Many of us instinctively feel the connection between the gut and the brain. That link and how the range of bacteria found in our digestive tract – our microbiome – can help treat mental illness has become an area of interest for researchers in recent years.
A recent review of medical literature has suggested that probiotics – foods or supplements that contain microbes that are believed to exert a positive influence on the gut – may help ease depression.
“This is good quality research, but it is a review of relatively preliminary data,” Allan Young, professor of mood disorders at the Institute of Psychiatry, Psychology & Neuroscience, King̵
“Although this systematic review of the research literature supports the notion that pre- and probiotics may be helpful for people with anxiety and depression, more research is needed. These data make it possible to do larger studies,” said Young, who was not involved in the review .
Researchers from the University of Brighton and Croydon University Hospital in the UK looked at 71 studies published between 2003 and 2019 that looked at how probiotics and prebiotics, compounds that help probiotics flourish, can help adults with depression and / or anxiety disorders.
Only seven were considered sufficiently robust to be included in the systematic review, but all showed “significant improvements” when measuring the efficacy of taking pre / probiotics compared to no treatment or placebo. Although probiotic supplements either alone or in combination with prebiotics may be linked to measurable reductions in depression, the possible contribution to reducing anxiety was not yet clear, the study said.
The researchers said their review had several warnings: None of the included studies lasted very long; and the number of participants in each was small.
This made it difficult to draw any firm conclusions about the overall effects, how long they lasted and whether there may be unwanted side effects associated with long-term use, they said.
David Curtis, a retired consultant psychiatrist and honorary professor at University College London, said probiotics were unlikely to affect the mood.
“Although these published studies claim to show some benefits of probiotics for depression, we have no idea there were other studies that showed no effect that were not published,” he told SMC.
“People with depression should seek medical help and not try to treat themselves with dietary supplements, which are of no avail.”
First, probiotics can help reduce the production of inflammatory chemicals, such as cytokines, or they can help control the action of tryptophan, a chemical thought that is important in the gut brain axis in psychiatric disorders.
Second, people with depression often have other underlying conditions, such as impaired insulin production and irritable bowel syndrome, and probiotics can affect how a person experiences depression by relieving these conditions.
However, the case for the use of probiotics in the treatment of digestive disorders is not clear.
“We are still learning about the many complex communication pathways between the brain and the gut. It is likely that microbiome-directed therapies can improve aspects of depression and anxiety by alleviating an individual’s GI,” said Dr. Geoffrey Preidis, spokesman for the association and a pediatric gastroenterologist at Baylor College of Medicine and Texas Children’s Hospital.
“AGA’s review of the current evidence base did not find enough evidence to recommend probiotics for IBS right now. However, future clinical studies will address this knowledge gap, so we must continue to evaluate the rapidly changing evidence in this exciting field, “he said via email.
Probiotics have become more popular as researchers have learned more about the role of our gut bacteria, or microbiome, in our gastrointestinal health, with probiotics that promise an effective way to change the microbiome to our advantage.
The studies in the review looked at 12 probiotic strains, mainly Lactobacillus acidophilus, Lactobacillus casei and Bifidobacterium bifidum. One study looked at combined pre-probiotic therapy, while one looked at prebiotic therapy by itself.
John Cryan, professor and chair of the Department of Anatomy and Neuroscience and principal investigator at the University College Cork’s Alimentary Pharmabiotic Center, said it was important to identify which strains had the effect.
“We know that tribes really mean something, and this review can’t identify what it is about specific tribes that make them positive,” he told SMC.
“As this review highlights, there is a great need for longitudinal studies for various psychobiotic strains and diets, either as stand-alone or as complementary therapies for anxiety and depression.”