Scientists have been studying how the human body functions for millennia, yet there are still countless workings that we still do not fully understand. Just in the past decade, health researchers have discovered an interesting connection — one that affects tens of millions of Americans. It turns out the bacteria that naturally occur in everyone’s digestive tract play an important role in our mental health.
The latest evidence on the topic is reported in a systematic review published this month in the journal Clinical Psychology Review. The review includes 26 studies that evaluate the gut microbes in people with symptoms of anxiety and depression, and compare them to the gut microbes of healthy participants.
The review found clear evidence that people experiencing anxiety and depression are more likely to have species of bacteria in their digestive tracts that promote inflammation. In addition, people with anxiety and depression had fewer microbes that produce short-chain fatty acids, which are believed to regulate the central nervous system.
What’s going on here? Scientists still don’t understand the exact mechanisms at work. But there are clues that some bacteria in the digestive tract stimulate the vagus nerve, which controls mood, immune response, digestion, and heart rate. And they believe other bacteria secrete molecules that travel through the bloodstream to reach the brain.
There are indirect links as well, researchers believe. Some evidence suggests that inflammation is a key factor in mental health disorders and that certain combinations of gut microbes promote inflammation. Some research also shows that byproducts secreted by gut microbes trigger the release of the neurotransmitter serotonin (known to help stabilize mood), which escapes the gut and travels throughout the body.
What scientists do know is that connections abound. For example, schizophrenia patients treated with an antibiotic known to kill specific bacteria in the gut had fewer psychotic symptoms after taking the drug. In another study, scientists transferred gut microbes from human participants experiencing depression to healthy rats and then found the rats began experiencing significant symptoms of depression themselves.
What to do with all of this information? There isn’t enough data yet to suggest a specific treatment related to the gut microbiome for mental health. But there is a systematic review indicating that people who eat diets high in fruit, vegetables, fish, and whole grains reduce their risk for depression. Although this review doesn’t examine the microbiome specifically, it is clear that what we eat affects the microorganisms in our digestive systems. For now, the take-home message is that eating a healthy, well-balanced diet not only improves your physical health but likely boosts your mental health as well.
Visit Cornell University’s Bronfenbrenner Center for Translational Research’s website for more information on our work solving human problems.
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