Each additional hour spent in prolonged, uninterrupted sedentary behaviour is associated with a 9% higher risk of dying from cancer, according to a new study published on July 2 in the journal PLOS Medicine. Led by Frederick Ho at the University of Glasgow, the research suggests that not only the amount of time people spend sitting but also how that time is accumulated may influence long-term health. While previous studies have linked sedentary lifestyles to poorer health outcomes, most public health recommendations have focused on reducing total sitting time rather than encouraging people to break up long periods of inactivity.
To investigate the health effects of sedentary behaviour patterns, the researchers analysed data from 91,292 participants in the UK Biobank. Participants wore wrist-based activity monitors continuously for seven days, allowing researchers to measure their movement objectively. They were then followed for a median of 12.38 years. The team classified activity into prolonged sedentary behaviour, defined as sitting or remaining inactive for at least 30 minutes with at least 90% of the time spent sedentary, interrupted sedentary behaviour, and varying levels of physical activity.
The findings showed that prolonged sedentary behaviour was consistently associated with poorer health outcomes. Each additional hour spent in uninterrupted sedentary activity was linked to a 9% increase in cancer mortality risk. It was also associated with a greater likelihood of developing cancer overall, including obesity-related cancers such as cancers of the oesophagus, liver, kidney, pancreas, colorectum, breast, ovary, and thyroid, as well as cancers associated with type 2 diabetes. In contrast, sedentary time that was regularly interrupted by movement was associated with lower risks across these health outcomes, highlighting the potential importance of taking frequent activity breaks throughout the day.
The researchers also examined whether replacing prolonged sedentary time with physical activity could reduce health risks. Their analysis indicated that substituting just one hour per day of uninterrupted sitting with light physical activity was associated with a 12% lower risk of cancer death. The findings suggest that even modest increases in movement, such as standing, walking, or completing light household tasks, may offer measurable health benefits. This supports growing evidence that small changes in daily behaviour can complement regular exercise in reducing disease risk.
The authors caution that the study has important limitations. Because it is based on a single cohort of volunteers from the UK Biobank, who tend to be healthier and more physically active than the general population, the results may not apply equally to everyone. As an observational study, it cannot establish that prolonged sitting directly causes cancer or cancer-related deaths. In addition, the researchers were unable to determine the context of sedentary behaviour, such as whether participants were sitting at work, travelling, or relaxing at home, factors that could influence health outcomes.
According to the researchers, the results suggest that the health effects of sedentary behaviour depend not only on the total amount of time spent sitting but also on whether that time is broken up by movement. Experimental studies have already shown that interrupting prolonged sitting with brief periods of activity can improve metabolic function compared with remaining seated continuously. The team argues that current health guidelines place considerable emphasis on moderate- and vigorous-intensity exercise. Still, light movement throughout the day should also be recognised as an important component of disease prevention. They add that future clinical trials will help determine the most effective and personalised strategies for reducing the health risks associated with prolonged sitting.
More information: Ziyi Zhou et al, Accelerometry-measured prolonged and interrupted sedentary behavior and cancer incidence and mortality: A cohort study of 91,292 UK Biobank participants, PLOS Medicine. DOI: 10.1371/journal.pmed.1004767
Journal information: PLOS Medicine Provided by PLOS
