Physical activity reduces mortality among colorectal cancer survivors and excessive television viewing increases it, according to a recent study published in the Journal of Clinical Oncology.1

“The takeaway message from our study is that both minimizing TV viewing, to less than 2 hours per day, and increasing exercise, to 4-plus hours per week, were associated with lower mortality risk among colorectal cancer survivors,” said study author Hannah Arem, PhD, MHS, a postdoctoral fellow with the National Cancer Institute’s Nutritional Epidemiological Branch.

The research team examined data previously collected in the National Institutes of Health–American Association of Retired Persons Diet and Health Study, which included more than half a million people age 50 to 71. In 1995 and 1996, participants completed surveys that included questions on their leisure time activity and television watching. Follow-up surveys were conducted in 2004 and 2005.

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The researchers identified 3,797 individuals with local or regional colorectal cancer. Lifestyle habits both before and after diagnosis had an effect on mortality in this group.

Subjects who reported 7 hours or more per week of moderate to strenuous physical activity before being diagnosed had a 20% lower risk of dying from any cause than survivors who reported no physical activity (hazard ratio [HR], 0.80; 95% CI: 0.68,0.95; P for trend=0.02). Their risk of colorectal cancer mortality was lower, but not significantly so (HR, 0.84; 95% CI:; P for trend=0.28).

By contrast, patients who reported that they watched 5 hours or more of television per day before diagnosis had a 22% higher risk of dying from any cause compared with those who watched less than 2 hours per day (HR, 1.22; 95% CI: 1.06,1.41; P for trend=0.002). Television viewing did not have a significant effect on colorectal cancer mortality.

Physical activity and television viewing after diagnosis of colorectal cancer had an even greater impact on mortality, especially when they were analyzed together.

Among 1,759 patients for whom post-diagnosis data were available, those who reported 7 hours or more per week of physical activity after their diagnosis had a 31% lower risk of all-cause mortality than those who reported no physical activity, independent of their prediagnosis physical activity (HR, 0.69; 95% CI: 0.49,0.98; P for trend=0.01). Patients who were highly active also had a 47% lower risk of colorectal cancer mortality, although this difference was not statistically significant (HR, 0.53; 95% CI: 0.27,1.03; P for trend=0.04).

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The effects of post-diagnosis television viewing were less clear-cut. There was a nonsignificant increase in all-cause mortality among patients who watched more than 4 hours of television per day after diagnosis compared those who watched 2 hours or less per day (HR, 1.25; 95% CI: 0.93,1.67; P for trend=0.13). There was no association between post-diagnosis television viewing and colorectal cancer mortality.

A joint analysis of post-diagnosis physical activity and television watching found that patients in the high physical activity/low television group had a 29% lower risk of all-cause mortality than those in the low physical activity/high television group (HR, 0.71; 95% CI: 0.50,0.99).

The researchers used television watching as a surrogate measure of sedentary behavior because it is the most prevalent leisure-time sedentary behavior, Dr. Arem said. Presumably, reading, surfing the internet, and other sedentary activities would have similar effects as television watching on survival among patients with colorectal cancer.


  1. Arem H, Pfeiffer RM, Engels EA, et al. Pre- and postdiagnosis physical activity, television viewing, and mortality among patients with colorectal cancer in the National Institutes of Health–AARP diet and health study. J Clin Oncol. 2014 Dec 8. [Epub ahead of print]. doi:10.1200/JCO.2014.58.1355.