Skip to content
View commentaries on this research

This is a plain English summary of an original research article

Non-smokers and people who stop smoking after being diagnosed with ulcerative colitis are unlikely to have more flare-ups or other signs of worsening disease, compared with those who continue to smoke.

Smoking is linked to reduced rates of developing ulcerative colitis in some studies. Some patients also believe that smoking can also lessen the symptoms of the disease, although previous research about this has had conflicting results. This study indicates that smoking does not have a significant effect on the illness after diagnosis.

Researchers followed 6,754 UK adults diagnosed with ulcerative colitis for 12 years. They compared outcomes for former smokers, non-smokers and smokers, and for people who stopped smoking after diagnosis. After adjusting for other factors, they found similar rates of corticosteroid use, flare-ups, hospital admissions and colectomy (surgical removal of all or part of the large bowel), regardless of smoking status.

People with ulcerative colitis can be encouraged to stop smoking, for the usual health-related reasons.

Why was this study needed?

Ulcerative colitis causes inflammation and ulceration of the colon and rectum. It is thought to affect about 1 in 420 people in the UK. Some observational studies have suggested that people who smoke are less likely to develop ulcerative colitis than people who do not smoke, or who used to smoke. It is unclear why this is.

Previous evidence looking at the effect of smoking on people with ulcerative colitis has been inconclusive. A meta-analysis of 16 studies from 2016 found no evidence that smoking reduced disease progression or flares. However, other studies – which tended to focus on specialist services, did find an effect. Some people with ulcerative colitis believe smoking helps their symptoms and continue to smoke, for this reason, risking other poor health outcomes from tobacco use.

This study was designed to evaluate the effect of both smoking status and smoking cessation on disease outcomes for people with ulcerative colitis, treated in the community or specialist services.

What did this study do?

Researchers identified a cohort of people with the first diagnosis of ulcerative colitis during the period between 1 January 2005 and 30 April 2016. They were identified from the Clinical Practice Research Datalink (CPRD), a large UK general practice database. Researchers recorded their smoking status before diagnosis and any change after that.

Researchers used the CPRD and the Hospital Episode Statistics (HES) database to record outcomes including oral corticosteroid use, other medication for ulcerative colitis, hospital admissions and colectomy.

They calculated the risk of these outcomes by smoking status and smoking cessation, adjusting their figures to account for sex, age at diagnosis, use of the anti-inflammatory drug 5-aminosalicylic acid, deprivation and period of diagnosis (in 2-year periods).

What did it find?

  • The study included 9,616 people with the first diagnosis of ulcerative colitis, 6,754 of whom had their smoking status recorded at the time of diagnosis. Around 40% had never smoked, 47% were former smokers, and 13% were current smokers. The proportion of smokers remained constant throughout the 12-year study period, in contrast to a decline in smoking rates in the general population.
  • The cumulative rates of oral corticosteroid use at one, three and five years among smokers and ex-smokers were similar to the rates for non-smokers (27.9%, 34.8% and 37.1%).
  • The risk of a flare of symptoms requiring corticosteroid use was similar among smokers, compared with never smokers (odds ratio [OR] 1.16, 95% confidence interval [CI] 0.92 to 1.46), and among former smokers compared with never smokers (OR 1.07, 95% CI 0.92 to 1.25).
  • Smoking status was not linked to hospitalisation (hazard ratio [HR] for smokers compared with never smokers HR 0.92, 95% CI 0.72 to 1.18).
  • The rate of colectomy (around 9%) was similar in smokers compared with non-smokers (HR 0.78, 95% CI 0.50 to 1.21).

What does current guidance say on this issue?

NICE published a guideline on the management of ulcerative colitis in May 2019. The guideline does not mention smoking or smoking cessation in its recommendations.

What are the implications?

The risks to health of tobacco smoking are well-known, and advice to all smokers remains that these risks outweigh any potential benefits.

This study did not find any evidence to support the theory that smoking can reduce disease activity in ulcerative colitis, or that smoking has benefits for people with ulcerative colitis.

People with ulcerative colitis who smoke can be encouraged to stop, without it influencing their colitis.

Citation and Funding

Blackwell J, Saxena S, Cecil E et al. The impact of smoking and smoking cessation on disease outcomes in ulcerative colitis: a nationwide population‐based study. Aliment Pharmacol Ther. 2019;50:556–67.

This project was supported by the NIHR School for Public Health Research, the Wellcome Trust and Crohn’s and Colitis UK.



NICE. Ulcerative colitis: management. NG130. London: National Institute for Health and Care Excellence; 2019.

Dignass A, Eliakim R, Magro F et al. Second European evidence-based consensus on the diagnosis and management of ulcerative colitis part 1: definitions and diagnosis. J Crohn's Colitis. 2012;6(10):965-90.

Lunney PC and Leong RWL. Review article: ulcerative colitis, smoking and nicotine therapy. Aliment Pharmacol Ther. 2012;36,997-1008.

Magro F, Gionchetti P, Eliakim R et al. Third European evidence-based consensus on diagnosis and management of Ulcerative Colitis. Part 1: Definitions, diagnosis, extra-intestinal manifestations, pregnancy, cancer surveillance, surgery, and ileo-anal pouch disorders. J Crohn’s Colitis. 2017;11:649-70.

Produced by the University of Southampton and Bazian on behalf of NIHR through the NIHR Dissemination Centre


  • Share via:
  • Print article
Back to top