Taking a daily probiotic supplement appears to improve anxiety in patients with chronic fatigue syndrome, new Canadian research suggests, a finding that might one day impact how depression and other mental disorders are treated.

The researchers, led by A. Venket Rao of the University of Toronto, found that giving patients with chronic fatigue syndrome (CFS) a probiotic for two months not only boosted so-called "good" bacteria in their stomachs, it also led to a significant decrease in their anxiety symptoms.

A probiotic is a dietary supplement, most often in pill or powder form, that contains live bacteria such as Lactobacillus or Bifidobacteria. These bacteria help maintain gut flora, microbes in the stomach that perform a variety of functions, including aiding digestion, boosting the immune system and warding off harmful bacteria.

"We were quite excited with the fact that these were positive results and we felt that probiotics truly have a role to play in the management of neurophysiological disorders such as anxiety, such as depression and other symptoms associated with that," Rao told CTV News.

"Rather than going into medications, which may result in side effects, it's a safe, it's a very easy way to manage problems such as that."

The findings are published in the journal BMC Gut Pathogens.

Patients who are diagnosed with CFS often experience a broad range of symptoms, the most significant being persistent fatigue. Nearly all CFS patients also experience neuropsychological problems, such as cognitive dysfunction, sleep disturbances, anxiety and depression. In fact, according to the researchers, about half of all CFS patients meet the diagnostic criteria for an anxiety disorder or major depressive disorder.

As well, CFS patients often complain of gastrointestinal problems and many are diagnosed with digestive disorders such as irritable bowel syndrome. Tests show that they often have lower levels of so-called "good" bacteria in their stomachs, which can regulate digestive activity.

All of this has led researchers to begin probing a link between gut bacteria and mental disorders and early findings suggest that bacteria levels may influence behaviour related to anxiety and depression.

Researchers believe that probiotics "crowd out" the more toxic stomach bacteria that are linked to an increase in depression and other mood disorders, study co-author Dr. Alison C. Bested told CTV News.

For this study, Rao, Bested and their team gave 39 CFS patients either three doses of Lactobacillus casei Shirota a day, or a placebo, for two months.

They found that 73 per cent of subjects taking the probiotic experienced an increase in levels of Lactobacillus and Bifidobacteria in the gut, which corresponded with a significant decrease in anxiety symptoms.

In the placebo group, only 37.5 per cent showed an increase in Bifidobacteria, while only 43.8 per cent showed an increase in Lactobacillus bacteria. The researchers found no statistically significant change in anxiety symptoms among this group.

According to Bested, Bifidobacteria appears to increase levels of tryptophan in the brain, a chemical that "helps people feel better."

Patients taking the probiotic also showed a marked improvement in their digestion, experiencing less bloating and gas and a reduction in inflammation.

The findings are "huge," Bested said.

"(Subjects) felt less anxious, they felt calmer, they felt better able to cope with their illness, they were sleeping better, had less heart palpitations and less symptoms of anxiety," she said.

"We were pleasantly surprised, that people who were taking probiotics were able to lower their anxiety."

Rao explained that the good bacteria produce "compounds that get to the brain and help the brain to manage problems associated with behavioural and mood problems, such as anxiety and depression."

He said the findings open "a door to a whole new field, and that is the relationship of gut micro flora, or gut bacteria, to many disorders - mental disorders being one of them. So it opens a door to many future research and applications in this area."

With a report from CTV medical specialist Avis Favaro and producer Elizabeth St. Philip