As nearly every yogurt commercial since the dawn of time has likely reminded you: your gut health is important. Healthy gut bacteria has been shown to perform critical functions in the human body, playing a role in everything from processing nutrients from food, to potentially helping prevent and even treat some diseases, according to Harvard Health. Past studies have associated stress and depression with various digestive issues and diseases, and scientists are interested in further uncovering the relationship between gut health and mental health.
A recent new study found that constipation and depression may both be linked to low levels of serotonin, a neurotransmitter that plays a role in regulating appetite, sleep, and mood, among many other functions. Conducted on mice, the study also showed that an experimental treatment raising serotonin levels in both the mice’s guts and brains may help diminish both conditions.
Past research has supported the theory that some depressed people operate with lower serotonin levels, but the new study, published in Gastroenterology, linked a shortage of serotonin in the gut to constipation — a notable relationship considering that up to a third of people with depression deal with chronic constipation, according to the study.
"The gut is often called the body's 'second brain,'" Dr. Kara Gross Margolis, lead study author, said in a statement. "It contains more neurons than the spinal cord and uses many of the same neurotransmitters as the brain. So it shouldn't be surprising that the two conditions could be caused by the same process."
The mice in the study all had a genetic mutation associated with severe depression in humans that also impaired the mice’s ability to produce serotonin in both the brain and the gut. They displayed depressive symptoms, and the lower serotonin levels in the gut manifested into deteriorated gut lining and stalled movements of substances through the mice’s GI tract — the mouse equivalent of constipation.
The researchers tested an experimental drug on the mice to help raise their gut serotonin levels that successfully treated their constipation. But the connection between the brain and gut’s serotonin levels suggest that the therapy could potentially help treat both conditions, and the study’s next steps are to test the drug in people with depression that’s been treatment-resistant.
Another similar study published recently found that transplanting gut bacteria from rats that were more susceptible to stress to rats that were more stress-resilient made the latter group more likely to adopt depressive-like behavior. "In rats that show depressive-type behavior in a laboratory test, we found that stress changes their gut microbiome—the population of bacteria in the gut," said study author Dr. Seema Bhatnagar in a statement. "When we transplanted bacteria from those stress-vulnerable rats into rats that had not been stressed, the recipient animals showed similar behavior."
The stress-vulnerable rats also reflected higher proportions of certain bacteria, versus their less stressed out peers, and the research adds to the growing body of evidence detailing the interactions between the brain and gut. Both of these studies provide groundwork for future research focusing on treatments for mental health that target areas other than the brain. While more research is needed, the studies also offer a promising glimpse into how stress and mental health disorders like depression may be related to and mediated by other factors like gut health.