A study published in Translational Psychiatry reports associations between the gut and oral microbiome and subclinical psychopathic traits among the general public. Led by Carolina F.F.A. Costa, researchers from the University of Porto and the University of Oxford recruited 200 adult volunteers in Portugal. Participants without recent antibiotic exposure completed extensive self‑report questionnaires assessing psychopathy, empathy and anxiety. Using a computer algorithm, volunteers were grouped into four categories reflecting different levels of psychopathy and anxiety; those with higher psychopathic traits tended to report lower empathy.
The team collected stool, saliva and blood samples to map the microbiomes and to analyse metabolites. DNA sequencing identified gut and oral bacteria, while metabolite profiling measured small molecules produced during digestion and microbial processing.
Diversity of the microbiome did not differ across the four groups after adjusting for age. But certain bacteria showed associations with personality. In the gut, higher levels of Allisonella, Prevotella and Cloacibacillus evryensis were linked to higher psychopathy scores; in the mouth, Treponema vincentii was less abundant in individuals with higher psychopathy scores.
Some bacteria have biological roles that could influence the brain. Allisonella produces histamine, a chemical that triggers immune responses and inflammation; Cloacibacillus evryensis has the genetic potential to produce gamma-aminobutyric acid in the gut, an inhibitory signal in the central nervous system; Prevotella has been previously associated with differences in how the brain processes emotional and sensory stimuli.
Among more than 200 metabolites examined in stool and blood, two stood out: glucose and taurine, both elevated in the group with high psychopathy and anxiety. Higher fecal glucose and taurine levels correlated with traits such as antisociality and interpersonal manipulation. Glucose serves as the primary energy source, and the digestive tract contains sensors that detect glucose and send metabolic updates to the brain.
Taurine is an amino acid involved in brain development and anxiety regulation; it normally binds to bile acids to aid fat digestion, with gut bacteria eventually separating taurine from bile. Excess free taurine in stool can indicate nutrient absorption issues or overgrowth of certain bacteria.
When researchers cross-referenced bacterial data with metabolite data, higher levels of Allisonella in the gut predicted higher amounts of both glucose and taurine. This suggests that specific gut bacteria might be altering energy metabolism in ways that relate to personality expression.
The researchers note several caveats. The study’s cross‑sectional design cannot prove that gut bacteria cause psychopathic traits; it remains possible that the behaviours associated with psychopathy influence diet or physiological stress responses and, in turn, the microbiome. The participants were volunteers from the general community rather than individuals with clinical diagnoses, and the psychological data came from self‑reported surveys, which can be biased.
The study, titled “Gut and oral microbiota composition is associated with psychopathic personality: a cross‑sectional study,” was authored by Carolina F.F.A. Costa, Daniel Radford-Smith, Alexandre R.T. Figueiredo, Rita C.M. Ribeiro, Sofia Pinto, Fay Probert, Renata Barros, Paula Serrão, Luisa Barreiros, Marcela A. Segundo, Daniel C. Anthony, Fernando Barbosa, Philip W.J. Burnet, and Benedita Sampaio-Maia.
