Social phobia is all in the head... and in the microbiota

We know that the gut and the brain are in constant dialog. Studies suggest that the “ microbiota-gut-brain axis ” plays an important role in anxiety, stress, major depressive disorder and autism.

What about the microbiota of people with social phobia? Does it also display characteristics suggesting it plays a role in the disease via communication with the brain?

Until now, a lack of data has made it difficult to answer this question. However, a study by a team of Irish researchers from University College Cork (UCC) suggests that this may indeed be the case.

The scientists enrolled 31 people diagnosed with social phobia, together with 18 controls not suffering from the condition. They collected the participants’ stools to analyze and compare the composition of their microbiota. What did the analyses show?

^{Sources. (sidenote: Fehm L, Pelissolo A, et al. Size and burden of social phobia in Europe. Eur Neuropsychopharmacol. 2005;15:453–62.
Kessler RC, Petukhova M, et al. Twelvemonth and lifetime prevalence and lifetime morbid risk of anxiety and mood disorders in the United States. Int J Methods Psychiatr Res. 2012;21:169–84. )}

Significant differences in bacterial composition

Compared to the control group, the microbiota of the “social phobia” group contained more Anaeromassilibacillus. Several studies have shown this bacterial genus to be implicated in autism and depression, two disorders that share physiological processes with social phobia.

Their microbiota also contained more Gordonibacter, a bacterial genus that can produce the metabolite urolithin from the breakdown of polyphenols, which studies show has an impact on mental health.

The social phobia group also had lower levels of Parasutterella excrementihominis. Several studies have shown this bacterium to be less abundant in people suffering from autism spectrum disorders, but also in those with a high body mass index (sidenote: Indice de masse corporelle Rapport du poids en kg sur le carré de la taille en m2 )  or sugar intake, which is common in people suffering from phobias, including those in the study.

Another notable difference was that their microbiota showed a significant enrichment in a metabolic pathway for aspartate degradation via a specific protein. According to the authors’ analysis, this protein is similar to another involved in the metabolism of tryptophan, one of the messengers involved in the functioning of the gut-brain axis.

Towards new treatments and biomarkers

According to the researchers, this small study is highly important and will lay the foundations for larger-scale studies to confirm the involvement of the gut-brain axis and specific bacteria in social anxiety disorder.