Finnish studies have found an association between gut microbiota and depression

Numerous discoveries have shown that the microbial status in the human gut is related to brain health and even mental illness, but what is the specific mechanism behind it has always been a mystery. This is also the reason why the "intestinal brain axis" has been ridiculed as "metaphysics" by the academic community. Recently, a sample of more than 6,000 people from Finland showed that some microbial characteristics in the gut may be associated with depression, and the conduction mechanism behind it is related to genes.

According to the "Science" magazine website reported on February 4 local time, Jack Gilbert, a microbial ecologist at the University of California, San Diego, commented that the finding came from a study on how heredity and diet affect the microbiome, "strongly demonstrating that this association may have important clinical significance." Gilbert was not involved in the Finnish study.

The study was led by Guillaume Méric, a microbial bioinformatician at the Baker Heart and Diabetes Institute in Finland. Rather than set out to look for gut microbes that cause depression, he directly retrieved information from Finland's large database of health and lifestyle research. The database is 40 years old and has been used to track the root causes of chronic diseases in Finns. Since 2002, the database has also recorded the genetic makeup, gut microbial status of 6,000 participants, and collected information about their diet, lifestyle, prescription drug use, and more.

Méric's research team combed through the data to look for clues as to how a person's diet and genetics affect the gut microbiome. Gilbert commented that few studies have examined all these factors in such detail. Méric reported this week in Nature Genetics that two points in the human genome appear to strongly influence which microbes are present in the gut. One contains a gene that digests lactose, and the other helps determine blood type. A second study in Nature Genetics on Feb. 4 also showed the same gene loci by analyzing the relationship between the genomes of 7,700 people in the Netherlands and the gut microbes.

Méric's team also explored which genetic variants might affect the abundance of gut microbes — and which of those variants were linked to 46 common diseases. The researchers report that the presence of two common bacteria that cause infections in hospitalized patients— Morganella and Kiebdiella— appears to cause depression in large numbers in the gut. A microbiological survey of 181 people who later developed depression by the research team found a significant increase in Morganella in their guts. The study is unique in that Méric's team linked an elevated level of bacteria to depression.

Mr. Mane bacteria

In 2008, researchers discovered a possible link between depression and inflammation: Depressed people had a stronger immune response to chemicals produced by Morganella and other gram-negative bacteria in their gut. As a result, Gilbert said, the latest study appears to "further demonstrate" that inflammation caused by gut microbes affects people's mood.

But the field is still in its infancy, says Gerald Clark, a microbiome researcher at University Cork, that because there are many forms of depression, there are many ways in which microbes may influence the disease. The "holy grail," he said, is about finding out the missing microbes that can be used as a complement. But it's unclear how to eliminate Morganella from the gut to relieve symptoms, which is more challenging.