TV Watching Associated with 70% Increase in Colorectal Cancer Risk

An Arivale Hot Topic

Jennifer Lovejoy, Arivale Chief Science Officer, PhD
Jennifer Lovejoy
Arivale Chief Science Officer, PhD

A new study of tens of thousands of women under the age of 50 revealed a dramatic increase in colorectal cancer risk associated with watching multiple hours of television per day.

But before we get to that, let’s jump back for a minute. Health authorities around the world are concerned about a dramatic increase in colorectal cancer rates among people as young as 20 – despite the overall incidence of colorectal cancer decreasing.

Worryingly, young-onset colorectal cancer tends to be more aggressive – and come with greater loss of life – than cases diagnosed after the age of 50. In fact, concerns about the trend in younger ages at diagnosis recently prompted the American Cancer Society to recommend colon cancer screenings begin at age 45, rather than 50.

The Study

As reported by NBC News, the new study found watching more than one hour of TV per day was associated with a 12 percent increased risk in colorectal cancer and watching more than two hours per day was associated with a 70 percent increased risk.

The study was based on the Nurses’ Health Study, a large, longitudinal population study that began in 1989 when over 116,000 female nurses were enrolled and had baseline data collected on a variety of health risk factors. Follow-up data has been collected on this cohort every two years since.

The researchers documented 118 cases of young-onset colorectal cancer in this population over 22 years of follow up, with an average age at diagnosis of 45. They looked at a variety of sedentary behaviors, including TV watching, working at a desk, reading, and sitting at meals. But, only TV watching was significantly associated with young-onset colorectal cancer.

Importantly, the association between TV watching and colorectal cancer risk remained after statistically adjusting for other known risk factors, such as smoking, high BMI, low physical activity, and poor diet.

Arivale’s Take

This study is consistent with previous findings showing a sedentary lifestyle is associated with late-onset colorectal cancer in older adults. While the mechanism for the association between TV watching and young-onset colorectal cancer is unclear, the study’s authors note that being sedentary has previously been associated with increased blood sugar levels, lower vitamin D levels, and abnormal gut microbiome patterns, all of which are risk factors for colorectal cancer.

One limitation of the study is that the group who watched the most television also engaged in other unhealthy behaviors: they smoked more cigarettes, ate a less healthy diet, were less likely to take multivitamins, and had higher rates of diabetes. Although the researchers statistically controlled for these confounders, it’s still possible that TV watching is simply a “marker” for some other lifestyle factor that is the actual cause of the increased colorectal cancer risk.

Another limitation is that the group was all female and primarily white, although the researchers note this is the population most impacted by young-onset colorectal cancer.

It’s now well established that sedentary behavior – extended TV watching in particular – is associated with chronic diseases, including type 2 diabetes, cardiovascular disease, and cancer.  This is an independent risk, meaning it’s not lessened no matter how much exercise you do.

The lifestyle solution is to make sure you take frequent standing breaks during any sedentary behavior, especially TV watching. Make a habit that, whenever a commercial comes on, you stand until your program resumes. If you’re streaming shows or movies without commercials, set an alarm on your watch or phone to stand up at least every 30 minutes and march in place for a couple minutes to get some blood flowing.

Standing and performing light activity both increase blood flow and muscle contraction, which may help lower the risk of colorectal cancer, and the study did observe a trend toward reduced risk of young-onset colorectal cancer in participants who reported more light-intensity behaviors, such as standing or walking at work or home.

Lastly, be sure to talk to your doctor about the appropriate age for you to begin screening for colorectal cancer, especially if the disease runs in your family.

Further Reading



[Arivale Hot Topics address health stories currently in the news. The Arivale Clinical Team’s commentary on these news articles is not a review of the scientific evidence, nor an endorsement of a specific study, and is not meant as official medical opinion.]