New study suggests gut microbiota can influence brain structure

In a study recently published in the Journal of Affective Disorders, researchers have found evidence suggesting that certain types of gut bacteria may influence the thickness of the brain’s cortex. The study identifies specific bacteria within the orders Lactobacillales and Bacillales that are potentially associated with changes in brain structure.

Our gut is teeming with microorganisms that influence various aspects of our health, from metabolism and immunity to our risk for diseases. Recently, scientists have begun to explore how these microbes might also impact the brain. This interaction between the gut and the brain is often referred to as the microbiota-gut-brain axis. Prior research has shown that changes in the composition of gut bacteria are linked to a variety of brain functions and disorders, including cognitive abilities and mental health conditions.

However, the mechanisms behind this influence are not fully understood. Traditional studies have faced challenges such as small sample sizes and confounding factors, which can obscure true effects.

In their new study, researchers at Capital Medical University in Beijing aimed to provide clearer evidence using a technique called Mendelian randomization, which helps to infer causal relationships from genetic data. This technique leverages genetic variations as natural experiments to explore the influence of modifiable risk factors on health outcomes.

The researchers used genetic data from large public health databases, analyzing genes related to the presence of certain gut bacteria and their potential impact on the thickness of various brain regions. They focused on two groups of bacteria, Bacillales and Lactobacillales, known for their prevalent roles in human health. The study involved over 51,000 participants primarily of European descent.

The researchers identified a statistically significant association between the abundance of Bacillales and Lactobacillales and the thickness of the cerebral cortex. This association was consistent across global measures of cortical thickness and notably in specific brain regions that are crucial for various cognitive and sensory functions.

For Bacillales, an increase in cortical thickness was observed in brain regions such as the fusiform, insula, rostral anterior cingulate, and supramarginal areas. Lactobacillales showed a similar impact, particularly increasing thickness in the fusiform and supramarginal regions.

These regions are involved in processes such as visual processing, emotional regulation, sensory perception, and cognitive control, suggesting that the influence of these bacteria could extend to these fundamental neural functions.

But how would gut microbiota influence brain structure? The researchers noted that gut bacteria affect metabolic functions in the liver, influencing the synthesis and breakdown of fatty acids which, when altered, can cross the blood-brain barrier and impact neuronal activity. Additionally, gut microbes produce a range of metabolites and hormones that are crucial for the gut-brain signaling system.

Despite its innovative approach, the study has limitations. The findings are based on genetic data that predict bacterial levels rather than direct measurements, which might not capture the dynamic nature of gut microbiota. Additionally, the study’s population was mainly of European ancestry, which might limit the generalizability of the results to other ethnic groups.

Nevertheless, the findings suggest that the microbiota-gut-brain axis could be a viable target for therapeutic interventions in neurological and psychiatric disorders. The researchers call for further studies with diverse populations and direct measures of gut microbiota to confirm these findings. They also suggest that future research should explore the mechanisms through which these bacteria influence brain structure.

“Overall, our study supports the view that an interventional approach using probiotic strains (including order Bacillales and Lactobacillales), prebiotics and potentially fecal microbiota transplantation therapy may be an effective initiative to improve brain function, taking into account cost, feasibility and patient compliance,” the researchers said.

“By modulating the gut microbiota composition and regulating the gut-brain axis interaction, these interventions hold potential therapeutic value for various neurologic disorders. However, further clinical research is needed to verify the safety and efficacy of these interventions and to determine specific details and applicability of the optimal treatment protocols.”

The study, “Association of gut microbiota with cerebral cortical thickness: A Mendelian randomization study,” was authored by Lubo Shi, Xiaoduo Liu Shutian Zhang, and Anni Zhou.