the study, which was conducted as part of her PhD in Biomedical Sciences at the Abel Salazar Institute of Biomedical Sciences (ICBAS).

The authors note that the study “does not demonstrate a cause-and-effect relationship” but contributes “to the growing evidence of a link between microorganisms in the gut and oral cavity and brain function, with a potential impact on emotions and behaviour.”

“We cannot state that bacteria cause psychopathy traits, but we observed a relationship between specific oral and gut bacterial profiles and specific behavioural characteristics,” observes Benedita Sampaio-Maia, the study’s coordinator and an i3S researcher.

According to the researchers, the work could pave the way “for the future identification of biological markers associated with mental health and the development of new intervention approaches based on diet, probiotics, or other ways of altering the body’s bacteria.”

Among the key findings, the team “identified associations between psychopathy traits and certain specific gut bacteria.”

“Researchers also observed differences in substances found in stool samples—specifically glucose (sugar) and taurine, a molecule produced by the body that plays a role in various brain and metabolic functions—both of which were associated with higher levels of the aforementioned traits,” the i3S reports.

The institute notes that “psychopathy involves a set of characteristics such as impulsivity, manipulation, a lack of empathy, and antisocial behaviour.”

“Although its origins involve both genetic and environmental factors, the biological mechanisms associated with these traits remain poorly understood,” they point out.

For this study, researchers recruited 200 Portuguese participants and assessed “psychopathic traits, empathy, and anxiety using psychological assessment scales.”

At the same time, they collected stool, saliva, and blood samples to study the bacteria present in the body and identify chemical substances potentially involved in gut-brain communication, the i3S explains.

The study was conducted in collaboration with researchers from the Faculty of Psychology and Educational Sciences at the University of Porto (FPCEUP), the Faculty of Dental Medicine at the University of Porto (FMDUP), and the University of Oxford.