Serotonin is a neurotransmitter (or chemical messenger) that controls and stabilizes your mood and functions in your brain. What might surprise you is that it’s also crucial to the functions of your digestive system. Your gut produces about 95 percent of the serotonin in your body, and changes in your serotonin level affect your gut as well as your brain.
Irritable bowel syndrome (IBS) is a common condition that primarily affects your large intestine. Causes of IBS are not clearly understood, and symptoms include abdominal cramping and pain, bloating and gas, and diarrhea or constipation. It’s characterized by episodes of flare-ups, which can last days, weeks, or even months.
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The enteric nervous system is a semiautonomous nervous system located in your gut. It’s embedded in the lining of your gastrointestinal system, from your esophagus to your anus, and hundreds of millions of nerve cells direct movement through it. It can perform some tasks on its own, independent of the brain, such as coordinating reflexes and secreting enzymes, one of which is serotonin.
Neural pathways connect your enteric nervous system and your brain, and each affects the other — think of butterflies in your stomach when you're nervous, or having to use the bathroom when you’re anxious, even though you just went. Additionally, flare-ups of IBS in your gut can be caused by stress or anxiety from your brain.
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Serotonin affects many aspects of your gut function, including:
- the motility of your bowels, or how fast food moves through your system
- how much fluid, such as mucus, is secreted in your intestines
- how sensitive your intestines are to sensations like pain and fullness from eating
Some nerve receptors are responsible for sending messages to your brain that signal nausea, bloating, and pain, while others change your sensitivity to or intensity of how distended or full your intestines feel. Levels of each of these receptors vary from person to person. For example, your stomach may interpret what others perceive as a normal feeling of fullness, as pain.
People with IBS who experience constipation often have lower levels of serotonin, the muscles in their rectums are less reactive to serotonin, and they’re more likely to have hard or lumpy stools. Those with IBS and high levels of serotonin can have diarrhea, and their rectums are more reactive, with loose or watery stools.
IBS patients have to deal with a variety of symptoms, not all of which are related to the bowel. Low levels of serotonin may make you more prone to fibromyalgia, a heightened sensitivity to pain in muscles throughout your body. Altered levels of serotonin can also interrupt your sleep patterns and are associated with chronic depression and anxiety disorders.
Selective serotonin reuptake inhibitors (SSRIs) are a group of drugs commonly used to treat depression. These drugs allow more serotonin to be available for your nerve cells to use, but antidepressants and antianxiety medications might not treat IBS. Research continues to look for medications that are specifically designed to treat the serotonin changes seen in IBS without damaging side effects.
Talk to your doctor about current and emerging serotonin-related therapies that could address your specific symptoms. Don't forget that exercise and relaxation techniques like meditation can alter your serotonin levels enough to have a positive impact on your symptoms.
The nervous systems of your brain and your gut are connected by neural pathways, and serotonin plays an important role in both, regulating basic functioning and mood. Serotonin can affect your IBS symptoms, and altering serotonin levels through medication can help treat them.