title: Timing and intensity of recreational physical activity and the risk of subsite-specific colorectal cancer.
abstract: OBJECTIVE
  Although there is convincing evidence that physical activity reduces colon cancer risk, there are important questions that remain unanswered about the association. These include the timing and intensity of activity required to optimally reduce risk, and whether physical activity has a different effect on cancers at different sites within the colon. We conducted a case-control study to investigate these issues.
  
  
  METHODS
  A case-control study of colorectal cancer was conducted in Western Australia in 2005-2007. Data were collected on various risk factors. The estimated effects of recreational physical activity on the risk of cancers of the distal colon, proximal colon, and rectum were analyzed using multinomial logistic regression. This analysis included 870 cases and 996 controls.
  
  
  RESULTS
  The risk of distal colon cancer was reduced by performing a high level of vigorous-intensity activity between the ages 19 and 34 years (women), 35 and 50 years (men), after the age of 51 years (men and women), and consistently over the adult lifetime (men and women). The risk of rectal cancer was reduced by performing a high level of vigorous activity between the ages 35 and 50 years (men), and consistently over the adult lifetime (men). Proximal colon cancer risk was not associated with physical activity in any of the age periods or over the adult lifetime. Moderate intensity activity did not reduce the risk of colorectal cancer.
  
  
  CONCLUSIONS
  Physical activity may have a greater effect on the risk of distal colon cancer than proximal colon cancer. Vigorous physical activity is required to reduce colorectal cancer risk.
authors.affiliation: School of Population Health, The University of Western Australia, Perth, WA, Australia. tboyle@waimr.uwa.edu.au
authors.forename: Terry
authors.initials: T
authors.lastname: Boyle
authors.forename: Jane
authors.initials: J
authors.lastname: Heyworth
authors.forename: Fiona
authors.initials: F
authors.lastname: Bull
authors.forename: Sarah
authors.initials: S
authors.lastname: McKerracher
authors.forename: Cameron
authors.initials: C
authors.lastname: Platell
authors.forename: Lin
authors.initials: L
authors.lastname: Fritschi
mesh_terms: D000230:Adenocarcinoma / Q000453:epidemiology* / Q000473:pathology*; D000328:Adult; D016022:Case-Control Studies; D015179:Colorectal Neoplasms / Q000453:epidemiology* / Q000473:pathology*; D015444:Exercise / Q000502:physiology*; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D012307:Risk Factors; D055815:Young Adult