I am a first generation American, as both of my parents immigrated here from Myanmar, a third world country. There had been no occurrence of any Inflammatory Bowel Disease (IBD) in my family, yet I was diagnosed with Ulcerative Colitis at the beginning of my sophomore year of high school. Since IBD is known to be caused by a mix of genetic and environmental factors,1,2 what specifically triggered me to develop Ulcerative Colitis? Was it the food in America, the air I was exposed to, a combination of the two, or neither of them at all? Did the “environment” of the first world in the United States cause me to develop Ulcerative Colitis?
IBD is a chronic autoimmune disease, characterized by persistent inflammation of the digestive tract and classified into two separate categories: Ulcerative Colitis and Crohn’s Disease.3 Currently, there is no known cure for IBD, as its pathogenesis (i.e. the manner in which it develops) is not fully understood.1 Interestingly, the incidence of IBD has increased dramatically over the past century.1 A systematic review by Molodecky et al. showed that the incidence rate of IBD was significantly higher in Western nations. This may be due to better diagnostic techniques or the growth of environmental factors that promote its development. This could also suggest that there may be certain stimuli in first world countries that can trigger pathogenesis in individuals with a genetic predisposition to IBD.
Environmental factors that are believed to affect IBD include smoking, diet, geographic location, social status, stress, and microbes.1 Smoking has had varying effects on the development of IBD depending on the form; smoking is a key risk factor for Crohn’s Disease, while non-smokers and ex-smokers are usually diagnosed with Ulcerative Colitis.4 There have not been many studies investigating the causal relationship between diet and IBD due to the diversity in diet composition.1 However, since IBD affects the digestive system, diet has long been thought to have some impact on the pathogenesis of the disease.1 In first world countries, there is access to a larger variety of food, which may impact the prevalence of IBD. People susceptible to the disease in developing countries may have a smaller chance of being exposed to “trigger” foods. In addition, IBD has been found in higher rates in urban areas versus rural areas.1,4,5 This makes sense, as cities have a multitude of potential disease-inducing environmental factors including pollution, poor sanitation, and microbial exposure. Higher socioeconomic status has also been linked to higher rates of IBD.4 This may be partly due to the sedentary nature of white collar work, which has also been linked to increased rates of IBD.1 Stress used to be viewed as a possible factor in the pathogenesis of IBD, but recent evidence has indicated that it only exacerbates the disease.3 Recent research has focused on the microorganisms in the gut, called gut flora, as they seem to have a vital role in the instigation of IBD.1 In animal models, it has even been observed that pathogenesis of IBD is not possible in a germ-free environment.1 The idea of the importance of microorganisms in human health is also linked to the Hygiene Hypothesis.
The Hygiene Hypothesis states that the lack of infections in western countries is the reason for an increasing amount of autoimmune and allergic diseases.6 The idea behind the theory is that some infectious agents guard against a wide variety of immune-related disorders.6 Animal models and clinical trials have provided some evidence backing the Hygiene Hypothesis, but it is hard to causally attribute the pathogenesis of autoimmune and allergic diseases to a decrease in infections, since first world countries have very different environmental factors than third world countries.6
The increasing incidence of IBD in developed countries is not yet fully understood, but recent research points towards a complex combination of environmental and genetic factors. The rise of autoimmune disease diagnoses may also be attributed to better medical equipment and facilities and the tendency of people in more developed countries to regularly get checked by a doctor. There are many difficulties in researching the pathogenesis of IBD including isolating certain environmental factors and obtaining tissue and data from third world countries. However, there is much promising research and it might not be long until we discover a cure for IBD.
- Danese, S. et al. Autoimm Rev 2004, 3.5, 394-400.
- Podolsky, Daniel K. N Engl J Med 2002, 347.6, 417-29.
- Mayo Clinic. "Inflammatory Bowel Disease (IBD)." http://www.mayoclinic.org/diseases-conditions/inflammatory-bowel-disease/basics/definition/con-20034908 (accessed Sep. 30, 2016).
- CDC. "Epidemiology of the IBD." https://www.cdc.gov/ibd/ibd-epidemiology.htm (accessed Oct.17, 2016).
- Molodecky, N. et al. Gastroenterol 2012, 142.1, n. pag.
- Okada, H. et. al. Clin Exp Immuno 2010, 160, 1–9.