title: Diabetes mellitus and the incidence of colorectal cancer: an updated systematic review and meta-analysis.
abstract: OBJECTIVE
  The purpose of this study was to determine whether diabetes mellitus is associated with an increased risk of colorectal cancer.
  
  
  METHODS
  Relevant studies were identified in MEDLINE and EMBASE (up until November 1st, 2011). Inclusion criteria were original, peer-reviewed publications, with case-control and cohort studies (for studies on diabetes mellitus and colorectal cancer). Summary relative risks with 95% confidence intervals were calculated with a random-effects model.
  
  
  RESULTS
  Twenty-four studies including eight case-control and 16 cohort studies, with a total of 3,659,341 participants, were included in this updated systematic review and meta-analysis, and all involved diabetes mellitus and colorectal cancer risk. Meta-analysis of the 24 included studies indicated that diabetes was associated with an increased risk of colorectal cancer, compared with no diabetes (summary RR of colorectal cancer incidence = 1.26, 95% CI = 1.20-1.31), without heterogeneity between studies (P(heterogeneity) = 0.296). Sub-group analyses found that these results were consistent between case-control and cohort studies and among studies conducted in different areas. The association between diabetes and colorectal cancer incidence did not differ significantly by sex and sub-sites. Insulin therapy was also positively associated with risk of colorectal cancer (summary RR = 1.61, 95% CI 1.18-1.35), with evidence of heterogeneity between studies (P(heterogeneity) = 0.014).
  
  
  CONCLUSIONS
  Our findings further support a relationship between diabetes and increased risk of colon and rectal cancer in both women and men, and insulin therapy for diabetes may increase this risk.
authors.affiliation: Division of Gastrointestinal Surgery, Department of General Surgery, First Affiliated Hospital, Nanjing Medical University, Nanjing, People's Republic of China.
authors.forename: Longying
authors.initials: L
authors.lastname: Deng
authors.forename: Zhifu
authors.initials: Z
authors.lastname: Gui
authors.forename: Lianying
authors.initials: L
authors.lastname: Zhao
authors.forename: Jianping
authors.initials: J
authors.lastname: Wang
authors.forename: Lizong
authors.initials: L
authors.lastname: Shen
mesh_terms: D017677:Age Distribution; D000368:Aged; D000369:Aged, 80 and over; D016022:Case-Control Studies; D002681:China / Q000453:epidemiology; D015331:Cohort Studies; D015179:Colorectal Neoplasms / Q000175:diagnosis / Q000453:epidemiology* / Q000628:therapy; D015897:Comorbidity; D003922:Diabetes Mellitus, Type 1 / Q000175:diagnosis / Q000453:epidemiology* / Q000628:therapy; D003924:Diabetes Mellitus, Type 2 / Q000175:diagnosis / Q000453:epidemiology* / Q000628:therapy; D005260:Female; D006801:Humans; D015994:Incidence; D008297:Male; D008875:Middle Aged; D011379:Prognosis; D017678:Sex Distribution; D016019:Survival Analysis