Background: A few cross-sectional studies reported an increased risk of inflammatory bowel disease (IBD) among asthmatics. We conducted a population-based, case-control study that applied predetermined criteria for asthma and IBD to determine whether asthma, as a T-helper 2 (Th2) condition, reduces the risk of IBD, a Th1 condition.
Methods: This was a population-based, case-control study using criteria-based ascertainment for IBD and asthma. Subjects were all Rochester, Minnesota, residents who had developed IBD between 1964 and 1983 and their age- and gender-matched controls, using 1:1 matching. Controls were randomly selected from the community using the Rochester Epidemiology Project database and confirmed not to have IBD. All cases and controls were merged with the database comprising all Rochester residents with or without asthma between 1964 and 1983.
Results: Of the 231 IBD cases, 55% had ulcerative colitis and the remainder had Crohn's disease. Of these, 50.4% were male and 98.1% were Caucasians. The mean age at the time of IBD diagnosis was 33.8 years. Four cases (1.7%) had asthma prior to the index date of IBD, whereas two controls (0.9%) had asthma (unadjusted odds ratio [OR]: 3.0, 95% confidence interval [CI]: 0.31-28.84, P = 0.34). Similarly, 16 IBD cases (6.9%) had asthma ever while 12 controls (5.2%) had asthma ever (unadjusted OR: 1.4, 95% CI: 0.62-3.38, P = 0.40).
Conclusions: Asthma as a Th2 condition does not reduce the risk of IBD as a Th1 condition. Because of the limitations of our study and others, the association between asthma and IBD needs to be further studied.