Intestinal flora affects mental health? Useful research or nonsense?

Once upon a time, the idea that gut bacteria affect mental health is considered whimsical, but today it has become an important research topic.

Just a decade ago, the idea that gut microbes affected the brain was often reprimanded as a nonsense – it will never happen again.

The association between the central nervous system and the gut microbiota has become an important research direction, attracting widespread public attention, and relevant reports are frequently reported. But how does this "gut-brain axis" work? The mechanisms by which microbes shape brain functions, such as memory and social behavior, and the ways in which they affect depression and neurodegenerative diseases are slightly weak and often controversial.

The association between the central nervous system and countless human intestinal microbes has become an important research topic and public focus.

Current research in this area can only show that certain intestinal bacteria and their metabolites are associated with neurological symptoms. But the relationship is not equal to causality. Moreover, many studies use animal models that do not accurately reflect human traits or behavior. In addition, human studies have been limited: the number of subjects is generally relatively small, and a number of confounding factors (such as abnormal diets, antibiotics, and antidepressants) that may affect the microbiota may not be controlled.

A recent study published in Nature-Microbiology gives answers to some of these questions (M. Valles-Colomer et al. Nature Microbiol. https://doi.org/10.1038/s41564-018-0337-x 2019). The authors used DNA sequencing to analyze the fecal flora of more than 1,000 participants in the Belgian Flemish Gut Flora Project, and analyzed the different microbial species and the quality of life and depression of the subjects. The incidence of morbidity was correlated - the quality of life and the incidence of depression were derived from the self-reported reports of the subjects and the diagnosis of the doctors.

The researchers confirmed this finding through an independent cohort of 1,063 individuals in the LifeLines DEEP project in the Netherlands. Finally, by mining the data, they generated a catalog describing the ability of these flora to make or degrade molecules that interact with the human central system.

As a result, it was found that Coprococcus and Dialister bacteria were reduced in patients with depression. They also observed a positive correlation between the quality of life and the potential ability of gut microbes to form a derivative of the neurotransmitter dopamine, 3,4-dihydroxybenzoic acid. The above findings are one of the most powerful evidences that the human intestinal flora can affect mental health.

However, these are still only related relationships, not causal relationships. Researchers know that gut microbiota can generate or stimulate the production of neurotransmitters and neuroactive compounds such as serotonin, GABA and dopamine, which can regulate bacterial growth.

At present, the challenge for researchers is to determine whether these microbial source molecules interact with the central nervous system of the human body, and if so, by what means, and whether this interaction will change a person's behavior or suffering. Disease risk. At least for now, it’s wise to explore these issues, not a nonsense.

Source: Nature Natural Science Research