Commonalities in the time trends of Crohn's disease and ulcerative colitis

OBJECTIVE: The analysis of the time trends of inflammatory bowel disease (IBD) is a powerful research tool to assess the contribution of environmental factors to its etiology and to gain insights about possible causative mechanisms. A previous study revealed a characteristic relationship between the time trends of mortality from Crohn's disease and ulcerative colitis. The present study aimed to test whether the most recent temporal patterns still corroborate the hypothesis of two interacting risk factors in the development of IBD. The time trends of IBD from six countries were checked for common features. METHODS: Mortality data from Australia, Canada, England and Wales, the Netherlands, Sweden, and the United States were analyzed. Age- and sex-specific death rates, as well as total death rates, from Crohn's disease and ulcerative colitis were plotted against the period of death. RESULTS: Mortality from ulcerative colitis decreased continuously during the past 40 years. Mortality from Crohn's disease increased between 1950 and the mid-1970's until reaching a similar level as mortality from ulcerative colitis. Since then the death rates of both diseases have followed a parallel time course. A similar behavior was found, if male and female data were analyzed separately. It could be also discerned in the time trends of each age group. The data from all six countries revealed identical temporal patterns. CONCLUSIONS: The similar time trends of IBD from differ ent countries support the hypothesis that identical causative mechanisms are responsible for the mortality and the occurrence of IBD among populations characterized by different political history and health care systems. The rapidity of the temporal changes implicates environmental agents in the etiology of both diseases. The relationships between the temporal changes of Crohn's disease and ulcerative colitis point at the existence of a shared risk factor responsible for the occurrence of both diseases, and at the existence of at least one additional factor, responsible for the expression of Crohn's disease alone. (Am J Gastroenterol 1999;94: 2171-2176. (C) 1999 by Am. Coll. of Gastroenterology).