Smoking and sugar intake are separate but interactive risk factors in Crohn's disease.

Previous studies have consistently found strong positive associations between refined sugar intake and Crohn's disease (CD) and recently between smoking and CD. As refined sugar intake and smoking are themselves associated we have enquired about smoking and added sugar intake (AS) and smoking in CD using a postal questionnaire sent to 104 CD patients and 153 community controls. Smoking and AS were associated with one another. After adjusting for AS, smoking showed a significant association with CD with a relative risk of 1.8. After adjusting for smoking habit, AS was also strongly associated with CD in never and exsmokers and in a dose response pattern, with the relative risks for no AS, less than 50 g/day and greater than 50 g/day being respectively 1.0, 1.8, and 4.6 (chi 2 = 12.1; p less than 0.005). No association between CD and AS was evident in smokers. The AS relationship was supported by a separate association between frequency of confectionery consumption and CD. These findings indicate that while smoking and AS are individually associated with CD combined exposure results in no further increase in risk, suggesting that they may operate through a common mechanism.