Gut-brain axis expanded: Regulating gut bacteria could ease anxiety, reveals research

22 May 2019 --- People who experience anxiety symptoms might be helped by taking steps to regulate the microorganisms in their gut using probiotic foods and supplements, suggests a review of studies. Supporting the expanding clinical evidence of the gut-brain axis notion, the meta analysis has been published in the journal General Psychiatry and points to a potentially useful link between gut bacteria and mental disorders.

Increasingly, research has indicated that gut microbiota – the trillions of microorganisms in the gut which perform important functions in the immune system and metabolism by providing essential inflammatory mediators, nutrients and vitamins – can help regulate brain function. 

Earlier this year, researchers established a correlation between depression and a group of neurotransmitter-producing bacteria found in the human gut. Interestingly, an inverse relationship between specific gut bacteria and brain activity in areas connected to depression were identified in the animal study, which further supports the gut-brain axis concept – the biochemical signaling that takes place between the gastrointestinal tract and the central nervous system.

There is also mounting evidence linking imbalances in the microbial species that make up the gut microbiome to a number of health problems including allergies, autoimmune disorders and psychiatric mood disorders. Probiotics have even been flagged as a potential avenue of treatment to alleviate bipolar and other psychiatric mood disorders by a Baltimore Sheppard Pratt Health System study.

And now, following this review of studies carried out by a team of researchers from the Shanghai Mental Health Center at Shanghai Jiao Tong University School of Medicine, there are suggestions that mental disorders could be treated by regulating the intestinal microbiota. However, to date, there is no specific evidence to support this.

What happened in the review?
The researchers reviewed 21 studies in total concerning 1,503 people collectively. Of the 21 studies, 14 had chosen probiotics as interventions to regulate intestinal microbiota (IRIFs), and seven chose non-probiotic methods, such as adjusting daily diets.

Seven of the probiotic supplements within the analysis contained only one kind of probiotic, while two of the studies focused on a product containing two kinds of probiotics. The supplements used in the other five studies included at least three kinds.

Overall, 11 of the 21 studies showed a positive effect on anxiety symptoms by regulating intestinal microbiota. This means that more than half (52 percent) of the studies showed this approach to be effective. However, some studies that had used this approach did not validate this outcome.

More than a third (36 percent) of the 14 studies that had used probiotics as the intervention, found them to be effective in reducing anxiety symptoms, while six of the remaining seven studies that had used non-probiotics as interventions found those to be effective. This represents an 86 percent rate of effectiveness.

Some studies had used both the IRIF approach and treatment as usual. In the five studies that used treatment as usual and IRIF as interventions, only studies that had conducted non-probiotic ways yielded positive results, which showed a reduction in anxiety symptoms.

The review also shows that non-probiotic interventions were more effective in the studies that used IRIF alone. In those studies only using IRIF, 80 percent were effective when using non-probiotic interventions. Forty-five percent were found to be effective when using probiotic ways.

Changing diet could have more of an impact on gut bacteria growth than introducing specific types of bacteria in a probiotic supplement, the authors note. 

In addition, some studies had involved introducing different types of probiotics. The researchers note that these could have fought against each other to work effectively. However, many of the intervention times used might have been too short to significantly increase the abundance of imported bacteria.

The researchers also claim the overall quality of the 21 studies was high, although they do recognize this was a purely observational review study, which cannot establish cause. The authors also acknowledge the differences in study design, subjects, interventions and measurements, making the data unsuitable for further analysis.

In conclusion, they note that in addition to the use of psychiatric drugs for anxiety treatment, regulating intestinal flora as a way of alleviating symptoms could also be considered.