title: Association between physical activity and mortality among breast cancer and colorectal cancer survivors: a systematic review and meta-analysis.
abstract: BACKGROUND
  Physical activity improves physical function during and after cancer treatment, but whether physical activity imparts survival benefit remains uncertain.
  
  
  METHODS
  Using prospective studies published through June 2013, we conducted a systematic review and random-effects meta-analysis of pre- and post-diagnosis physical activity in relation to total and cancer mortality among breast or colorectal cancer survivors.
  
  
  RESULTS
  Sixteen studies of breast cancer survivors and seven studies of colorectal cancer survivors yielded 49095 total cancer survivors, including 8129 total mortality cases and 4826 cancer mortality cases. Comparing the highest versus lowest levels of pre-diagnosis physical activity among breast cancer survivors, the summary relative risks (RRs) of total and breast cancer mortality were 0.77 [95% confidence interval (CI) = 0.69-0.88] and 0.77 (95% CI = 0.66-0.90, respectively. For post-diagnosis physical activity, the summary RRs of total and breast cancer mortality were 0.52 (95% CI = 0.42-0.64) and 0.72 (95% CI = 0.60-0.85), respectively. For pre-diagnosis physical activity among colorectal cancer survivors, the summary RRs of total and colorectal cancer mortality were 0.74 (95% CI = 0.63-0.86) and 0.75 (95% CI = 0.62-0.91), respectively. For post-diagnosis physical activity, the summary RRs of total and colorectal cancer mortality were 0.58 (95% CI = 0.48-0.70) and 0.61 (95% CI = 0.40-0.92), respectively. Each 10 metabolic equivalent task-hour/week increase in post-diagnosis physical activity (equivalent to current recommendations of 150 min/week of at least moderate intensity activity) was associated with 24% (95% CI = 11-36%) decreased total mortality risk among breast cancer survivors and 28% (95% CI = 20-35%) decreased total mortality risk among colorectal cancer survivors. Breast or colorectal cancer survivors who increased their physical activity by any level from pre- to post-diagnosis showed decreased total mortality risk (RR = 0.61; 95% CI = 0.46-0.80) compared with those who did not change their physical activity level or were inactive/insufficiently active before diagnosis.
  
  
  CONCLUSIONS
  Physical activity performed before or after cancer diagnosis is related to reduced mortality risk among breast and colorectal cancer survivors.
authors.affiliation: Department of Epidemiology and Preventive Medicine, University of Regensburg, Regensburg, Germany. Electronic address: daniela.schmid@klinik.uni-regensburg.de.
authors.forename: D
authors.initials: D
authors.lastname: Schmid
authors.affiliation: Department of Epidemiology and Preventive Medicine, University of Regensburg, Regensburg, Germany.
authors.forename: M F
authors.initials: MF
authors.lastname: Leitzmann
mesh_terms: D001943:Breast Neoplasms / Q000503:physiopathology*; D015179:Colorectal Neoplasms / Q000503:physiopathology*; D005260:Female; D006801:Humans; D008297:Male; D009043:Motor Activity; D017741:Survivors
keywords: cancer; meta-analysis; physical activity; survival