What causes Barrett's esophagus?
Gastroesophageal reflux disease (GERD)
GERD causes Barrett's esophagus. The esophagus is a muscular tube that is located in the chest and serves to transfer food from the mouth to the stomach. The lower esophageal sphincter (LES) is a valve that is located at the junction of the stomach with the esophagus . Its function is to prevent acid and other contents of the stomach from coming back into the esophagus. GERD is a condition in which excessive acid-containing fluid refluxes (flows) back into the esophagus, in part because the lower esophageal sphincter is weak. The weakness of the LES may be related, in part, to the fact that virtually all GERD patients have hiatal hernia. In hiatal hernia, the upper few centimeters of the stomach slides back and forth between the abdomen and the chest through the diaphragm. This sliding may interfere with how the sphincter works as a barrier to reflux from the stomach to the esophagus.
Previously, the term hernia was used instead of GERD in explaining to patients the basis of their symptoms (usually heartburn) because virtually all GERD patients have hiatal hernias. GERD, however, is the more accurate term. Hiatal hernias are extremely common in the population and yet only a small number of people with hiatal hernia develop GERD. In other words, the presence of a hiatal hernia does not mean that the person will develop GERD. On the flip side, however, if a person has GERD, hiatal hernia is almost always present.
Thus, Barrett's esophagus is caused by chronic (of many years duration) and usually severe acid reflux. In some patients with GERD, the esophagus reacts to the repeated injury from the acidic fluid by changing the type of cells lining it from squamous (normal cells) to columnar (intestinal-type cells). This transformation, called metaplasia, is believed to be a protective response because the specialized columnar epithelium (epithelium means lining) in Barrett's esophagus is more resistant to injury from acid than the squamous epithelium.
Other contributors to Barrett's esophagus
The fluid in the stomach contains acid that is produced by the stomach. In addition, however, the fluid may contain bile acids (from bile produced by the liver) and enzymes (produced by the pancreas) that have refluxed back from the duodenum into the stomach. (The duodenum is the first part of the small intestine just beyond the stomach.) The acid that refluxes from the stomach to the esophagus is injurious to the esophagus. There is some evidence, however, that the bile and pancreatic enzymes combined with the acid may be more injurious than acid alone.
Who develops Barrett's esophagus?
Approximately 10% to 15% of individuals with chronic symptoms of GERD develop Barrett's esophagus, and it is estimated that Barrett's esophagus may affect as many as one in 100 to one in 500 individuals in the general Caucasian population, especially among males. Not everyone with GERD has symptoms of GERD, however. Therefore, some people with Barrett's are unaware that they have Barrett's because they have GERD without any symptoms at all or have very mild and infrequent symptoms.
It is unclear why Barrett's esophagus is so overwhelmingly more common in white males than in any other group. For example, although women and African-Americans do not seem to be protected from developing GERD, they are largely protected (especially African-Americans) from developing Barrett's esophagus and Barrett's cancer (adenocarcinoma). There is evidence that in the western hemisphere, esophageal cancer and cancer of the gastroesophageal junction (called cardia cancer) are increasing in frequency, perhaps more so than any other gastrointestinal tract cancer. (You should know, however, that colon cancer is still very much more common than esophageal cancer.)
Barrett's esophagus may run in some families and be genetically determined. Studies are underway to determine if any genes or markers can be found in these families that would predict the development of Barrett's esophagus in the general population. In these families with Barrett's as well as with Barrett's in the general population, GERD is the common denominator. However, the question is why the Barrett's occurs more commonly in these families than in others with comparably severe GERD, but with no family association.