Each Extra Hour of Uninterrupted Sitting Linked to 9% Higher Cancer Death Risk

Spending long periods sitting without getting up may carry greater health risks than simply accumulating a high amount of sedentary time over a day, according to a new study led by Frederick Ho of the University of Glasgow, UK, published in the open-access journal PLOS Medicine. The findings suggest the pattern of sedentary time, not only its total amount, may matter for health.

Researchers examined data from 91,292 participants in the UK Biobank, each of whom wore an activity monitor for seven days, and followed the group for a median of 12.38 years. They classified prolonged sedentary behavior as bouts lasting at least 30 minutes with at least 90% of that time spent sedentary, while interrupted sedentary behavior included shorter bouts or periods where more than 10% of the time involved movement.

Greater amounts of prolonged sedentary behavior were associated with a 9% higher risk of cancer death for every additional hour (hazard ratio 1.09), along with higher overall cancer incidence and higher risk of obesity-related cancers such as esophageal, liver, kidney, pancreatic, colorectal, breast, ovarian and thyroid cancer, and of type 2 diabetes-related cancers. Interrupted sedentary behavior showed the opposite pattern, with lower risk across the same outcomes. Replacing one hour per day of prolonged sedentary behavior with light physical activity was associated with a 12% lower risk of cancer death.

The authors note the findings come from a single cohort of UK Biobank volunteers, who tend to be more physically active than the general population, and that as an observational study, it cannot establish that prolonged sitting directly causes cancer death. The researchers also lacked information on the circumstances of participants' sedentary time, such as whether they were sitting at work or while driving.