title: Association between constipation and colorectal cancer: systematic review and meta-analysis of observational studies.
abstract: OBJECTIVE
  Constipation is common in the community, and may affect survival adversely. An association between constipation and development of colorectal cancer (CRC) could be one possible explanation. We performed a systematic review and meta-analysis examining this issue.
  
  
  METHODS
  We searched MEDLINE, EMBASE, and EMBASE Classic (through July 2012). Eligible studies were cross-sectional surveys, cohort studies, or case-control studies reporting the association between constipation and CRC. For cross-sectional surveys and cohort studies, we recorded number of subjects with CRC according to the constipation status, and for case-control studies, number of subjects with constipation according to CRC status were recorded. Study quality was assessed according to published criteria. Data were pooled using a random effects model, and the association between CRC and constipation was summarized using an odds ratio (OR) with a 95% confidence interval (CI).
  
  
  RESULTS
  The search strategy identified 2,282 citations, of which 28 were eligible. In eight cross-sectional surveys, presence of constipation as the primary indication for colonoscopy was associated with a lower prevalence of CRC (OR=0.56; 95% CI 0.36-0.89). There was a trend toward a reduction in odds of CRC in constipation in three cohort studies (OR=0.80; 95% CI 0.61-1.04). The prevalence of constipation in CRC was significantly higher than in controls without CRC in 17 case-control studies (OR=1.68; 95% CI 1.29-2.18), but with significant heterogeneity, and possible publication bias.
  
  
  CONCLUSIONS
  Prospective cross-sectional surveys and cohort studies demonstrate no increase in prevalence of CRC in patients or individuals with constipation. The significant association observed in case-control studies may relate to recall bias.
authors.affiliation: Leeds Gastroenterology Institute, St. James's University Hospital, Leeds, UK.
authors.forename: Andrew M
authors.initials: AM
authors.lastname: Power
authors.forename: Nicholas J
authors.initials: NJ
authors.lastname: Talley
authors.forename: Alexander C
authors.initials: AC
authors.lastname: Ford
mesh_terms: D015331:Cohort Studies; D015179:Colorectal Neoplasms / Q000453:epidemiology*; D015897:Comorbidity; D016001:Confidence Intervals; D003248:Constipation / Q000453:epidemiology*; D003430:Cross-Sectional Studies; D006801:Humans; D016017:Odds Ratio; D015995:Prevalence