Gut Bacteria Are Linked to Depression

Wall Street Journal - Two studies find depression is associated with levels of some bacteria in the digestive tract

New research has bolstered a once-gutsy idea: Bugs in the digestive system may play a role in depression.

Two studies published Tuesday in the journal Nature Communications found a link between several types of bacteria in the gut and depressive symptoms. Trillions of microorganisms including bacteria, fungi and yeast live in the digestive tract. Research exploring whether they might affect an array of diseases has increased in recent years.

The new studies, conducted among thousands of people in two cities in the Netherlands, are among the largest to date demonstrating potential associations between gut microbiota and mental health .

"Ten years ago if you'd said there was something linking depression and the microbiome, you'd be carried out with a straitjacket," said Jos Bosch, an associate professor of psychology at the University of Amsterdam who co-wrote both studies. "Now absolutely, it's very clear there's a link."

Microorganisms in the gut have been linkedto diseases beyond depression including obesity, arthritis, diabetes and several cancers. Researchers said more work is necessary to confirm the associations and explore possible treatments and tests based on the microbes.

The new studies screened for depressive symptoms and analyzed the composition of microorganisms in people's gut using stool samples. One study, conducted in Rotterdam, involved about 1,000 European participants. The other involved over 3,000 people from different ethnic groups in Amsterdam. Results from the studies, which were adjusted for other variables such as age, smoking and body-mass index, partially corroborated each other, the researchers said.

"We were able to replicate our findings, making our results strong," said Robert Kraaij, a co-author of the studies and an assistant professor at Erasmus University Medical Center in Rotterdam.

Dr. Kraaij and his colleagues found that higher levels of bacteria, including those in the family Lachnospiraceae and the genus Eggerthella, were associated with more depressive symptoms. Lower levels of other bacteria, including those in the family Ruminococcaceae, were also linkedtodepression.

Scientists said the findings buttress research linking bacteriatodepression . "It's good to see these associations holding up in larger studies," said Gerard Clarke, a professor of neurobehavioral science at Ireland's University College Cork who wasn't involved in the new research.

Scientistsare exploring whether some gutbacteria produce or consume mood-regulating chemicals, such as serotonin, or chemicals that cause inflammation in the body, which research has linkedto depressive symptoms. Researchers involved in the new studies said some bacteria associated with depressionare known to produce substances that are thought to improve peoples' moods.

A 2019 study in Nature Microbiology suggested a link between bacteria that consume the chemical gamma-aminobutyric acid, sometimes referred to as a "downer" neurotransmitter, and lower depressive symptoms. Companies such as Holobiome are probing whether such bacteria can be used in oral medications to treat depression.

Researchers who conducted the studies in the Netherlands called their findings a preliminary step toward identifying biological indicators and therapies for depression. The precise relationship between depression and microbes in the gut couldn't be determined, they said. Depression can cause a person to eat less healthily , Dr. Bosch pointed out, which can lead to changes in the composition of microorganisms in the gut.

"Causality is a bit up in the air," he said.

Dr. Bosch and his colleagues said studies that track changes in participants over time are necessary, together with research in other countries and among more diverse groups. Sarkis Mazmanian, a microbiologist at the California Institute of Technology, said further research is needed to understand which bugs are associated with diseases such as depression and how they might contribute to the condition.

"The level of work and consistency in the findings linking microbiome and depression is quite robust," said Dr. Mazmanian, who wasn't involved in the recent studies. "It gives me reason to think that there's something going on here, likely more than a random association."

Write to Dominique Mosbergen at dominique.mosbergen@wsj.com

GutBacteriaAreLinkedtoDepression

Credit: By Dominique Mosbergen