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A new study suggests that how long people sit without getting up may matter for cancer risk, with prolonged, uninterrupted sedentary periods linked to a higher risk of dying from cancer.
Researchers led by Frederick Ho of the University of Glasgow in the UK found that each additional hour of prolonged sedentary behavior was associated with a 9% higher risk of cancer mortality. The findings were published in the open-access journal PLOS Medicine.
The study analyzed data from 91,292 UK Biobank participants, who wore activity monitors for seven days and were then followed for a median of 12.38 years.
Researchers defined prolonged sedentary behavior as periods lasting at least 30 minutes during which at least 90% of the time was spent sedentary. They compared these periods with shorter or interrupted periods of sitting and also assessed participants’ levels of physical activity.
The findings showed that greater amounts of prolonged sedentary behavior were associated with higher risks of cancer death, overall cancer incidence, obesity-related cancers and type 2 diabetes-related cancers.
By contrast, interrupted sedentary behavior was associated with lower risks across the outcomes studied.
The researchers also estimated the potential benefits of replacing prolonged sitting with physical activity. Replacing one hour of prolonged sedentary behavior each day with light physical activity was associated with a 12% lower risk of dying from cancer.
The researchers cautioned that the study does not prove prolonged sitting directly causes cancer. The analysis was observational and based on UK Biobank volunteers, who tend to be healthier and more physically active than the general UK population.
The study also did not record what participants were doing while sedentary, such as working at a desk, watching television or driving.
The researchers said the findings indicate that health risks may depend not only on the total amount of sedentary time but also on whether that time is accumulated in long, uninterrupted periods.
They suggested that short bouts of light movement could be important, even for people who do not regularly engage in moderate or vigorous exercise.
The authors said future clinical trials could help develop more personalized strategies for breaking up prolonged sitting and determining how much movement is needed to reduce associated health risks.