Anxiety and depression could be caused by the gut bacteria living inside the digestive tract according to scientists from the Farncombe Family Digestive Health Research Institute at McMaster University.
The first of its kind study, published in Nature Communication, explored how gut bacteria could be linked to negative behaviors as a result of stress occurring early on in life.
Researchers exposed mice to early life stress by way of maternal separation. From age 3-days old to age 21-days old, the infant mice were separated from their mothers for three hours daily and then returned. The mice with complex gut bacteria that were separated from their mothers displayed more anxious and depressed behavioral characteristics, and also tested with abnormally high levels of the hormone corticosterone, a hormone that rises in the body in an attempt to calm anxieties.
The mice also showed increased disturbed gut function as shown by a disruption in acetylcholine, a neurotransmitter that has recently been thought to be the primary cause of depression.
According to Premysel Bercik, primary author of the study, neonatal stress increases stress and disturbed gut function. This changes the gut bacteria, which then interrupts the proper functioning of the brain.
The researchers repeated the experiment in a germ-free environment. They found that although the mice still contained altered levels of stress hormone and disrupted gut bacteria, they did not show any signs of anxiety or depression.
Gut bacteria was also transferred from the stressed mice into non-stressed, germ-free mice. No signs of anxiety or depression were observed.
Bercik says that it is not only the gut bacteria that is responsible for increasing anxiety and depression, but the distorted communication between the mice and their gut bacteria.
“We are starting to explain the complex mechanisms of interaction and dynamics between the gut microbiota and its host. Our data show that relatively minor changes in microbiota profiles or its metabolic activity induced by neonatal stress can have profound effects on host behavior in adulthood.”
This new research may be used by the field of psychiatric disorders, and Bercik affirms that the investigation is a step into understanding how gut bacteria can help shape behavior.
“It would be important to determine whether this also applies to humans. For instance, whether we can detect abnormal microbiota profiles or different microbial metabolic activity in patients with primary psychiatric disorders, like anxiety and depression.”
According to the Anxiety and Depression Association of America, anxiety disorders are the most common mental illness in the United States, affecting 40 million adults age 18 years and older. Anxiety and depression may occur together. Approximately 3-5 percent of individuals suffer from depression at any time, and the lifetime risk is estimated to about 17 percent.
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