Colorectal cancer: TV viewing tied to risk of early onset

Recent research has linked prolonged sitting while viewing TV to a raised risk of developing colorectal cancer before the age of 50 years.

This effect, which appeared to be strongest for cancer that starts in the rectum, was independent of exercise and body mass index (BMI).

When they diagnose colorectal cancer in people younger than 50 years, doctors generally refer to it as young-onset colorectal cancer.

The recent study, which now features in the journal JNCI Cancer Spectrum, is one of the first to link a particular sedentary behavior to a higher risk of young-onset colorectal cancer.

While others have already suggested that prolonged sitting while viewing TV could be a risk factor for colorectal cancer, they have not looked specifically at young-onset colorectal cancer.

The researchers behind the new study note that young-onset colorectal cancer is usually more aggressive than colorectal cancer that strikes later in life and is likely to have some distinct biological features.

Also, by the time diagnosis takes place, the cancer is usually more advanced, resulting in poorer rates of survival.

Senior study author Dr. Yin Cao, who is an assistant professor in the Department of Surgery at Washington University School of Medicine in St. Louis, MO, suggests that the new finding “may help identify those at high risk and who might benefit more from early screening.”

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Cancer of the colon and the rectum

Colorectal cancer is cancer that starts in the colon or the rectum, which together form the final section of the gut at the opposite end to the mouth, food pipe, and stomach.

With the help of bacteria, the colon breaks down undigested food and extracts water and salts from it.

The remains of that final stage of digestion then move into the rectum, which holds the waste pending evacuation through the anus in the form of stools.

In the majority of cases, colorectal cancer arises from small growths, or polyps, that form in the lining of that part of the gut.

It can take many years for polyps to turn into tumors, and not all polyps become cancerous.

The extent to which the tumor spreads, first into the wall of the gut and then beyond, determines the severity and stage of the cancer.

Need to identify more specific risk factors

One way to tackle the rising trend in young-onset colorectal cancer is earlier diagnosis. For that, there is a need to identify those at higher risk of early-onset disease.

However, so far, few studies have identified risk factors that are specific to those aged 20–49 years.

For their investigation, Dr. Cao and colleagues turned to the Nurses’ Health Study, which is part of a project that started in 1976 and is looking into “risk factors for major chronic diseases in women.”

Read on: The value of the virtual clinic in digital diagnosis

The team analyzed data on 89,278 women in the Nurses’ Health Study II. This data included surveys about cancer diagnoses and sedentary behavior, including the amount of time that the women spent sitting and watching TV.

During a 22-year follow-up period, 118 of the women received a diagnosis of young-onset colorectal cancer.

The researchers then carried out an analysis that compared the women who developed cancer with those who did not, focusing on the time that they spent sitting and viewing TV.

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