Objective: To determine whether the previously reported decreased risk of ulcerative colitis in current smokers and increased risk in former smokers are explained by age, sex, race, ethnicity, or socioeconomic status.
Design: We conducted a case-control study at a university hospital gastroenterology clinic.
Material and methods: One hundred patients with ulcerative colitis and 100 age- and sex-matched community control subjects were randomly selected for a telephone interview to collect information on smoking habits, race, religion, income, education, and occupation. Smoking habits at the onset of symptoms were analyzed with use of conditional logistic regression for matched data to obtain adjusted odds ratios and 95% confidence intervals for current or former smokers.
Results: In comparison with those who had never smoked, current smokers were less likely to have ulcerative colitis: odds ratio = 0.13; 95% confidence interval = 0.05 to 0.38. Former smokers had no increased risk for ulcerative colitis: odds ratio = 1.24; 95% confidence interval = 0.52 to 2.95. No dose-response effect was noted on the basis of pack-years of cigarette smoking, and among former smokers, the interval since quitting smoking was not significantly associated with the relative risk of ulcerative colitis. No confounding effect was detected from race, religion, income, education, or occupation.
Conclusion: An association seems to exist between ulcerative colitis and nonsmoking; perhaps patients with ulcerative colitis who smoke are less likely to experience symptoms than are nonsmokers because of the effects of nicotine.