Among 91,292 UK Biobank participants, spending more time in prolonged sedentary bouts was linked to greater risks of developing and dying from cancer, whereas sedentary time accumulated in shorter, interrupted bouts was linked to lower cancer risk.
Researchers conducted a prospective cohort study to examine whether prolonged and interrupted sedentary behavior were independently associated with cancer risk. The analysis included participants without a history of cancer who had valid wrist-worn accelerometer data collected between 2013 and 2015. Participants were followed for a median of 12.4 years using linked hospital admission and mortality records. Outcomes included overall cancer mortality and the incidence of overall cancer, obesity-related cancers, type 2 diabetes-related cancers, and 23 site-specific cancers.
Sedentary behavior and physical activity were measured using a wrist-worn triaxial accelerometer worn continuously for 7 days. A validated two-step random forest machine-learning algorithm classified activity into sedentary behavior and light-, moderate-, and vigorous-intensity physical activity. Researchers defined prolonged sedentary behavior as sedentary bouts lasting at least 30 minutes in which at least 90% of the time was sedentary. Sedentary bouts that did not meet those criteria were classified as interrupted sedentary behavior. Multivariable Cox proportional hazards models adjusted for demographic, socioeconomic, dietary, lifestyle, and health-related factors. Sensitivity analyses additionally adjusted for body mass index and multimorbidity and excluded the first 2 years of follow-up. Researchers also used isotemporal substitution models to estimate associations with replacing prolonged sedentary behavior with interrupted sedentary behavior or physical activity.
During follow-up, 12,392 participants developed cancer and 1,726 died of cancer. Each additional hour per day of prolonged sedentary behavior was associated with a higher risk of cancer mortality, overall cancer incidence, obesity-related cancer, and type 2 diabetes-related cancer. Conversely, each additional hour per day of interrupted sedentary behavior was associated with a lower risk of those outcomes. Similar associations were reported for breast, lung, and oral cancers, non-Hodgkin lymphoma, and leukemia. The associations remained consistent in sensitivity analyses.
In isotemporal substitution analyses, replacing prolonged sedentary behavior with light-, moderate-, or vigorous-intensity physical activity was associated with lower risks across the composite cancer outcomes, with the greatest reductions observed for vigorous-intensity activity. While directly replacing prolonged sedentary behavior with interrupted sedentary behavior did not yield statistically significant risk reductions in this model, the researchers noted that, overall, accumulating sedentary time in shorter, interrupted bouts was independently linked to a lower risk of cancer outcomes.
The researchers noted that the study cannot prove causality. They also identified residual confounding, healthy volunteer bias, and measurement imprecision due to only 7 days of accelerometer wear as methodological limitations. They also noted that the 7-day period may not reflect long-term habitual behavior, and that the accelerometer could not identify the context of sedentary activities, such as work, television viewing, or driving.
“Replacing prolonged sedentary behavior with PA [physical activity] was associated with a lower risk of cancer death,” wrote lead study author Ziyi Zhou of the School of Health and Wellbeing, University of Glasgow in the United Kingdom, Department of Epidemiology, Harvard T.H. Chan School of Public Health in Massachusetts, Clinical and Translational Epidemiology Unit, Massachusetts General Hospital and Harvard Medical School in Massachusetts, and colleagues.
The study was funded by the American Cancer Society and the US National Institutes of Health. Frederick K. Ho served as a paid statistical consultant for the PLOS Medicine statistical board. The remaining researchers reported no competing interests.
Source: PLOS Medicine
