Environmental Risk Factors
There also appears to be an environmental component to the disease that creates an abnormal immune response. Typically, your immune system identifies harmful agents like unhealthy bacteria and viruses and destroys them. But, in Crohn’s disease, the immune system appears to attack beneficial bacteria causing an excess of white blood cells to accumulate in the lining of the intestines. This autoimmune response causes chronic inflammation of the intestines. Researchers believe that the autoimmune response might be triggered by environmental factors that are still under study.
Here are some of the environmental risk factors that are believed to either protect against or contribute to the development of inflammatory bowel disease (IBD):
- Breastfeeding has been shown to reduce the risk of developing IBD in both Western countries and in Asia when infants were breastfed for more than 12 months. In Asia, infants who were breastfed were seven to 10 times less likely to develop either Crohn’s disease or ulcerative colitis.
- Smoking is known as a risk factor for developing Crohn’s disease in the Western world, this association may not be consistent throughout the world. For example, one study demonstrated that smoking was not a risk factor for Crohn’s disease for individuals living in countries in Asia, despite high rates of smoking, but quadrupled the risk of developing Crohn’s disease in Australia. In contrast, quitting smoking increased the risk of developing ulcerative colitis in both the Western world and in Asia.
- Physical activity physical activity may help prevent the development of Crohn’s disease. A study conducted in Asian countries showed that those with sedentary lifestyles were twice as likely to develop Crohn’s disease as more active individuals.
- Hygiene and antibiotics. The hygiene hypothesis, postulates that improved sanitation increases the risk of developing IBD. This view states that modern, sanitized conditions expose children to fewer microbes and therefore their immune systems may not fully develop. Consequently, these children become more susceptible to IBD later in life. The hygiene hypothesis is a widely accepted theory in the Western world. It is also substantiated by several studies from North America that have shown that exposure to antibiotics in childhood increase the risk of developing IBD later in life. In contrast, studies from Asia show that children exposed to antibiotics and improved sanitary conditions (flush toilets) had a protective factor against ulcerative colitis. So, these mixed results suggest that different environmental factors may influence the development of IBD in Asia.
Though several environmental risk factors are undeniably involved in the development and spread of IBD globally, it is unclear which risk factors play the greatest part in the ongoing development of IBD.
What seems more certain is that IBD is emerging as a global disease and appears to be on the rise. Future studies are needed to better understand the common and the contrasting risk factors between Western and Asian countries.
Geography and Genetics
Genetically, Crohn’s disease tends to run in families. Those with a first-degree relative with the disease are at higher risk for getting the disease.
Traditionally, IBD has been characterized as a disease of Caucasians of European descent living in industrialized societies. Recent studies have shown that IBD is not primarily an issue of ancestry or ethnicity. The rate of IBD differs between regions where the genetic background is similar. IBD afflicts individuals of all ethnic groups whose families have lived in the western world for many generations.
During the 20th century, the diagnosed rate of IBD cases has steadily increased in western world regions, such as North America, Europe, Australia and New Zealand and currently represents 0.5% of the general population of those areas. In the United States alone, over 1 million individuals are estimated to suffer from IBD. In Europe, it is estimated that 2.5 – 3 million people live with IBD. But rates vary by location. Europe has a higher rate of ulcerative colitis while Australia has a higher occurrence of Crohn’s disease. IBD is equally distributed in North America. At present, it is clear that the majority of patients with IBD live in the Western world.
There is also some evidence that pediatric-onset of IBD is on the rise in the Western world. For example, rates of diagnosed IBD are significantly increasing in children under 10 years of age. When IBD begins at such an early age, the disease is more pervasive and serious when compared with adult onset. The recent trend in pediatric-onset IBD shows that affected individuals come from a wide range of different cultural backgrounds. For example, if a child from a low prevalence country, such as India, moves to a high-prevalence country, such as Canada, then their chance of developing IBD increases to that of Canada. Therefore, genetic risk does not explain the trend analysis over the past century.
IBD is Increasing
While rates have plateaued in some of these western areas, developing countries that are relatively new to modern industry in Asia, South America and the Middle East are seeing a significant increase in diagnosed IBD cases. Until the middle of the 20th century, IBD was relatively rare in developing countries but since that time rates of IBD have steadily grown. Though the overall number of diagnosed cases of IBD in newly industrialized countries is significantly lower when compared to developed countries, IBD is increasing at a much higher rate than in Western world countries. And projections suggest a significant global increase of IBD in the next decade.
It is accurate to call IBD a modern disease because it has emerged alongside 20th century western culture advances in transportation, agriculture, manufacturing, urbanization and dietary habits. During this time period there have been dramatic shifts in how modern society functions. We’ve transitioned from a mostly rural setting to urban living; from a farming society to an industrial one and from a survival mentality to a consumeristic mindset. Along with these changes we’ve adopted lifestyle behaviors such as smoking, low-fiber diets, less physical activity and exposure to environmental toxins. Combine these changes with advancements in our economic and social environments, along with better healthcare access and delivery, and IBD emerges as a disease of affluence.
Several studies have established that IBD has now taken hold in newly industrialized countries and parallels the growth patterns of the western culture in the 20th century. Epidemiologic studies have consistently shown a rapid rise in the rates of ulcerative colitis and Crohn’s disease in countries that transition from developing to industrialized economies. As developing countries become westernized, IBD should become more prevalent.
Note: for a more comprehensive overview of all the environmental risk factors studied in IBD, please see this open access article published in the Canadian Journal of Gastroenterology and Hepatology.