Causes of Irritable Bowel Syndrome

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The actual causes of Irritable bowel Syndrome or IBS is as yet unclear. Some researchers speculate that the disease has roots in the central nervous system while another theory speculates that its associations are with the body’s immune system.

IBS and the central nervous system

The intestinal wall is composed a layers of mucus membranes and muscles. These are richly supplied by blood vessels and nerve endings. These networks are directly connected to the brain.

If there is too much stress and anxiety or lack of sleep there is release of certain chemicals and neurotransmitters leading to squeezing of the intestinal muscles leading to pain, cramps and other symptoms.

Too much of stagnation or contraction of one area leads to non-movement of the food within the intestine. This leads to drying of the food bolus and constipation.

Too much intestinal movement caused by nervous triggers leads to passage of loose watery stools and mucus leading to diarrhoea. (1)

IBS and the body’s immune system

There is another hypothesis that sufferers of IBS are usually more sensitive to certain food types. They have a damaged immune system that normally aids in fighting infections.

The intestinal linings are covered by a layer of cells called the epithelium. This is affected by both the immune and nervous systems.

The immune system controls the flow of fluids into and out of the intestines. In patients of IBS, due to too fast or slow movement of the intestine the fluid flow is misbalanced.

Some researchers suggest that IBS has a basis in a bacterial infection of the gut. This is often seen as a “post-infection” or Post-gastroenteritis” IBS.

Celiac disease is another gastrointestinal disease that makes the patients intolerant to certain foods that contain gluten. On gluten intake their intestines show severe inflammation and their immune systems go into an overdrive.

Sometimes IBS may mimic mild Celiac disease. A confirmatory blood test is required to exclude Celiac disease. (2)

IBS and Serotonin

Serotonin, a central chemical messenger in the brain and nerves, is also implicated in IBS.

Serotonin is useful for normal gastrointestinal workings. Most of the serotonin lies in the gastrointestinal tract and only small amounts are seen in the brain. These act via certain receptors.

Once the messenger binds to the receptor the activity is performed or information is relayed.

In individuals with IBS these receptors are lower in number. Thus the levels of free and unbound Serotonin rises and this may lead to some of the symptoms of IBS like increase sensitivity to pain, disturbed bowel motions etc. (2)

Risk factors that may trigger IBS

There are some risk factors or triggers that aggravate IBS symptoms. These include (3)–

  1. Food. Some people develop aggravated symptoms of pain, cramps and deranged bowel movements after a meal. In some, certain foods like milk and milk products, wheat, barley, rye, alcohol, coffee, tea, colas, sugar and candies and some fruits and vegetables may lead to aggravation of symptoms. The underlying cause may be food allergies but is not clear.
  2. Stress, anxiety, loss of sleep may aggravate IBS symptoms. Sometimes stress and anxiety may be cause for the condition as well.
  3. Hormonal changes – In women symptoms are usually worse during menstrual periods. This raises speculation that changes in blood levels of female sex hormones may be linked to IBS.


Further Reading

Last Updated: Jun 9, 2023

Dr. Ananya Mandal

Written by

Dr. Ananya Mandal

Dr. Ananya Mandal is a doctor by profession, lecturer by vocation and a medical writer by passion. She specialized in Clinical Pharmacology after her bachelor's (MBBS). For her, health communication is not just writing complicated reviews for professionals but making medical knowledge understandable and available to the general public as well.


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