What Is Irritable Bowel Syndrome?
Irritable bowel syndrome (IBS) is a disorder that interferes with the normal functions of the large intestine (colon). It is characterized by a group of symptoms--crampy abdominal pain, bloating, constipation, and diarrhea.
One in five Americans has IBS, making it one of the most common disorders diagnosed by doctors. It occurs more often in women than in men, and it usually begins around age 20.
IBS causes a great deal of discomfort and distress, but it does not permanently harm the intestines and does not lead to intestinal bleeding or to any serious disease such as cancer. Most people can control their symptoms with diet, stress management, and medications prescribed by their physician. But for some people, IBS can be disabling. They may be unable to work, go to social events, or travel even short distances.
What Causes IBS?
What causes one person to have IBS and not another? No one knows. Symptoms cannot be traced to a single organic cause. Research suggests that people with IBS seem to have a colon that is more sensitive and reactive than usual to a variety of things, including certain foods and stress. Some evidence indicates that the immune system, which fights infection, is also involved. IBS symptoms result from the following:
- The normal motility of the colon may not work properly. It can be spasmodic or can even stop temporarily. Spasms are sudden strong muscle contractions that come and go.
- The lining of the colon (epithelium), which is affected by the immune and nervous systems, regulates the passage of fluids in and out of the colon. In IBS, the epithelium appears to work properly. However, fast movement of the colon's contents can overcome the absorptive capacity of the colon. The result is too much fluid in the stool. In other patients, colonic movement is too slow, too much fluid is absorbed, and constipation develops.
- The colon responds strongly to stimuli (for example, foods or stress) that would not bother most people.
In people with IBS, stress and emotions can strongly affect the colon. It has many nerves that connect it to the brain. Like the heart and the lungs, the colon is partly controlled by the autonomic nervous system, which has been proven to respond to stress. For example, when you are frightened, your heart beats faster, your blood pressure may go up, or you may gasp. The colon responds to stress also. It may contract too much or too little. It may absorb too much water or too little.
Research has shown that very mild or hidden (occult) celiac disease is present in a smaller group of people with symptoms that mimic IBS. People with celiac disease cannot digest gluten, which is present in wheat, rye, barley, and possibly oats. Foods containing gluten are toxic to these people, and their immune system responds by damaging the small intestine. A blood test can determine whether celiac disease is present. (For information about celiac disease, see the Celiac Disease fact sheet from the National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK).)
The following have been associated with a worsening of IBS symptoms:
Researchers have also found that women with IBS may have more symptoms during their menstrual periods, suggesting that reproductive hormones can exacerbate IBS problems.