Each extra hour of prolonged sitting linked to 9% higher cancer death risk

The research was led by Frederick Ho of the University of Glasgow, UK, and colleagues, and was published in the open access journal PLOS Medicine.

Why Sitting Patterns May Matter

Earlier research has linked greater amounts of sedentary behavior, including sitting, reclining, or lying down while awake, with poorer health outcomes. Most current guidance, however, concentrates on the total amount of time people spend sedentary.

The new findings suggest that the pattern of that sedentary time may also be important. Sitting for many shorter periods may not carry the same associations as remaining sedentary for longer, uninterrupted stretches.

Tracking More Than 91,000 Adults

Researchers examined data from 91,292 participants in the UK Biobank. Each participant wore an activity monitor for 7 days, and researchers then followed the group for a median of 12.38 years.

The researchers divided activity into several categories. Prolonged sedentary behavior was defined as bouts lasting at least 30 minutes with at least 90% of that period spent sedentary. Interrupted sedentary behavior included periods lasting less than 30 minutes or periods in which more than 10% of the time involved non-sedentary activity. Different levels of physical activity were also measured.

Longer Sitting Linked to Higher Cancer Risk

Greater amounts of prolonged sedentary behavior were associated with a higher risk of cancer mortality (HR 1.09; 95% CI 1.06, 1.11), overall cancer incidence, obesity-related cancers (such as esophageal, liver, kidney, pancreatic, colorectal, breast, ovarian, and thyroid cancers), and type 2 diabetes-related cancers.

Interrupted sedentary behavior was associated with the opposite pattern, showing lower risk across all of the outcomes examined.

The researchers also estimated what might happen if prolonged sitting were replaced with movement. Substituting one hour per day of prolonged sedentary behavior with light physical activity was associated with a 12% lower risk of cancer death (HR 0.88; 95% CI 0.79, 0.99).

Important Study Limitations

The findings come from a single cohort of UK Biobank volunteers. This group is known to have health volunteer bias and tends to be more physically active than the general UK population, which means the results may not apply equally to everyone.

The observational study also cannot establish that prolonged sitting directly causes cancer or cancer death. In addition, researchers did not have information about the circumstances in which participants were sedentary, such as whether they were sitting while working or driving.

"Our findings suggest that the health effects of sedentary behavior may depend not only on total sedentary time, but also on whether that time is accumulated in prolonged bouts or interrupted by activity," the authors say. "This pattern is biologically plausible: experimental studies have shown that interrupting prolonged sitting with short bouts of activity can improve metabolic responses compared with uninterrupted sitting."

Light Movement Could Still Matter

The results point to a potentially important role for everyday movement, even when it does not qualify as moderate or vigorous exercise.

The authors add, "Current health guidelines focus heavily on moderate or vigorous exercise, but our findings show that light movement shouldn't be ignored. Moving forward, clinical trials will help us move beyond blanket advice and develop personalized strategies for breaking up sitting time."

Funding: This work was supported by the American Cancer Society (grant code MRSG-17-200-01-NEC to MS, www.cancer.org), and the U.S. National Institutes of Health (grant code U01CA261961, R01CA263776, and R01CA285851 to MS, www.nih.gov). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.