Prolonged Sitting Associated With Higher Cancer Mortality Risk in UK Biobank Study

Long, uninterrupted periods of sedentary behavior were associated with a higher risk of cancer death in a cohort study of 91,292 UK Biobank participants. The researchers also found that breaking up sedentary time with movement was associated with lower risks across the outcomes examined.

The study, led by Frederick Ho of the University of Glasgow and published in PLOS Medicine, used activity-monitor data collected over seven days for each participant. Researchers then followed the group for a median of 12.38 years.

Prolonged sedentary behavior was defined as periods lasting at least 30 minutes during which at least 90% of the time was spent sedentary. The researchers classified shorter periods, or periods containing more than 10% non-sedentary activity, as interrupted sedentary behavior. Sedentary behavior included sitting, reclining or lying down while awake.

Each additional daily hour of prolonged sedentary behavior was associated with a 9% higher risk of cancer mortality. Longer periods were also associated with higher risks of overall cancer incidence and cancers related to obesity and type 2 diabetes, including esophageal, liver, kidney, pancreatic, colorectal, breast, ovarian and thyroid cancers.

Interrupted sedentary behavior showed the opposite pattern, with lower risk across all the outcomes studied. The researchers estimated that replacing one hour of prolonged sedentary behavior each day with light physical activity was associated with a 12% lower risk of cancer death.

Those figures describe statistical associations, not proof that prolonged sitting caused cancer or cancer mortality. Because the research was observational, it cannot establish causation. The study also did not record why participants were sedentary, such as whether they were sitting for work or driving.

The findings came from a single group of UK Biobank volunteers. The source notes that UK Biobank participants tend to be more physically active than the general UK population and may reflect health volunteer bias, limiting how broadly the results apply.

The authors said the health relationship with sedentary behavior may depend not only on the total amount of time spent inactive, but also on whether that time accumulates in long bouts or is interrupted by activity. They pointed to experimental research showing that short activity breaks can improve metabolic responses compared with uninterrupted sitting, while also noting that clinical trials would be needed to develop more tailored strategies.

The study was supported by the American Cancer Society and the U.S. National Institutes of Health. The researchers reported that the funders had no role in the study’s design, data collection and analysis, publication decision or manuscript preparation.