Previous studies have consistently found strong positive associations between smoking and Crohn's disease. The association between oral contraceptive use and Crohn's disease remains, however, controversial. In order to analyze whether smoking and oral contraceptive use are independent risk factors, a case-control study was performed. In 90 women with Crohn's disease and 90 community controls information was assessed about their smoking habits and their use of oral contraceptives. Smoking and oral contraceptive use were associated with one another. After adjusting for oral contraceptive use, the relative risk for smokers compared with nonsmokers was 3.0 (1.3-6.8). After controlling for smoking, the relative risk estimates for oral contraceptive use were for no use, 1-3 years, and > 3 years of use 1.0, 2.5 (1.0-6.6), and 4.3 (1.3-14.4), respectively. When oral contraceptive use was stratified by smoking habits, the data show that oral contraceptives only increased the risk for Crohn's disease in nonsmokers. From the lack of increase in risk for combined exposure, it is concluded that both factors might act through a common mechanism.
PIP: In West Germany, gastroenterologists enrolled 90 woman with Crohn's disease at the outpatient clinic of the University Hospital Essen for follow-up between January 1986 and January 1988 in a case-control study designed to examine the relationship between smoking and oral contraceptive (OC) use and Crohn's disease. The 90 age-matched controls lived in Essen. When the researchers adjusted for OC use, the relative risk (RR) of Crohn's disease for smokers compared with nonsmokers stood at 3. The risk did not increase in former smokers, however (RR = 0.69). When they controlled for smoking, the RR increased with duration of OC use (2.5 for 1-3 years and 4.3 for 3 years). When the researchers stratified OC use by smoking habits, the risk for Crohn's disease increased only for nonsmokers (RR = 3.1). Smoking and OC use were associated with each other. Smoking and OC use were especially strong risk factors for Crohn's disease afflicting only the small intestine (RR = 6.2 and 4.7, respectively). Since combined exposure to both smoking and OC use did not further increase the risk for Crohn's disease, it is concluded that they might operate through a common mechanism.