New research published in the journal PLOS Medicine has explored the relationship between sedentary behaviour and the incidence and mortality rates of cancer. The study indicates that the duration of uninterrupted sitting time may be a significant factor in an individual's cancer risk, rather than overall sedentary time that is broken up by periods of activity.
However, experts are urging caution in interpreting the findings, highlighting the complexities involved in establishing clear causal links. Professor Kevin McConway, Emeritus Professor of Applied Statistics at the Open University, noted the intricate nature of the study's conclusions. He suggested that while the findings are interesting, they are challenging to interpret definitively, particularly concerning the distinction between prolonged and interrupted sedentary periods.
Professor McConway raised concerns about some of the researchers' conclusions, arguing they may not be as clear-cut as presented. He pointed out that previous research has already indicated a higher cancer risk for individuals with more sedentary lifestyles, such as those who spend extended periods watching television. The new study aims to refine this understanding by focusing on whether the sedentary time occurs in long, unbroken sessions or is more frequently interrupted by physical activity.
The study employed two sets of statistical analyses. The first aimed to model sedentary behaviour that was interrupted by other activities, while the second, known as isotemporal substitution models, theoretically estimated the effect of replacing one type of sedentary behaviour with another or with physical activity. Professor McConway expressed doubts about the interpretability of the first set of models and suggested that the results from the second set of analyses could lead to different conclusions regarding the importance of breaking up sedentary activity.
Adding to this perspective, Professor Stephen Burgess, a Statistician at the MRC Biostatistics Unit, University of Cambridge, emphasised that the study is a statistical analysis of an observational study, meaning it indicates correlation rather than direct causation. He stated that while the authors made commendable efforts to account for other factors, it is impossible to be certain that all relevant variables have been addressed. Professor Burgess suggested that observed correlations might reflect underlying social factors, such as job type and income, rather than solely attributable to sedentary behaviour itself.