title: Physical activity, sedentary behavior, and the risk of colon and rectal cancer in the NIH-AARP Diet and Health Study.
abstract: OBJECTIVE
  In order to prospectively investigate physical activity at varying intensities and sedentary behavior in relation to colorectal cancer.
  
  
  METHODS
  We considered 488,720 participants of the NIH-AARP Diet and Health Study who were aged 50-71 years at baseline in 1995-1996. Through 31 December, 2003, we identified 3,240 and 1,482 colorectal cancers among men and women, respectively. We estimated multivariable relative risks (RR) and 95% confidence intervals (CI) of colorectal cancer using Cox regression.
  
  
  RESULTS
  Engaging in exercise/sports five or more times per week compared to never or rarely exercising was associated with a reduced risk of colon cancer among men (p = 0.001; RR = 0.79, 95% CI = 0.68-0.91) and a suggestive decrease in risk among women (p = 0.376; RR = 0.85, 95% CI = 0.70-1.04). Engaging in exercise/sports was also associated with a decreased risk of rectal cancer in men (P = 0.074; RR comparing extreme categories = 0.76, 95% CI = 0.61-0.94). In men, we observed inverse relations of both low intensity (p = 0.017; RR = 0.81, 95% CI = 0.65-1.00 for > or =7 h/week) and moderate to vigorous intensity activity (p = 0.037; RR = 0.82, 95% CI = 0.67-0.99 for > or =7 h/week) to colon cancer risk. In contrast, sedentary behavior (time spent watching television/videos) was positively associated with colon cancer (p < 0.001; RR = 1.61, 95% CI = 1.14-2.27 for > or =9 h/day) among men. Similar, but less pronounced relations were observed in women.
  
  
  CONCLUSIONS
  Engaging in physical activity of any intensity is associated with reductions in colon and rectal cancer risk. Conversely, time spent sedentary is associated with increased colon cancer risk.
authors.affiliation: Division of Cancer Epidemiology and Genetics, Radiation Epidemiology Branch, National Cancer Institute, NIH, DHHS, Bethesda, MD, 20892, USA. reganho@mail.nih.gov
authors.forename: Regan A
authors.initials: RA
authors.lastname: Howard
authors.forename: D Michal
authors.initials: DM
authors.lastname: Freedman
authors.forename: Yikyung
authors.initials: Y
authors.lastname: Park
authors.forename: Albert
authors.initials: A
authors.lastname: Hollenbeck
authors.forename: Arthur
authors.initials: A
authors.lastname: Schatzkin
authors.forename: Michael F
authors.initials: MF
authors.lastname: Leitzmann
mesh_terms: D000368:Aged; D003110:Colonic Neoplasms / Q000453:epidemiology*; D015444:Exercise; D005260:Female; D005500:Follow-Up Studies; D015438:Health Behavior; D006306:Health Surveys; D006801:Humans; D008297:Male; D008875:Middle Aged; D016017:Odds Ratio; D012004:Rectal Neoplasms / Q000453:epidemiology*