Epidemiology of inflammatory bowel disease.

The search for the cause of inflammatory bowel disease through epidemiologic investigation is centered on documenting disease variability and determining the reason for such variability. An examination of the person, place, and time variability of inflammatory bowel disease can provide important clues to disease pathogenesis. Although there is a great deal of variability in the epidemiology of inflammatory bowel disease among populations, there is little difference in these populations between Crohn's disease and ulcerative colitis with regard to person, place, or time variability. With notable exceptions, such as cigarette smoking, the epidemiologic variability of ulcerative colitis and Crohn's disease is remarkably similar. Such similarities are unlikely to be coincidences. The possible implications from this observation are that ulcerative colitis and Crohn's disease are actually different expressions of the same disease, expressions determined by such factors as cigarette smoking, or that two separate diseases share a near complete set of risk factors. Whichever theory is correct, environmental risk factors, which are preventable, are certain to be involved in causative mechanisms.