WASHINGTON, November 19, 2013—Several new studies are finding a link between the gut bacteria, brain chemistry and mental health. Even though in its beginning stages, this exciting new field of research holds a lot of promise.
Bacteria cells in the human body outnumber huuman cells ten to one, each person having an average of 1,000 trillion bacteria living in a delicate balance inside their body. The average human carries around about five pounds of bacteria, mostly in their gut. Bacteria in the gut perform several functions including digestion, protecting against infection, and providing nutrition to certain cells.
Babies begin with a sterile digestive tract, collecting their first bacteria while traveling through the birth canal and subsequently through breast milk. Gut bacteria continue to develop as the baby has contact with the outside world and other people.
Often called the “second brain” in research circles, the gut also contains more neurons than the spinal chord or peripheral nervous system, estimated at over 100 million. The vagus nerve provides a direct link between the gut and the brain. Science has already established a link between the vagus nerve and mood. Stimulation of the vagus nerve by an electrode that is implanted is a current treatment for depression.
It now appears that bacteria and bacteria levels in the gut, known as microbiota, may also have an influence over brain function and mood.
There is growing anecdotal evidence that a change in gut bacteria can have a significant impact on conditions like obsessive–compulsive disorder (OCD), attention deficit hyperactivity disorder (ADHD), and Pediatric Autoimmune Neuropsychiatric Disorders Associated with Streptococcal infections (PANDAS), as well as depression and anxiety.
For example, Dr. James Greenblatt, a psychiatrist and founder of Comprehensive Psychiatric Resources Inc. in Waltham, Massachusetts, told ABC News that he has successfully treated young patients diagnosed with severe OCD, ADHD and several digestive problems with probiotics and antibiotics targeted toward changing gut bacteria composition. Hundreds of doctors are doing the same.
The link between gut bacteria and brain function goes beyond the anecdotal, however.
A 2011 study published in the journal “Gastroenterology” found that the presence and amount of certain gut bacteria in mice had an effect on their behavior. The scientists first used antibiotics to disrupt healthy bacteria in adult mice. As a result the mice became less anxious and more daring.
To confirm their findings, researchers in a 2013 follow-up study transplanted fecal microbiota from an anxious strain of mice into the guts of young mice belonging to a calm strain and vice versa. The mice from the anxious strain became more confident and calm, while the mice from the calm strain became very nervous after the transplant, suggesting that certain behaviors are determined more by the bacteria in the gut than by the brain or genetics.
While humans have a more complicated microbiota and nervous systems, there also seems to be a link between gut bacteria and brain function in humans.
A 2010 study published in “Nutritional Neuroscience” showed elevated levels of the metabolite HPHPA, in urine samples of children with autism and individuals with schizophrenia. HPHPA is a byproduct of clostridia, a type of bacteria found in the intestines of several animals, including humans.
A UCLA study published in 2013 looked at 36 women to determine whether eating fermented yogurt—high in probiotics—had any effect on brain function. The women, without previous psychiatric symptoms, were divided into three groups where 12 ate fermented yogurt with probiotics, 11 ate a milk product that did not contain probiotics and 13 were used as controls with no intervention in their diet.
After four weeks, researchers studied functional MRIs of the women’s brains. Scientists found that there were function changes in areas of the brain associated with sensation and emotion in the women who ate the fermented milk product with probiotics.
The UCLA study, while small, is among the first human studies to suggest a link between gut bacteria and brain function. There are several larger and more comprehensive human studies underway, however. Moreover, the National Institutes of Mental Health recently called for grant submissions to investigate this new area of research.
While still in its initial stages, however, using probiotics to treat mood, anxiety and possibly a host of other diagnoses should not be considered a magic cure.
“As exciting as these investigations may be, research on how gut bacteria affect psychological well-being in humans is still in its infancy,” writes Dr. Siri Carpenter in an article for the American Psychological Association. “For one, the studies have been almost entirely limited to rodents. Second, researchers have only begun to probe how such effects occur. Finally, correcting microbial imbalances to treat disease requires first defining what constitutes a healthy gut microbiome—something that scientists are still trying to understand.”
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