A new study out of Oxford University is suggesting there is a strong link between individual personality traits and gut microbiome composition. The research does not claim gut bacteria directly determines a person’s personality, but instead reveals a distinct and perhaps bi-directional, association between behavior and the microbiome.

“There has been growing research linking the gut microbiome to the brain and behavior, known as the microbiome–gut–brain axis,” says the study’s author, Katerina Johnson. “Most research has been conducted in animals, whilst studies in humans have focused on the role of the gut microbiome in neuropsychiatric conditions. In contrast, my key interest was to look in the general population to see how variation in the types of bacteria living in the gut may be related to personality.”

The new research grew out of a number of recent studies linking gut bacteria with autism. Not only have specific gut bacteria been associated with autism, but fecal transplants have been found to influence autistic behaviors in both animal and human studies. Johnson’s study hypothesized that if certain types of gut bacteria had the capacity to influence autistic behaviors, then those same bacteria may be linked with certain basic personality traits such as sociability or neuroticism.

The study’s conclusions did indeed back up the initial hypothesis. A number of species of gut bacteria previously linked with autism also correlated with sociability traits in healthy adults. Individuals with high sociability presented abundant levels of Akkermansia, Lactococcus and Oscillospira bacteria. All three genera have been identified in lower than average levels in autistic subjects.

On the other hand, Desulfovibrio and Sutterella were two genera found in high levels in those less sociable individuals with tendencies toward introversion. Again, both genera of bacteria have been identified in abundance in subject with autism.

More neurotic personalities could be detected by correlating lower levels of Streptococcus and Corynebacterium bacteria. Corynebacterium in particular has been linked to depression in animal models.

In general, the study detected a consistent correlation between gut microbiome diversity and individual sociability. So essentially, the larger a person’s social network, the more diverse their gut microbiome. On this point Johnson hypothesizes a certain degree of social transmission of some micro-organisms may be at play.

“The relationship between gut microbiome diversity and human social networks has not previously been explored but the positive relationship found here suggests that social interactions may also influence the microbiota of human societies,” Johnson writes in the study. “Interestingly, a study of gut microbiome composition and temperament in infants reported an association between gut microbiome diversity and sociability.”

Other more general, and somewhat unsurprising, findings in the study suggest greater microbiome diversity is associated with frequent international travel. And, greater diversity was also linked with diets high in fermented and prebiotic foods.

Interestingly, probiotics taken in the form of supplements correlated with decreased microbiome diversity. Johnson points out this unexpected correlation is most likely due to the tendency of persons with gut health problems to be taking probiotic supplements.

Ultimately, the study does not intend to imply direct causation between gut bacteria and personality traits, but instead Johnson stresses the relationships seen here are most likely bi-directional. As she notes in the study’s conclusion, “gut bacteria can affect behavior and behavior can in turn influence the composition of the gut microbiome.”

Still, this fundamental, almost symbiotic relationship, between a person’s microbiome and their overall behavior or well-being is what Johnson suggests is the takeaway from the comprehensive study. If we accept a growing body of research associating extreme traits seen in psychiatric disorders with gut bacteria, then it is not unreasonable to link moderate behavioral variations in general healthy adults with the microbiome. However, it certainly isn’t as simple as a single bacterial species causing a person to exhibit an extroverted personality.

“Our modern-day living may provide a perfect storm for dysbiosis of the gut,” says Johnson. “We lead stressful lives with fewer social interactions and less time spent with nature, our diets are typically deficient in fibre, we inhabit oversanitized environments and are dependent on antibiotic treatments. All these factors can influence the gut microbiome and so may be affecting our behavior and psychological well-being in currently unknown ways.”

The new study was published in the Human Microbiome Journal.

Source: Oxford University