New study shows sitting, watching TV linked to colorectal cancer risk before age 50

A new study in JNCI Cancer Spectrum has identified a connection between prolonged time spent sitting while watching TV and increased risk of colorectal cancer for younger Americans.

Young-onset colorectal cancer, diagnosed under age 50, is increasing in the U.S. and globally, sharply contrasting with the dramatic decreases among older people, largely as a result of cancer screening initiatives. Young-onset colorectal cancer has potentially different molecular characteristics compared to those of late-onset, and is typically more aggressive and found at a more advanced stage than those in older patients, resulting in greater years of life lost. Despite these trends, researchers have identified few risk factors specific to young-onset colorectal cancer.

Researchers here studied sedentary TV reviewing time, as well as other sedentary behaviors, in 89,278 American women in the Nurses’ Health Study II. Of the 118 cases of young-onset colorectal cancer diagnosed over two decades of follow up, more than one hour of daily TV viewing time was associated with a 12 percent increase in risk compared to those who watched less. The results were even more striking for those watching more than two hours per day, with a nearly 70 percent increase in risk. This association was independent of BMI (body mass index) and exercise and was consistently observed among women without a family history of colorectal cancer. The association was also more pronounced for rectal cancer compared to colon cancer.

These findings are among the first to link specific sedentary behavioral patterns with risk of young-onset colorectal cancer. “This study may help identify those at high risk and who might benefit more from early screening,” said the study’s co-senior author, Yin Cao, ScD, an assistant professor of surgery at Washington University School of Medicine in St. Louis and a research member of Siteman Cancer Center. “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.”

The paper, “Sedentary Behaviors, TV Viewing Time, and Risk of Young-Onset Colorectal Cancer,” is available at: https://pubmed.ncbi.nlm.nih.gov/30740587/.