Background
Sedentary behavior accounts for a majority of waking time for children and adults. Multiple studies have shown that excessive sedentary behavior, such as daily prolonged sitting, increases the risk of cardiovascular disease, type 2 diabetes, obesity, certain cancers, and all-cause mortality. The adverse effects are most prominent in people with low levels of physical activity.
Study Details
Dr. Frederick Ho from the University of Glasgow and colleagues published a prospective cohort study in PLoS Medicine, analyzing data from 91,292 participants in the UK Biobank. The average age was 56, and 56% were women. All participants wore an accelerometer for one week to objectively measure physical activity.
Prolonged sedentary behavior was defined as an episode of at least 30 minutes where at least 90% of the time was sedentary. Physical activity was classified as low (slow walking), moderate (moderate walking), and vigorous (fast walking and high-energy activities).
Key Findings
- During follow-up, 12,392 participants developed cancer, and 1,726 died from cancer.
- Each additional hour of prolonged sedentary behavior per day was associated with a 10% higher hazard of cancer mortality (HR 1.10).
- Replacing one hour of sedentary time with low-level physical activity reduced cancer mortality risk by 12%.
- Replacing with 30 minutes of moderate activity reduced risk by 8%.
- Adding 5 minutes of vigorous activity daily reduced risk by 22%.
- Similar associations were observed for lung, breast, oral cancers, leukemia, and non-Hodgkin's lymphoma.
Expert Commentary
Rachel Richardson from Cochrane in York, England, noted that the main strength is the use of accelerometers for objective measurement rather than self-reporting. However, she cautioned that the study population is not representative of the general UK population (older and more health-conscious), and the follow-up period was short. As an observational study, it cannot rule out all confounding factors.
Practical Advice
Researchers suggest that reducing long, uninterrupted periods of sedentary behavior and replacing them with physical activity—even of light intensity—may be a practical target for reducing cancer risk. For example, stand up and move for a few minutes every 30 minutes, or choose walking over short car trips.