Probiotics May Ease Depression Symptoms According to Study

Probiotics alone or combined with pre-biotics may help ease the symptoms of patients with depression, according to a review of existing studies.

The authors of the paper, published in the journal BMJ Nutrition, Prevention, and Health, said there is a "highly developed" two-way relationship between the central nervous system—comprised of the the brain and the spinal cord—and the gastrointestinal tract. That includes bacteria which populate the gut, called the microbiota. This link is known as the gut-brain axis.

By reviewing seven existing studies, the researchers set out to consolidate what is known about mental health and probiotics (which are thought to positively influence the microbiota and their collective genetic material) and prebiotics (which help the germs grow). The studies assessed only looked at people diagnosed with depression or depression and anxiety, and none which fit their criteria looked at anxiety primarily. A total of 12 probiotic strains were explored in the small studies, which all involved less than 100 people.

The studies showed probiotics alone or combined with pre-biotics appeared to improve the symptoms and or biochemical measures relevant to anxiety and depression, regardless of the probiotic.

"Our results affirm that pre/probiotic therapy warrants further investigation," the authors wrote.

Co-author Sanjay Noonan of the Brighton and Sussex Medical School in the U.K., told Newsweek the paper should be approached with caution as it doesn't prove anything in and of itself. The purpose of the research was to gain a more coherent picture of the present body of research relating to pre and probiotics and mental health, and to signpost how current research is flawed and how future studies could be improved.

Asked what readers take away from the study in terms of their own habits and behaviors, Noonan said he would "not suggest in any way that this research should try to be implemented by individuals." Noonan said he wouldn't want to make generalized statements about diet to people with anxiety and depression "in the absence of much more clinical data about those people nor without understanding the extent to which diet is important in their particular case at that particular time."

Clinicians might, however, want to read the paper "to recognize that conditions such as depression and anxiety are highly complex, altered by the idiosyncrasies of individual patients, the personal and social contexts in which they live and that any particular approach taken should be highly adaptive," he said.

Professor John Cryan, a neuroscientist at University College Cork who did not work on the paper, told Newsweek there has been increasing interest in the role of the microbiome on the brain and behavior in recent years. His team in Cork have, for instance, coined the phrase "psychobiotic" to describe attempts to improve mental health via the microbiome.

Cryan said the review was "well-conducted" but had limitations, largely related to how new the field is. "There is a strong potential for publication bias in the field with very few negative randomized controlled studies published," he said.

Cryan said the review was unable to identify what it is about specific strains that made them beneficial. He said that a probiotic is by definition a microorganism that, when taken in an adequate amount, confers a health benefit—"and there is a tendency in the field to 'lump' all commercially available strains into the same category independent of the level of evidence there is."

As the review highlights, said Cryan, there is a "great need" for studies on different "psychobiotics" strains and diets both as a standalone or complementary treatments for anxiety and depression, where participants are followed up periodically.

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A stock image shows a woman having a therapy session. Researchers have reviewed existing evidence on the gut-brain axis and pre and probiotics. Getty