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Do Certain Sedentary Behaviors Increase the Risk of Young-Onset Colorectal Cancer?

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Key Points

  • Although colorectal cancer rates in older adults have been decreasing in the United States since the mid-1980s, incidence rates for the cancer have been increasing among young and middle-aged adults.
  • More than 1 hour of daily TV viewing was associated with a 12% increased risk of young-onset colorectal cancer, particularly of the rectum. Watching more than 2 hours a day increased the risk to nearly 70%.
  • The study results may help identify those at high risk of developing young-onset colorectal cancer and who might benefit from early colorectal cancer screening.

Although colorectal cancer rates in older adults have been decreasing in the United States since the mid-1980s, incidence rates for the cancer have been increasing among young and middle-aged adults, according to a study by the American Cancer Society (ACS). Based on the new data, in 2018, the ACS updated its colorectal cancer screening guideline, lowering the recommended beginning screening age for people at average risk of colorectal cancer from age 50 to age 45.

The exact reasons for the rise in young-onset colorectal cancer are unknown, but a large prospective study is shedding light on potential risk factors. The study, which evaluated sedentary behaviors, primarily time watching television, and the risk of young-onset colorectal cancer has found that more than 1 hour of daily TV viewing was associated with a 12% increased risk of the cancer, particularly of the rectum, compared to those who watched less TV. Watching more than 2 hours a day had a nearly 70% increase in risk. The association was independent of body mass index (BMI) and family history of colorectal cancer. The study by Nguyen et al was published in JNCI Cancer Spectrum.

Study Methodology

The researchers collected data on the sedentary behaviors, including primarily television watching, among 89,278 women enrolled in the Nurses’ Health Study II. The women were aged 25 to 42 years at the time of recruitment from 1991 to 2011. In addition to TV viewing time, the researchers also evaluated the amount of time the women spent sitting at home reading, eating meals, and at a desk, as well as collective hours spent sitting at work and while driving.

The researchers used Cox proportional hazards modelling to estimate relative risks (RRs) and 95% confidence intervals (CIs). Statistical tests were two-sided.

Study Results

The researchers found of the 118 cases of young-onset colorectal cancer diagnosed over 22 years of follow-up, sedentary TV viewing time was statistically significantly associated with increased risk of young-onset colorectal cancer. After adjusting for putative risk factors, including obesity and physical activity, more than 1 hour of daily TV viewing time was associated with a 12% increase in risk compared to those who watched less TV.

For those who watched more than 2 hours of TV per day, there was a nearly 70% increase in risk, as follows: compared to women watching 7 or fewer hours of TV per week, women with 7.1 to 14 hours per week of TV time had a multivariable relative risk of 1.12 (95% CI = 0.72–1.75), with risk increasing among those reporting more than 14 hours of viewing time per week (RR = 1.69, 95% CI = 1.07–2.67; P = .03).

The association was observed among participants without a family history of colorectal cancer and was more pronounced for rectal cancer (RR for > 14 vs < 7 hours per week = 2.44; 95% CI = 1.03–5.78; P = .04). Participants who are overweight or obese may be more susceptible to developing the cancer, according to the findings.

The study found no clear increase in risk for other forms of sitting at home—such as meal time or time spent at a desk—or sitting away from home.

Benefit of Early Screening

“This study may help identify those at high risk [of colorectal cancer] and who might benefit more from early screening,” said Yin Cao, MPH, ScD, Assistant Professor of Surgery at Washington University School of Medicine, and a co–senior author of this study, in a statement. “The fact that these results were independent of BMI and physical activity suggests that being sedentary may be an altogether distinct risk factor for young-onset colorectal cancer.”

Disclosure: Funding for this study was provided by the National Institutes of Health, the Crohn’s and Colitis Foundation, National Research Foundation of Korea, Massachusetts General Hospital, and the Raymond P. Lavietes Foundation. The study authors' full disclosures can be found at academic.oup.com.

The content in this post has not been reviewed by the American Society of Clinical Oncology, Inc. (ASCO®) and does not necessarily reflect the ideas and opinions of ASCO®.


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