Study Finds Cancer Risk Increases as Physical Activity Decreases

Graham A. Colditz, MD, DrPH

Spending all day sitting on the couch to binge watch your favorite television show not only isn’t great for your waistline, recent research suggests it could increase your risk for cancer.

A study published in the July 2014 issue of the Journal of the National Cancer Institute examined 68,936 cancer patients through 43 existing studies to analyze the link between sedentary behavior and the risk of cancer. The study finds the risk of developing colon cancer, endometrial cancer, and lung cancer rises with increased TV viewing time, occupational sitting time, and total sitting time.

The researchers hypothesize that TV viewing time has a strong relationship with colon and endometrial cancer due to its association with consumption of junk food and beverages high in sugar.

“That sedentariness has a detrimental impact on cancer even among physically active persons implies that limiting the time spent sedentary may play an important role in preventing cancer,” the study authors wrote.

Higher overall sedentary behavior was not found to increase risk of cancer of the breast, rectum, ovaries, prostate, stomach, esophagus, testes, renal cell, and non-Hodgkin lymphoma. With each 2-hour increase in sitting time per day, the risk for colon cancer rises by 8%, endometrial cancer by 10%, and lung cancer by 6%.

Sitting time increases were not found to increase the risk for cancer of the breast, ovary, prostate, or non-Hodgkin lymphoma. Even people who are otherwise considered physically active but who still spend a significantly large amount of time sitting during the day are at an increased risk for cancer.

Sedentary time accumulated at school or work, while driving or using mass transportation, watching TV, and playing video games was also related to increased obesity and diabetes risk, cardiovascular disease, and all-cause mortality.

“Technologies equip the modern society and shift the dynamic of household work, transportation, and communication and the nature of occupations; thus our daily life demands less physical activity and induces more sitting,” wrote Lin Yang and Graham A. Colditz, MD, DrPH, in an accompanying commentary on the study.

While time spent on the couch watching TV can easily be reduced through the adoption of an active lifestyle, sedentary behavior in the workplace is harder to avoid. As a result, Yang and Colditz suggest adopting new occupational policies that encourage employees to spend less time at their desks staring at a computer screen.

“Reductions in sedentary behavior are recommended for cancer reduction and improvement in overall mortality,” Yang and Colditz wrote. “Strategies remain poorly defined to meet this goal independent of weight control. Priority should be placed on refining interventions, independent of physical activity and obesity prevention, to reduce sedentary time and lower cancer risk and overall mortality.”