Sitting for long, unbroken stretches every day is linked to a measurably higher risk of dying from cancer, according to a large study published on 2 July in the journal PLOS Medicine.
The research, led by Frederick Ho of the University of Glasgow and colleagues, found that each additional hour of prolonged, uninterrupted sedentary behaviour in a person's day is associated with a 9% higher risk of cancer death.
The findings are based on data from 91,292 participants in the UK Biobank, all of whom wore activity monitors for seven days. Researchers then tracked their health outcomes over a median follow-up period of 12.38 years.
What counts as prolonged sitting
The study drew a distinction that most existing health guidelines do not. Rather than looking only at total time spent sedentary, researchers separated behaviour into two categories: prolonged sedentary bouts, defined as periods of at least 30 minutes where at least 90% of the time was spent sedentary, and interrupted sedentary behaviour, which involved shorter or broken-up periods of inactivity.
The difference turned out to matter significantly.
Prolonged sedentary behaviour was associated with higher risks of overall cancer incidence, cancer mortality, obesity-related cancers such as liver, kidney, pancreatic, colorectal, breast, and thyroid cancers, and cancers linked to type 2 diabetes.
Interrupted sedentary behaviour showed the opposite pattern and was associated with lower risk across all the same outcomes.
What movement does
Replacing one hour of prolonged sitting with light physical activity each day was associated with a 12% lower risk of cancer death.
The researchers noted that this is biologically plausible. Experimental studies have previously shown that breaking up long sitting periods with short bouts of movement can improve metabolic responses compared with sitting without interruption.
The authors said current health guidelines place heavy emphasis on moderate or vigorous exercise but underestimate the value of lighter movement through the day.
"Moving forward, clinical trials will help us move beyond blanket advice and develop personalised strategies for breaking up sitting time," they wrote.
Limitations
The study is observational and based on a single cohort. UK Biobank volunteers are known to be more physically active than the general UK population, which means the findings may not apply universally. The researchers also had no data on the context of sedentary behaviour, such as whether participants were sitting at a desk, driving, or watching television.
The study does not establish causation and the authors acknowledge this directly.
The research was supported by the American Cancer Society and the US National Institutes of Health. The full paper is available in PLOS Medicine at https://plos.io/4oi0sJO .
