RISK OF INFLAMMATORY BOWEL-DISEASE ATTRIBUTABLE TO SMOKING, ORAL CONTRACEPTION AND BREAST-FEEDING IN ITALY - A NATIONWIDE CASE-CONTROL STUDY

Background Using data from a case-control study carried out in Italy 1 989-1992, we estimated the odds ratios (OK) and the population attribu table risks (AR) for inflammatory bowel diseases (IBD) in relation to smoking, oral contraception and breastfeeding in infancy. Methods The study focused on 819 cases of IBD (594 ulcerative colitis: UC; 225 Cro hn's disease: CD) originating from populations resident in 10 Italian areas, and age-sex matched paired controls. Results Compared with non- smelters, former smokers were at increased risk of UC (OR = 3.0; 95% c onfidence interval [CI] : 2.1-4.3), whereas current smokers were at in creased risk of CD (OR = 1.7; 95% CI : 1.1-2.6). Females who reported use of oral contraceptives for at least one month before onset of symp toms had a higher risk of CD (OR = 3.4; 95% CI : 1.0-11.9), whereas no significant risk was observed for UC. Lack of breastfeeding was assoc iated with an increased risk of UC (OR = 1.5; 95% CI : 1.1- 2.1) and C D (OR = 1.9; 95% CI : 1.1-3.3). Being a 'former smoker' was the factor with the highest attributable risk of UC both in males (AR = 28%; 95% CI : 20-35 %) and in females (AR = 12%; 95% CI : 5-18%). Smoking was the factor with the highest attributable risk for CD in males (AR = 31 %; 95% CI : 11-50%). Lack of breastfeeding accounted for the highest p roportion of CD in females (AR = 11%; 95% CI : 1-22%). Oral contracept ive use accounted for 7% of cases of UC and for 11% of cases of CD. Co nclusions Taken together, the considered factors were responsible for a proportion of IBD ranging from 26% (CD females)to 36% (CD males). It is concluded that other environmental and genetic factors may be invo lved in the aetiology of IBD.