title: Is smoking an indirect risk factor for the development of ulcerative colitis? An age- and sex-matched case-control study.
abstract: BACKGROUND
  It has been suggested that smoking protects against the development of ulcerative colitis (UC). Evidence is mainly driven from the way data from a multitude of case-control studies have been interpreted.
  
  
  METHODS
  An age- and sex-matched case-control study was conducted to further assess the association between history of smoking, past surgery, childhood, and other potential causative factors with the development of UC using the answers to a detailed questionnaire. The data were analyzed using univariate analysis and logistic regression. The results are presented as odds ratios (OR) and 95% confidence intervals.
  
  
  RESULTS
  One hundred and two cases and an equal number of matched controls were included in the study. Using a three-level comparison, at the age of diagnosis, the risks of developing UC were 0.41 (0.19-0.87), 3.45 (1.62-7.35) and 0.78 (0.44-1.37) for smokers, ex-smokers and non-smokers, respectively. When compared to individuals who have never smoked, ex-smokers were at a higher risk of developing the disease (OR = 3.00 (1.38-6.51)). The specific history of quitting smoking prior to the age of onset of symptoms was associated with an increased risk for developing the disease (OR = 3.45 (1.62-7.35)).
  
  
  CONCLUSIONS
  Active smoking was associated with a low risk for the development of UC, but the lack of history of smoking was not associated with an increase in the risk. History of quitting smoking prior to the onset of symptoms, in contrast, was associated with a significant increase in the risk of developing the disease. These findings make the theory of a simple protective effect of smoking on the development of UC difficult to justify. It may be plausible to suggest that the withdrawal of the immunosuppressive effect of smoking triggers the disease onset in a genetically susceptible individual or simply unmasks its symptoms.
authors.affiliation: Department of Colorectal Surgery, University of Sydney and Royal Prince Alfred Hospital, Sydney, Australia.
authors.forename: Ned
authors.initials: N
authors.lastname: Abraham
authors.forename: Warwick
authors.initials: W
authors.lastname: Selby
authors.forename: Ross
authors.initials: R
authors.lastname: Lazarus
authors.forename: Michael
authors.initials: M
authors.lastname: Solomon
mesh_terms: D000293:Adolescent; D000328:Adult; D000367:Age Factors; D017668:Age of Onset; D000368:Aged; D000369:Aged, 80 and over; D016022:Case-Control Studies; D002648:Child; D003093:Colitis, Ulcerative / Q000453:epidemiology / Q000209:etiology*; D016001:Confidence Intervals; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D016017:Odds Ratio; D012044:Regression Analysis; D012307:Risk Factors; D017678:Sex Distribution; D012907:Smoking / Q000009:adverse effects*