title: Lifestyle factors and colorectal cancer risk (2): a systematic review and meta-analysis of associations with leisure-time physical activity.
abstract: OBJECTIVE
  Increased physical activity may decrease the risk of colorectal cancer. As a prerequisite to the determination of lifestyle attributable risks, we performed a systematic review and meta-analysis of prospective observational studies to quantify gender-specific risk associated with increased leisure-time physical activity (LT-PA).
  
  
  METHODS
  We searched MEDLINE and EMBASE (to December 2007), and other sources, selecting reports based on strict inclusion criteria. We used random-effects meta-analyses to estimate summary risk ratios (RR) and 95% confidence intervals (95% CI) for uppermost vs lowermost categories of physical activity. To investigate dose-response, we explored risks ratios as a function of cumulative percentiles of physical activity distribution.
  
  
  RESULTS
  Fifteen datasets from 14 articles, including 7873 incident cases, were identified. For colon cancer, there were inverse associations with LT-PA for men (RR: 0.80; 95% CI: 0.67-0.96) and women (0.86; 0.76-0.98). LT-PA did not influence risk of rectal cancer. The dose-response analysis was consistent with linear pattern reductions in risk of colon cancer in both genders. There was evidence of moderate between-study heterogeneity but summary estimates were broadly consistent across potential confounding factors.
  
  
  CONCLUSIONS
  Increased LT-PA is associated with a modest reduction in colon but not rectal cancer risk; a risk reduction, which previously may have been overstated. LT-PA only interventions in public health cancer prevention strategies are unlikely to impact substantially on colorectal cancer incidences.
authors.affiliation: Research Institute for Sport and Exercise Sciences, Liverpool John Moores University, Liverpool, UK.
authors.forename: D J
authors.initials: DJ
authors.lastname: Harriss
authors.forename: G
authors.initials: G
authors.lastname: Atkinson
authors.forename: A
authors.initials: A
authors.lastname: Batterham
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: A G
authors.initials: AG
authors.lastname: Renehan
mesh_terms: D015992:Body Mass Index; D003110:Colonic Neoplasms / Q000517:prevention & control*; D005260:Female; D006801:Humans; D007899:Leisure Activities; D008297:Male; D016017:Odds Ratio; D012004:Rectal Neoplasms / Q000517:prevention & control*; D040242:Risk Reduction Behavior; D012737:Sex Factors