Background: The etiology of Crohn’s disease and multiple sclerosis is unknown. Genetic susceptibility and environmental factors are believed to play a role in both diseases.
Objectives: To compare the long-term time trends of the two diseases and thus gain insight about their etiology.
Methods: We analyzed mortality data of Crohn’s disease and multiple sclerosis from Canada, England, Italy, the Netherlands, Switzerland, and the United States during the past 60 years. Age–period–cohort (APC) analyses based on logit models served to disentangle the separate influences of age, period, and cohort effects on the overall time trends.
Results: The long-term time trends of Crohn’s disease and multiple sclerosis have been shaped by strikingly similar birth-cohort patterns. In both diseases alike, mortality increased in all generations born prior to 1910. It peaked among generations born between 1910 and 1930 and then declined in all subsequent generations. Similar birth-cohort patterns of Crohn’s disease and multiple sclerosis were found in each country analyzed separately.
Conclusion: The birth-cohort patterns indicate that the development of Crohn’s disease and multiple sclerosis is influenced by exposure to environmental risk factors during an early period of life. These environmental risk factors may be similar or even identical in Crohn’s disease and multiple sclerosis.