Risk factors for ulcerative colitis: A population-based, case–control study in Spain

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Background: Environmental factors seem to be very important in the aetiology of Ulcerative Colitis (UC), with smoking, contraceptive use, and hygiene being the factors most commonly linked to disease.

Aim: To analyse the association between different risk factors and development of UC in our community.

Patients and methods: This is a case–control, population-based study. The UC population consists of an inception-case population of all cases diagnosed, using Lennard–Jones criteria, in our community from 1st February 1992 to 31st January 1995 that were prospectively included. Controls were selected from healthy population and matched with patients for age, sex and rural/urban habitat. We used the SPSS/PC+ software, EpiInfo and Statistix for statistical analysis, giving the rates as point estimates and 95% confidence intervals (95%CI) or as mean ± standard deviation in quantitative variables. For multivariate analysis we used conditional logistic regression.

Results: 205 patients were diagnosed of UC. 38 patients (18.5%) with UC were smokers, compared with 84 (40.8%) controls (p < 0.001). Smoking behaved as a protector factor for UC (OR = 0.55 (CI 95% 0.33–0.92) and ex-smoker acted as a risk factor (OR = 1.94 (CI 95% 1.14–3.34). After the multivariate analysis, both associations were maintained. We did not detect statistical differences in the analysis of previous appendectomy, childhood hygiene or oral contraceptive use. Five of the 12 cases with family aggregation had first-degree relatives and 7 of them second-degree relatives. None of the controls had previous IBD history (p = 0.0002).

Conclusion: Ex-smoking and previous family history of inflammatory bowel disease appeared as risk factors for developing ulcerative colitis while current smoking behaved as a protective factor in this population.

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