A new study from Oxford University, published in the journal Human Microbiome, has linked gut bacteria strains and diversity with people’s personalities.
That might seem outlandish; after all, our personalities define us. As researcher Katerina Johnson writes, they “shape our world”, permeating relationships, hobbies, behaviours, social interactions, working life and how we cope with stressors.
But as links have been found between gut bacteria and autism – a condition typified by impaired social function – and other psychiatric conditions, Johnson thought it was plausible to explore whether they vary with human personalities more generally.
Indeed, animal studies exploring the microbiota-gut-brain axis have shown that gut bacteria can impact the stress response, anxiety and depressive behaviours, communication and social interactions.
Even more intriguingly, faecal transplants have transferred depressive symptoms from humans to mice, and improved psychiatric symptoms in humans with gastrointestinal disease.
To investigate a possible link with personality more broadly, the new study analysed faecal samples from more than 600 people– mostly from North America – along with personality, health and lifestyle, diet and sociodemographic information.
Controlling for these confounding factors, results showed that more sociable people had greater gut microbiome diversity, while those with higher anxiety or stress had less.
This could be attributed to more sharing of bacteria between people with larger social networks. It follows, then, that travellers also had a more assorted gut bacteria while unemployed people had lower diversity.
The abundance of Lactococcus and Oscillospira in socialites corresponds with reduced levels found previously in children with autism. Conversely, Desulfovibrio and Sutterella, which proliferate in autism, were also higher in less sociable people.
People with neurotic tendencies had less Streptococcus and Corynebacterium, the latter bacteria previously found to drop in mice with stress-induced depression.
Results were not all consistent with other research, though, and Johnson stresses it is a correlational study that needs further exploration.
Notably, the findings aligned with other observations about gut microbiome diversity.
For instance, more adventurous foodies and people who ate foods high in natural probiotics (such as fermented cheese, sauerkraut, kimchi) and prebiotics (such as banana, legumes, whole grains, asparagus, onion, leek) had greater gut diversity.
On the other hand, people who had been formula-fed as infants had lower gut diversity.
“This is the first time this has been investigated in adults,” says Johnson, “and the results suggest that infant nutrition may have long-term consequences for gut health.”
Although many more questions remain, she notes that the study adds another dimension to the impact of bacteria-depleting lifestyles, that include stress, unhealthy diets, excessive sanitation and antibiotics, on health and wellbeing.
“Our modern-day living may provide a perfect storm for dysbiosis of the gut”, she says.
“All these factors can influence the gut microbiome and so may be affecting our behaviour and psychological wellbeing in currently unknown ways.”
