In 1982, two Australian scientists identified H. pylori as the main cause of stomach ulcers. They showed that inflammation of the stomach and stomach ulcers result from an infection of the stomach caused by H. pylori bacteria. This discovery was so important that the researchers were awarded the Nobel Prize in Medicine in 2005. The bacteria appear to trigger ulcers in the following way:
- H. pylori's corkscrew shape enables them to penetrate the mucus layer of the stomach or duodenum so that they can attach themselves to the lining. The surfaces of the cells lining the stomach contain a protein, called decay-accelerating factor, which acts as a receptor for the bacteria.
- H. pylori survive in the highly acidic environment by producing urease, an enzyme that generates ammonia to neutralize the acid.
- H. pylori stimulate the increased release of gastrin. Higher gastrin levels promote increased acid secretion. The increased acid damages the intestinal lining, leading to ulcers in certain individuals.
- H. pylori also alter certain immune factors that allow these bacteria to evade detection by the immune system and cause persistent inflammation -- even without invading the mucus membrane.
Even if ulcers do not develop, H. pylori bacteria are considered to be a major cause of active chronic inflammation in the stomach (gastritis) and the upper part of the small intestine (duodenitis).
H. pylori are also strongly linked to stomach cancer and possibly other non-intestinal problems.
Factors that Trigger Ulcers in H. pylori Carriers. Only around 10 - 15% of people who are infected with H. pylori develop peptic ulcer disease. H. pylori infections, particularly in older people, may not always lead to peptic ulcers. Other factors must also be present to actually trigger ulcers, including:
- Genetic Factors. Some people harbor strains of H. pylori with genes that make the bacteria more dangerous, and increase the risk for ulcers.
- Immune Abnormalities. Certain people have an abnormal intestinal immune response, which allow the bacteria to injure the lining of the intestines.
- Lifestyle Factors. Although lifestyle factors such as chronic stress, drinking coffee, and smoking were long believed to be primary causes of ulcers, it is now thought that they only increase susceptibility to ulcers in some H. pylori carriers.
- Shift Work and Other Causes of Interrupted Sleep. People who work the night shift have a significantly higher incidence of ulcers than day workers. Researchers suspect that frequent interruptions of sleep may weaken the immune system's ability to protect against harmful bacteria.
When H. pylori were first identified as the major cause of peptic ulcers, these bacteria were found in 90% of people with duodenal ulcers and in about 80% of people with gastric ulcers. As more people are being tested and treated for the bacteria, however, the rate of H. pylori- associated ulcers has declined. Currently, H. pylori are found in about 50% of people with peptic ulcer disease.
Review Date: 07/18/2011
Reviewed By: Reviewed by: Harvey Simon, MD, Editor-in-Chief, Associate Professor of Medicine, Harvard Medical School; Physician, Massachusetts General Hospital. Also reviewed by David Zieve, MD, MHA, Medical Director, A.D.A.M., Inc.