Prolonged sedentary behavior associated with increased cancer risk, study finds
Each additional hour of prolonged, uninterrupted sedentary behavior in a person's day is associated with a 9% higher risk of cancer death, according to a study published July 2nd in the open access journal PLOS Medicine by Frederick Ho of the University of Glasgow, UK, and colleagues.
Previous studies have shown that spending more total time on sedentary behavior, such as sitting, reclining or lying down while awake, is linked to poorer health outcomes. However, most sedentary behavior guidelines focus on total time spent sedentary, rather than whether that time is accumulated in many short intervals or fewer prolonged intervals.
In the new study, researchers analyzed data from 91,292 UK Biobank participants who had worn activity monitors for 7 days and were followed for a median of 12.38 years afterward. Activity was categorized as either prolonged sedentary (bouts of at least 30 minutes with at least 90% of time sedentary), interrupted sedentary behavior (which lasted less than 30 minutes or was broken up with more than 10% non-sedentary time), or varying degrees of physical activity.
Prolonged sedentary behavior was 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 showed the opposite pattern, associated with lower risk across all outcomes. Replacing 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).
As a single-cohort study of UK Biobank volunteers, who have known health volunteer bias and higher physical activity levels than the general UK population, the findings may not be generalizable and do not prove causality. The researchers also had no data on the context of sedentary behavior, such as whether it was during work 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.”
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 personalised strategies for breaking up sitting time.”
Reference:
Ziyi Zhou,Stewart G. Trost,Gemma C. Ryde,Solange Parra-Soto,Zhe Fang,Chao Xu, Accelerometry-measured prolonged and interrupted sedentary behavior and cancer incidence and mortality: A cohort study of 91,292 UK Biobank participants, PLOS Medicine, https://doi.org/10.1371/journal.pmed.1004767
