Why and Where to Look in the Environment with Regard to the Etiology of Inflammatory Bowel Disease

As inflammatory bowel disease (IBD) continues to emerge with rising prevalence rates in the developed world and rising incidence rates in the developing world, it has become clear that environmental factors play a critical role in disease etiology. While no single environmental factor has been proven to have a definite causative role, there are several leading candidates. Smoking has been shown to adversely impact on the course of Crohn's disease (CD), but is neither necessary nor sufficient to cause CD. Considering that the countries with the highest smoking rates in the world have among the lowest rates of CD, it is more likely that smoking modulates CD once it is present as opposed to being directly causative. Diet likely plays a role, perhaps by modulating the gut microbiome directly or indirectly by impacting on the gut immune homeostasis. Antibiotics have become ubiquitously prescribed in the developed world and their emergence coincided with the emergence of IBD in the middle of the 20th century. Antibiotic use is also increasing in the developing world, and perhaps by modulating the gut microbiome this may be facilitating the emergence of IBD where it was rare 40 years ago. Finally, personal stress has intestinal physiological and immunological effects and is assuming an increasing role in the management of IBD. Copyright (C) 2012 S. Karger AG, Basel