A new study suggests that probiotics, so-called "good" bacteria that aid in digestion, may also ease symptoms of depression. The finding adds to a growing body of evidence that what happens in the gut affects the brain.
Some 300 to 500 bacterial species inhabit the human gut, many aiding in digestion and the proper functioning of the gastrointestinal tract.
Experts say some of these bacteria produce proteins that communicate with the brain.
Your gut, your mood
The gut flora not only play a role in helping to orchestrate the neural responses that regulate digestion, scientists say, but evidence is emerging that gut bacteria can also affect a person's mood.
Premysl Bercik, a gastroenterologist at Ontario Canada's McMaster University, researches what he calls the microbiota-gut-brain axis, or the communication between the gut and the brain through the millions of bacteria that live in the gastrointestinal tract.
Bercik said between 40 and 90 percent of people with irritable bowel syndrome, a distressing intestinal disorder, also battle symptoms of anxiety and depression.
Research led by Bercik suggests the gut bacteria themselves may have an effect on mood.
In Bercik's pilot study of 44 patients with irritable bowel syndrome and mild to moderate anxiety or depression, half of the patients received a daily probiotic — a beneficial gut bacterium called Bifidobacterium longum — and the other half were given a placebo. The participants were followed for 10 weeks.
"What we found was that the patients that were treated with this probiotic bacterium improved their gut symptoms but, also surprisingly, decreased their depression scores," Bercik said. "That means their mood improved. And this was associated also with changes in the brain imaging."
Depression, anxiety improve
At the beginning of the study, the patients' levels of depression and anxiety were scored. The patients also underwent high-tech brain imaging to see which structures were activated in response to happy and sad images.
At six weeks, 64 percent of patients taking the probiotic had a decrease in their depression scores compared to 32 percent of the placebo patients.
A second round of imaging showed changes in multiple brain areas involved with mood control in the patients who felt better.
While the participants' gut symptoms improved, Bercik said it was not to a statistically significant degree, suggesting the probiotic may have improved their anxiety and depression independent of symptom relief.
Results of the study were published in the journal Gastroenterology.
More study needed
Bercik says larger studies are needed to confirm the findings.
"However, I think that it shows a great promise," he said. "I mean new treatments, not only for patients with functional bowel disorders like irritable bowel syndrome, but it may also offer some new treatments for patients with primary psychiatric disorders like depression or anxiety."
B. longum was developed by Nestle, a Swiss food and drink company, which funded the study. It is not yet commercially available.
However, Bercik says it's possible other probiotics found in the gut have the potential to improve mood. And he doesn’t stop there. Bercik says he envisions a form of personalized medicine using genome sequencing techniques to create microbiome profiles of individuals, which can be tweaked with oral probiotics for maximum health.