Possible Environmental Causes Of Inflammatory Bowel Disease (IBD)

There are differences in the prevalence of Crohn's disease and ulcerative colitis between countries, as well as between ethnic groups within a given country. These differences have led scientists to suggest that, in addition to infections, other environmental factors, such as toxins, diet, smoking, medication use, and even geography, may have a significant influence on the development of IBD.

 

 

We know that environmental factors influence IBD from studies of twins. When one identical twin has Crohn's disease or ulcerative colitis, the other twin, who is genetically identical, will not necessarily develop IBD. To produce the disease, some environmental influence or exposure must interact with the genetic background that makes a person susceptible to developing IBD. Presumably, one twin has been exposed to disease-causing environmental factors, while the other has not been exposed to those factors or has not been exposed for long enough or exposed at the right time in the course of growth and development.

 

 

There have been a number of ways in which researchers have tried to determine what some of these environmental factors might be. Often, they will take a group of IBD patients and find out about various possible risk factors that they might have been exposed to and compare them to a group of similar individuals who do not have IBD. Researchers will also examine where people with IBD were born and where they grew up while looking for clues to possible environmental exposures.

 

Through these studies, it has been discovered that the incidence of IBD is highest in developed North American and Northern European countries and lower in less developed or more southerly countries. This has raised the theory that something we are exposed to in developed countries contributes to the development of IBD. An interesting observation is the change in the pattern of IBD in other areas of the world. In Japan, for example, Crohn's disease was almost unheard of in 1950, but the incidence of the disease has risen steadily since then. This increase has been explained by some experts as the result of a change in the Japanese diet. During the time that Crohn's disease has increased in Japan, the diet has become increasingly Westernized, with less traditional rice and fish and more red meat being eaten. However, the change in diet and the increase in incidence do not prove cause and effect since many other aspects of life in Japan changed between 1950 and the present time.

 

 

Dietary factors are obvious potential risk factors given that Crohn's disease and ulcerative colitis are intestinal disorders. Food comes into direct contact with the intestinal lining. Although no specific food or food category has been consistently found to be a potential triggering factor in IBD, some studies have found that diets that are high in red meat or refined sugars may increase the risk of developing IBD.

 

Altering dietary intake may result in improvement in intestinal inflammation and symptoms of disease. This is not to say that dietary factors cause IBD, but once IBD is established, modification of the diet may, in some instances, improve the disease activity and symptoms.

 

There may be some factor in the diet that worsens or propagates the inflammatory reaction in the intestines of IBD patients. It is not clear what this factor or factors might be. Attempts at carrying out exclusion or elimination diets, in which specific foods are removed from and then added back into the diet one at a time, have not identified a specific food trigger in the majority of patients.

 

 

The relationship between cigarette smoking and IBD has long been known. Patients with ulcerative colitis are more likely to be non-smokers or former smokers, and patients with Crohn's disease are more likely to be smokers. How cigarette smoking interacts with other factors to either increase or decrease the risk of disease is entirely unknown.

 

 

Some medications are known to cause irritation and even damage to the lining of the intestinal tract. Aspirin and non-steroidal anti-inflammatory drugs (for example, ibuprofen, naproxen, diclofenac, and sulindac) are well known to cause ulcers in the stomach and duodenum. These drugs can also have damaging effects on the lining of the intestinal tract in the last part of the small intestine (ileum) and the large intestine, the areas most commonly affected in IBD.