title: Lifestyle factors and colorectal cancer risk (1): systematic review and meta-analysis of associations with body mass index.
abstract: OBJECTIVE
  Excess body weight, defined by body mass index (BMI), may increase the risk of colorectal cancer. As a prerequisite to the determination of lifestyle attributable risks, we undertook a systematic review and meta-analysis of prospective observational studies to quantify colorectal cancer risk associated with increased BMI and explore for differences by gender, sub-site and study characteristics.
  
  
  METHODS
  We searched MEDLINE and EMBASE (to December 2007), and other sources, selecting reports based on strict inclusion criteria. Random-effects meta-analyses and meta-regressions of study-specific incremental estimates were performed to determine the risk ratio (RR) and 95% confidence intervals (CIs) associated with a 5 kg/m(2) increase in BMI.
  
  
  RESULTS
  We analysed 29 datasets from 28 articles, including 67,361 incident cases. Higher BMI was associated with colon (RR 1.24, 95% CIs: 1.20-1.28) and rectal (1.09, 1.05-1.14) cancers in men, and with colon cancer (1.09, 1.04-1.12) in women. Associations were stronger in men than in women for colon (P < 0.001) and rectal (P = 0.005) cancers. Associations were generally consistent across geographic populations. Study characteristics and adjustments accounted for only moderate variations of associations.
  
  
  CONCLUSIONS
  Increasing BMI is associated with a modest increased risk of developing colon and rectal cancers, but this modest risk may translate to large attributable proportions in high-prevalence obese populations. Inter-gender differences point to potentially important mechanistic differences, which merit further research.
authors.affiliation: Research Institute for Sport and Exercise Sciences, Liverpool John Moores University, Henry Cotton Campus, Liverpool, UK.
authors.forename: D J
authors.initials: DJ
authors.lastname: Harriss
authors.forename: G
authors.initials: G
authors.lastname: Atkinson
authors.forename: K
authors.initials: K
authors.lastname: George
authors.forename: N Tim
authors.initials: NT
authors.lastname: Cable
authors.forename: T
authors.initials: T
authors.lastname: Reilly
authors.forename: N
authors.initials: N
authors.lastname: Haboubi
authors.forename: M
authors.initials: M
authors.lastname: Zwahlen
authors.forename: M
authors.initials: M
authors.lastname: Egger
authors.forename: A G
authors.initials: AG
authors.lastname: Renehan
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D015992:Body Mass Index; D003110:Colonic Neoplasms; D005260:Female; D006801:Humans; D008019:Life Style; D008297:Male; D008875:Middle Aged; D009765:Obesity / Q000150:complications*; D016017:Odds Ratio; D012307:Risk Factors; D012737:Sex Factors; D055815:Young Adult