Scientists are taking a closer look at how microorganisms living in the gastrointestinal system impact mental health. A new study suggests that bacteria in the gut microbiome is linked to bipolar disorder.

The research, published in the Journal of Psychiatric Research, suggests that the microbial population of the gastrointestinal tract plays a role in bipolar disorder.

“Recent studies have supported the gut microbiome, the collection of microbes in the digestive tract, as important for mental health,” the study’s corresponding author, Simon J. Evans of the University of Michigan, told PsyPost. “There are effects on brain development from early influence of the gut microbiome as well as effects in adults to modulate behavior and mood. We leveraged these studies to test the hypothesis that the gut microbiome may be different in individuals with bipolar disorder compared to controls; and further that specific microbiome profiles might associate with burden of disease in patients with bipolar disorder.”

By analyzing stool samples, the researchers compared the gut microbiome of 115 individuals with bipolar disorder to a control group of 64 healthy individuals.

They found that the gut bacteria of bipolar and control subjects were significantly different. In particular, individuals with bipolar disorder had less of a beneficial human gut microbe known as Faecalibacterium. Reduced levels of Faecalibacterium were associated with more severe bipolar symptoms.

“There is growing evidence for a role of the gut microbiome in mental health and one of the major factors that influences the gut microbiome is diet,” Evans explained to PsyPost. “The bottom line is that diet matters for mental health, consistent with previous work we have been doing for several years.”

But the fact that most bipolar individuals in the study were taking more than one psychiatric medication could complicate things.

“We don’t yet understand what roles psychiatric medications play in influencing the gut microbiome and our results might be secondary to drug treatment,” Evans said. “We also don’t yet understand how medications interact with dietary nutrients to control the complement of the gut microbiome.”

“We are currently addressing some of the next questions with a dietary clinical trial in bipolar illness. We are testing the hypothesis that a diet high in healthy fats will improve the gut microbiome and lessen the burden of disease for bipolar patients.”

The study, “The gut microbiome composition associates with bipolar disorder and illness severity“, was also co-authored by Christine M. Bassis, Robert Hein, Shervin Assari, Stephanie A. Flowers, Marisa B. Kelly, Vince B. Young, Vicky E. Ellingrod, and Melvin G. McInnis.