External Risk Factors For Crohn’s Disease


People get inflammatory bowel disease from a combination of genes and environmental triggers. Having the right (i.e. wrong) genes makes a person more likely to develop IBD in the presence of the right (wrong) external factors. In a previous post, we looked at both causes of IBD; this post takes a closer look at the external factors that cause Crohn’s Disease.

In 2013, the journal Gastroenterology and Hepatology published a two-part review* of the known “environmental” factors that can be associated with Crohn’s Disease. Why only CD? The authors don’t say, but some of the studies mention Ulcerative Colitis as well.

‘Environmental’ in this sense means things that are outside the body — even if they can be eaten or absorbed. The study points out that there are three basic ways external factors can contribute to Crohn’s: 1) by making the gut leakier; 2) by changing the immune system in the gut; 3) by changing the gut microbiome.

The study discusses both how environmental factors help cause the disease, and also how they make the disease better or worse once a person already has it. In this post, we’re going to look only at the possible causes.

  • Hygiene — it’s hard to know how cleanly patients who get Crohn’s are, but several studies have looked at things like living in the city, hot water, and separate bathrooms, and found a correlation. However, “no single hygienic factor has demonstrate a consistent association with IBD.”
  • Air pollution — studies of animals show that air pollution can drive inflammation and change the gut microbiome. Studies of humans have shown “traffic-based pollutants” correlates to early-onset Crohn’s, and air pollution in general correlates to hospitalization.
  • Breastfeeding — breastfeeding is actually a protective factor, with studies showing it seems to help prevent Crohn’s, and other studies showing it seems to prevent early onset of both Crohn’s and Ulcerative Colitis.
  • Smoking — if air pollution correlates to Crohn’s, it makes sense that smoking would also. There are lots and lots of studies of how bad smoking is for people with Crohn’s.
  • Diet — various dietary factors are linked to IBD, but there is good evidence that dietary fiber from fruits and vegetables protects against developing Crohn’s, where eating omega-6 fatty acids (from some meats and vegetable oils) correlates to developing the disease.  (For a more comprehensive look at diet and IBD, see this previous post.)
  • Psychological factors — While stress is often believed to contribute to IBD, the scientific evidence is limited (more on that question in this previous post). Depression, anxiety, and sleep disturbance also show correlation to Crohn’s. Generally, though, there is not enough evidence to conclude that psychological factors help cause the disease.
  • Oral contraceptives — there is a “moderate association” between taking birth control and developing Crohn’s.
  • Non-steroidal Anti-inflammatory Drugs — use of NSAIDS like ibuprofen and aspirin put a person at greater risk for developing Crohn’s.
  • Antibiotics — there is evidence that “antibiotic use in early infancy and childhood confers a 3- to 5-fold increased risk of development” for Crohn’s in kids, and more generally for antibiotic use and the development of the disease.
  • Infections — frequent infections in childhood — including throat and lung infections — are associated with increased risk of Crohn’s in children. Two kinds of infection seem to have protective effects: H. pylori (a bacteria) and helminths (intestinal worms). There is mixed evidence for other infections, like MAP and measles, contributing to disease. Vaccines are not associated with the development of IBD.

Again, these are only the external risk factors; lots of folks are exposed to air pollution and don’t eat enough fiber and take birth control, and never get the disease. It also takes a genetic factor to lead to give a person Crohn’s disease.

Still, it is a good thing that medical science is beginning to understand how external factors contribute to the development of the disease, especially the ways those factors affect the body to make the disease emerge. Of course, more research is needed.

*The papers are Dam, A.N.; Berg, A.; Farraye, F. “Environmental Influences on the Onset and Clinical Course of Crohn’s Disease–Part 1: An Overview of External Risk Factors.” Gastroenterology & Hepatology 9:11 (Nov. 2013), and —- “Environmental Influences on the Onset and Clinical Course of Crohn’s Disease–Part 2: Infections and Medication Use.” Gastroenterology & Hepatology 9:12 (Dec. 2013).

Photo “Cigarette” by Flickr user Fried Dough used under Creative Commons license



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