Several new studies have highlighted the connection between the community of microbes in the human gastrointestinal tract, and mental health. The gut microbiome seems to have a direct link to the brain through the vagus nerve, and can regulate neurotransmitters. Research has suggested that the gut microbiome could have an influence on a variety of disorders that are related to the brain, including anxiety, addiction, depression, some neurodegenerative diseases such as Parkinson’s, and even insomnia.
In a new review published in Nature Mental Health, researchers have summarized some of what we know about these connections. The report noted that there is strong evidence from animal models that shows a causal connection between the gut microbiome and changes in behavior, stress, and brain chemistry.
There are major changes in the gut microbiome that have been linked to depression, schizophrenia, and other mental disorders.
The gut microbiome also presents a potential treatment avenue for some conditions, since various trials involving dietary changes, probiotics, or fecal microbiota transplants have led to improvements in anxiety and mood disorders. There are also psychiatric medications that alter the microbiome, further indicating a link between the gut and brain.
One primary area of study is whether changes in the gut microbiome can cause mental health issues, or if mental problems precede changes in the gut microbiome. This situation may also be different for different people or disorders. More research will be needed to fully understand how the gut-brain axis is working; or disrupted in mental health disorders.
An unrelated study reported in mBio used a mouse model to show that a fungus that is a common part of the gut microbiome, called Candida albicans can raise the levels of an inflammatory signal known as PGE2. This molecule is able to cross the blood-brain barrier and it may decrease the desire for alcohol.
When mice had higher PGE2 levels, they became more sensitive to how alcohol disrupted motor coordination, and they avoided alcoholic beverages. But if PGE2’s effects were blocked, they consumed it alcohol again.
A small clinical trial published in Frontiers in Psychiatry has indicated that a fecal microbiota transplant could improve symptoms of depression. There were 347 volunteers who were given fecal microbiota transplants, and 334 volunteers who got a placebo or other control. Those who got the treatment through an enema or endoscopy showed the greatest improvement, though other methods such as oral capsules all resulted in improvements. Patients who also had IBS also tended to show the greatest improvement.
While more research will be needed, a growing body of evidence is indicating that the gut microbiome is not only linked to some mental disorders, but also that manipulating that microbiome could work as a treatment.
Sources: Nature Mental Health, mBio, Frontiers in Psychiatry