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7 Study Exploration: Smoking and How it is Linked in Crohn's Disease

Exposure to cigarette smoke, whether first- or second-hand, is a risk factor for Crohn's disease. Regular smokers especially are more likely to develop Crohn's. Smoking is seen as an independent risk factor of developing Crohn's disease. Smoking as an independent risk factor has become known through seven main studies which have been published in the Journal of Crohn's and Colitis.

In this article, we will be exploring those seven studies and the information they provide for understanding the link between Crohn's disease and smoking. Let's get started...

1. The Role of Smoking and Crohn's Diagnosis

The first study found that people who are diagnosed with Crohn's disease are more likely to smoke compared to others who are not diagnosed with Crohn's disease. It was found to be especially strong within three months of being diagnosed with Crohn's disease.

2. Type of Smoker and the Active Level of Crohn's Disease

The second study was conducted in France. With approximately 3,000 participants, the study looked at:

Smoking level of participants:

  • Non-smoker
  • Light smoker (1-10 cigarettes)
  • Heavy smoker (10 and more cigarettes a day)

Percentage of time spent living with active Crohn's disease:

  • Non-smokers: 33%
  • Light smokers: 38%
  • Heavy smokers: 41%

Percentage of time exposed and consumption of immunosuppressants:

  • Non-smokers: 32%
  • Light smokers: 34%
  • Heavy smokers: 36%

Are you wondering how immunosuppressants help treat Crohn's disease?

3. The Need for Immunosuppressive Drugs and Biologic Therapy to Maintain Remission

Immunosuppressants are to by some who have Crohn's disease for reducing inflammation caused by substances within the immune system. A third study where 1,170 participants were surveyed further confirmed smoking as an independent risk factor for the development of Crohn's disease and its impact on maintaining the disease in a state of remission.

What was found was smokers have a higher need to choose treatment with immunosuppressants to obtain and maintain a state of remission over non-smokers who may reach a state of remission through diet and other supportive treatment options.

4. Smoking Escalates the Starting Grade level of Crohn's Disease

The fourth study had 3224 participants and was completed in Spain. One of the discoveries it made was the connection between smoking and the stating grade level of Crohn's disease at diagnosis. The grading scale is used was based on the Montreal grading scale:

The Montreal classification of inflammatory bowel disease: Crohn's Disease:

This is what the third study found:

Percentage of people with Crohn's disease with moderate or B1 level Crohn's disease:

  • Non-smokers: 19.3%
  • Smokers: 22.5 %

5. Smoking Increases the Likelihood of Crohn's Disease Grading Change

The fifth study has 506 participants and examined the relationship between the chance of going up in the Montreal grading scale for active Crohn's disease for non-smokers versus smokers. The study found that continuing to smoke after being diagnosed with Crohn's disease or picking up the habit of smoking after diagnosis raised the chances of Crohn's disease active grade level increase from B1 to B2 or even a B3.

The ratio odds ratio of the grading scale increase in relation to smokers vs. non-smokers was 2.02.

6. Smoking Increases the Likelihood of Surgery with Crohn's Disease

The sixth study researched and explored increase likelihood of non-smokers versus smokers who living with Crohn's disease and their need for intestinal surgery. The study followed 174 participants over the course of 10 years. This is what was found:

Smokers have a 29% higher chance of needing intestinal surgery because of Crohn's disease compared to those who do not smoke.

7. Smoking Impacts the Effectiveness of Medical Treatment for Crohn's Disease

A seventh study found that there are correlations and connections between non-smokers and smokers in their ability to be receptive and respond positively to medical treatment.

Here is what the seventh study found:

Percentage of people with Crohn's disease who positively respond to the episodic use of the drug infliximab with moderate or B1 level Crohn's disease:

  • Non-smokers: 73%
  • Smokers: 22%


Parkes, C., G., Whelan, Kevin, Lindsay, & O., J. (2014, August 01). Smoking in inflammatory bowel disease: Impact on disease course and insights into the aetiology of its effect. Retrieved December 11, 2018, from

Satsangi, J., Silverberg, M. S., Vermeire, S., & Colombel, J. F. (2006, June). The Montreal classification of inflammatory bowel disease: Controversies, consensus, and implications. Retrieved December 11, 2018, from