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In irritable bowel syndrome (IBS), the colon becomes extremely sensitive and reactive. The cause of IBS is unknown. Most researchers believe that IBS is most likely caused by a combination of genetic, environmental, and psychosocial factors. While researchers have established that certain factors influence a person’s risk for developing IBS, it is not yet known why some people get IBS and some people don’t.
It is important to note that while science is good at finding correlations, or apparent relationships, between factors and disease, correlation does not prove that the factor causes the disease. Many risk factors for irritable bowel syndrome have been identified and are being studied, but none have been pinpointed as the cause of IBS.
Age seems to be a factor in the development of irritable bowel syndrome. Most people who develop IBS are under the age of 50.
Scientists have studied 60 different genes suspected to contribute to the development of IBS. Some studies have indicated that there is likely a genetic component in the risk for developing IBS, while others showed no evidence that IBS is an inherited disorder. One study showed that having a close relative (parent or sibling) with IBS makes you three times more likely to develop the condition yourself. Most researchers agree that IBS runs in families.
Gender seems to influence who gets IBS. Women are about twice as likely to develop IBS as men. Some women with IBS report that their bowel symptoms worsen during menstrual periods.
In some people, irritable bowel syndrome develops after a severe case of gastroenteritis, also known as stomach flu. The risk is higher the longer the infection lasts. Scientists think the infectious agent may cause changes in the cells of the gastrointestinal (GI) tract. It may take eight to 10 years for IBS to develop after an infection. Infectious agents identified as possible causes of IBS include noroviruses, Giardia, E. coli O157:H7, Campylobacter jejuni, Salmonella, and Shigella. Because bacterial infections may cause IBS, bacterial pollution of the local water supply is a risk factor for IBS.
In a related theory, some researchers believe that imbalance of the healthy intestinal bacterial colonies – known as the gut flora or microbiota – may cause IBS to develop. Apart from infectious agents, antibiotics, diet, and an overgrowth of bacteria in the small intestine are known to change the balance of the gut flora.
Studies suggest that environmental air pollution may contribute to imbalances of the bacterial colonies in the gut, which could promote the development of IBS. There is some evidence that IBS symptoms become more severe and result in more emergency room visits when air pollution reaches high levels.
Many doctors consider functional GI disorders like IBS to be caused by communication problems between the gut and the brain. By some estimates, more than 50 percent of people who seek treatment for IBS have a psychiatric disorder such as depression or anxiety. Many of those with IBS report that IBS symptoms worsen with emotional stress. According to some studies, as many as 50 percent of people with IBS report having experienced childhood abuse. In general, those with IBS report more experiences of trauma and abuse throughout life than those without IBS. Some researchers theorize that traumatic experiences cause changes to the brain and nervous system that impact the gut, causing it to be sensitized and reactive. In some people, IBS symptoms improve after they receive treatment for depression, anxiety, and stress.
Can IBS be prevented?
Since we do not yet know what causes some people to develop irritable bowel syndrome, there is no certain way to avoid getting IBS.