- According to 20 years of data from the Nurses' Health Study II, increased weekly television viewing time is significantly associated with greater incidence of young-onset colorectal cancer (CRC), particularly rectal cancer
- The association was independent of traditional CRC risk factors, including physical activity and obesity
- Still, the risk of young-onset CRC was greater in subgroups defined by high body mass index, less physical activity or a history of smoking
- These findings provide further evidence of the need to encourage an active lifestyle, including minimal television viewing
Adults between the ages of 20 and 49 are showing a dramatic increase in the incidence of colorectal cancer (CRC) in the United States, parts of Europe and Asia. This is true even though overall CRC rates are decreasing. Even more alarming, young-onset CRC is less likely than conventional CRC to be detected before it reaches an advanced stage.
To help avoid delays in diagnosis, it is crucial to identify risk factors for young-onset CRC. Andrew T. Chan, MD, MPH, director of the Gastroenterology Training Program and a physician at the Mass General Cancer Center, and colleagues report in JNCI Cancer Spectrum that increased television viewing time is significantly associated with greater incidence of young-onset CRC, particularly rectal cancer.
Data from Nurses' Health Study II
The researchers examined data on 89,278 women from the Nurses' Health Study II (NHS II), with 118 of those women having developed young-onset CRC during the study period (1991–2011). Key exclusion criteria included a prior diagnosis of CRC or another cancer (except non-melanoma skin cancer), or inflammatory bowel disease before or during the study.
Nurses' Health Study II is a prospective cohort study of 116,430 female nurses who were 25 to 42 years old at enrollment in 1989. Every two years, they complete detailed questionnaires about their lifestyles and health status. In 1991, the NHS II researchers began collecting information on sedentary behaviors, including television viewing, which is watching any form of media on a television screen, including television broadcasts, videotapes and DVDs.
Quantifying the Risk
Prolonged sedentary television viewing was associated with significantly increased risk of young-onset CRC even after Dr. Chan's group adjusted for putative CRC risk factors, including inactivity and high body mass index (BMI).
Specifically, women who watched television for a moderate amount of time (7.1 to 14 hours/week) had a 12% higher risk of young-onset CRC than those who watched for ≤7 hours/week. Those who watched for an excessive amount of time (>14 hours/week) had a 69% higher risk.
Subgroup analyses by anatomic site showed that television viewing especially influenced the chance of developing young-onset rectal cancer. The risk was elevated by 91% for moderate watching and 2.4-fold for excessive watching.
The researchers evaluated differences in the association between sedentary TV viewing time and young-onset CRC according to subgroups defined by measures of an unhealthy lifestyle. Women who were overweight or obese, those who engaged in little physical activity and those who were smokers or former smokers had elevated risk of young-onset CRC compared with their healthier counterparts.
What About Other Screens?
The researchers did not study time spent with personal computers, tablets or smartphones because use of those devices was less common than television viewing between 1991 and 2011. Furthermore, there are some distinctions between television viewing time and other screen time:
- The newer devices are often used away from home
- Playing video games may involve more energy expenditure than watching television
- While watching television broadcasts, people are exposed to ads for unhealthy food
The American Cancer Society now recommends that routine screening for CRC should begin at age 45, rather than age 50. Currently, government data shows only 62% compliance with the earlier screening guideline.
The researchers conclude that their findings are further evidence of the need to encourage patients to maintain an active lifestyle, including minimizing television viewing time and to be screened at an earlier age.
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