Smoking and Crohn's Disease

The relationship between smoking and IBD is complex. In many studies, Crohn’s Disease is associated with smoking and the research suggests that smoking increases the severity of the disease. 


How does smoking affect Crohn’s Disease?



In numerous studies, half or more of adults diagnosed with Crohn’s Disease smoked at diagnosis. This suggests that people who smoke are more likely to get Crohn’s than those who do not smoke. Research also shows that smoking can make Crohn’s Disease worse. Smokers with Crohn’s in their small bowel are more 
likely to have more severe symptoms, to require stronger immunosuppressant drugs, and have a poorer quality of life.

This effect appears to be greater in women with Crohn’s who smoke. Another study found that smokers were twice as likely to have a flare up of Crohn’s when compared to non-smokers. Studies have suggested that smoking also reduces the effectiveness of certain treatments for Crohn’s, including the biological drug, infliximab. Smokers with Crohn’s in the small bowel have a greater chance of needing surgery than non-smokers.


If I am a smoker now, is it worth giving up?

Research strongly supports the notion that giving up smoking is beneficial for people with Crohn’s Disease. 
In the non-smoker, Crohn’s seems milder. Once you have stopped smoking for one year, the chances of a flare up are probably as low as someone with Crohn’s who has never smoked. Another study showed that people who continued to smoke were over twice as likely to have a flare compared to people who had 
stopped smoking. Smokers also appear to have a greater need for some of the stronger forms of medical treatment such as immunosuppressant drugs.

You are less likely to need repeat surgery if you stop smoking. There is no significant difference in surgery rates between ex-smokers and non-smokers after ten years. It may be tempting just to reduce the amount you smoke. However, research has found that even light smokers with Crohn’s Disease have a more active 
disease and greater hospitalisation rate. This suggests that completely stopping smoking has the most benefit.


What about the risk of passive smoking?

A study in the USA found that people with Crohn’s Disease were more likely to have had mothers who smoked during pregnancy, or to have been exposed to smoking at home during childhood. Another study in Scotland of children with IBD had similar findings regarding mothers smoking during pregnancy, or around the time of birth, although it did not find such a risk from passive smoking during childhood. Researchers in this study believed that it was the early exposure that was significant, smoking by either parent having a similar effect on their unborn baby.