Did you know that up to 70% of people with anxiety or depression also experience digestive issues? A 2016 study has found that in one-third of individuals, a mood disorder, like anxiety or depression, precedes a gastrointestinal disorder, while in two-thirds of individuals a gastrointestinal disorder precedes a mood disorder. This is a significant finding. An increased understanding of the brain-to-gut and gut-to-brain relationship is opening up new opportunities for the treatment and management of both mental illness and gut disorders.
The Role of our ‘Second Brain’
The gut, or the second brain as it is also referred, is made up of millions of nerve cells lining the gastrointestinal tract from the oesophagus to the rectum. These layers of nerve cells are what scientists refer to as the enteric nervous system (ENS). The ENS can operate independently of the brain and the spinal cord and controls a range of important processes including the release of enzymes to digest food, blood flow control, peristalsis and the elimination of waste. The ENS also communicates back and forth between our brain, and has the ability to trigger emotional changes.
A number of neurotransmitters are also found in the gut. Neurotransmitters are chemicals that relay signals between nerve cells, which allow communication of information between the brain and the body. The gastrointestinal tract uses more than 30 neurotransmitters, most of which are identical to the neurotransmitters used by the brain, including serotonin and dopamine. Serotonin and dopamine play a huge role in mood and cognitive function, with low levels of serotonin and dopamine associated with depression and anxiety.
Here is where it gets really interesting – a whopping 90% of the body’s serotonin is found in the gut, and about 50% of the body’s dopamine. It is unsurprising then that a persons mood can be profoundly affected by the health of their gut, and an abnormal gut microbiome can contribute to mental illnesses like depression and anxiety.
Serotonin Levels Rely on a Healthy Gut Microbiome
Serotonin is produced by certain cells and neurons in the digestive tract. Interestingly, the production of serotonin levels by these cells is greatly affected by the bacterial residents of the gut. Research has shown that mice with an impaired microbiome produce 60% less serotonin than mice with a healthy microbiome, showing clearly that healthy serotonin levels depend on a healthy gut microbiome.
While research into the relationship between our gut microbes and mentall illness is still in its early stages, it is providing an exciting new avenue for the treatment and prevention of these debilitating illnesses.