by Emma Bouck
It can be very difficult to be in a good mood when you have a stomachache. Having negative emotions can even create stomachaches, like the nervousness you might have before a difficult test. This link between our brain and our stomach might be more complicated than you realize.
Serotonin is a molecule that helps us be happy by regulating our emotions and keeping us calm. People with mental health conditions like depression or anxiety are thought to have lower levels of serotonin. Common medications for those struggling with mental health are called selective serotonin reuptake inhibitors and function by increasing serotonin in the body. But where does serotonin originally come from?
Since serotonin is active in the brain, it’s reasonable to think that serotonin is produced there. Surprisingly, 95% of your serotonin is produced in the small intestine by the bacteria that live there, not your own human cells.
In our bodies, we have slightly more bacterial cells than our own human cells. Most of these bacteria live in our digestive tract and are called the gut microbiome. These bacteria respond to the nutrients in our food and can break down components like fiber, which are difficult for our own cells to process.
Together, our digestive tract cells and gut microbiome digest our food. In response to certain foods, the gut bacteria may change their production of molecules like serotonin. In this way, a balanced diet can have a big effect on your mental health. For example, the amino acid tryptophan, rumored to cause post-turkey naps on Thanksgiving, is important for serotonin production.
There are about 500 million neurons that are intertwined with your digestive tract and communicate back and forth with your brain. This communication influences your mood, but your brain also instructs your gut on how to digest food based on signals from serotonin and other similar molecules. If you are experiencing a bad mental health day, your digestion may also be impaired, preventing your brain from getting the fuel it needs, causing further disruption to your mental health.
In addition to direct communication between your intestines and nervous system, serotonin also circulates in the bloodstream. Platelets are cells that help blood clot and control inflammation when you get injured, and they also carry around a majority of the circulating serotonin. Fascinatingly, the amount of serotonin in your platelets can impact their function: reduced levels of serotonin can render platelets less reactive at sites of inflammation, which can potentially impair healing.
When platelets encounter inflamed tissue, they release the serotonin being carried inside. This serotonin then helps to regulate all of the cell types that participate in inflammation to make sure their roles are carried out properly.
Autoimmune disorders occur when the immune system mistakenly starts attacking its own body. Platelets and other inflammatory cells are responsible for creating off-target or inappropriate inflammation that makes people with autoimmune disorders ill. Considering the role of serotonin and platelets in mood stability, scientists hypothesize that mental health and some autoimmune conditions may be linked. Scientists believe selective serotonin reuptake inhibitors may be an effective strategy to suppress autoinflammation.
Serotonin may be at the center of health issues related to mood, digestion, and autoimmunity. If scientists can learn more about these relationships, we will be closer to helping people feel better in numerous ways.
