Challenges associated with identifying the environmental determinants of the inflammatory bowel diseases

In the last several years there has been an explosion in the discovery of inflammatory bowel disease (IBD) susceptibility genes; however, similar advances in identifying and defining environmental risk factors associated with IBD have lagged behind. Moreover, many studies that have explored the same or similar environmental risk factors of IBD have demonstrated disparate results and come to conflicting conclusions. In order for the field to move forward, it is important to understand and resolve why these differences exist. This significant heterogeneity has blurred the identification of the fundamental environmental determinants of IBD. The purpose of this review article is to explore the factors that have likely contributed to the heterogeneity among observational studies of environmental risk factors in IBD. In doing so, it is hoped that methodological standardization may lead to consistent environmental associations.