TIME Cancer

Sitting Can Increase Your Risk of Cancer By Up to 66%

For a change, the cancer-promoter isn't something you eat or breathe, but something you do every day

By now we’re pretty familiar with the biggest cancer-triggers in our lives – processed meats, smoking, and tumor-causing pollutants in the air, to name a few. But it turns out there’s another hidden cancer contributor that occupies much of our daily lives: sitting.

In a study published in the Journal of the National Cancer Institute, researchers report that people who spend more hours of the day sitting have up to a 66% higher risk of developing certain types of cancer than those who aren’t as sedentary.

MORE: Get Up! Sitting Less Can Add Years to Your Life

These results go beyond the advice by most health professionals for everyone to become more physically active. In reviewing 43 studies in which volunteers were asked about their daily activities and their cancer incidence, the investigators found that the link between sitting and cancer remained strong no matter how physically active the participants were. In other words, even people who worked out regularly but who spent more hours on the couch watching TV, for instance, showed higher rates of cancer than those who didn’t sit as much.

Sedentary behavior was associated with a 24% greater risk of developing colon cancer, a 32% higher risk of endometrial cancer, and a 21% increased risk of lung cancer. When the researchers delved deeper into different types of sedentary habits, they found that watching TV was linked to a 54% higher risk of colon cancer and a 66% greater risk of endometrial cancer. For every additional two hours that participants spent sitting during the day, their risk of colon cancer rose by 8%, and their risk of endometrial cancer went up by 10%. They didn’t find a link between sedentary behavior and other types of cancer, including breast, prostate, and non-Hodgkin lymphoma.

The findings, says Dr. Graham Colditz, of Washington University School of Medicine, who wrote an editorial accompanying the study, highlight the difference between being physically active and being sedentary. It’s not enough to just be active—it’s also important to sit less. But most public health messages aren’t stressing the distinction. “People are not talking about sitting time in the same way as physical activity,” he says. “Guidelines say limit the time spent sitting without drilling into how long or what types of sitting they are talking about.”

MORE: Now There’s Another Reason Sitting Will Kill You

The difference is important, especially since the latest research suggests that sitting too much may have its own, independent harms on our health. A recent study, for example, found that people who got up and did light to moderate walking after lunch had lower blood sugar levels and less of a peak in blood sugar than people who didn’t get up after eating.

Part of sitting’s adverse effects, especially on endometrial cancer, which is strongly tied to obesity, may be through weight gain. Obesity can promote cancer-causing processes such as inflammation and may enhance certain hormones that are linked to tumor formation. Weight gain can also lead to lower levels of vitamin D, and that can contribute to higher risk of colon cancer.

The authors also point out that TV viewing in particular may be associated with higher rates of certain cancers since TV watchers tend to drink more sugared sodas and unhealthy, processed snack foods that can both contribute to obesity and increase exposure to potential food-based cancer-causing agents.

MORE: Watching TV: Even Worse for Kids Than You Think

Cutting back on sitting time may not be easy, however, since most office workers tend to sit at a desk in front of computers. But Colditz says there are ways to be less sedentary, either at home or at the office. Try to take breaks every couple of hours, to take a quick walk around the halls or to step outside (bathroom breaks don’t count). And not eating lunch at your desk can also be a way to schedule a physical break in your day. What you don’t want to do, he says, is to make a habit of sitting (in a car or bus or train) to work, sitting at your desk for most of the day, eating lunch at your desk (again, while sitting), and then finally getting up to go home, where you may spend several more hours sitting in front of a TV.

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