Association of Sedentary Behavior With Cancer Mortality in Middle-aged and Older US Adults.
Level 3 - non-randomized controlled study
Prospective cohort study
PubMed 32556069 · doi:10.1001/jamaoncol.2020.2045
What was done
A prospective cohort analysis of 8,002 Black and White adults aged 45 years or older from the REGARDS study in the contiguous US. Participants wore a hip-mounted accelerometer for 7 consecutive days to measure total sedentary time, sedentary bout duration, light-intensity physical activity (LIPA), and moderate- to vigorous-intensity physical activity (MVPA). The primary outcome was cancer mortality over a mean follow-up of 5.3 years. Multivariable models adjusted for MVPA, and isotemporal substitution was modeled for replacing 30 minutes of sedentary time with activity.
What was found
Over a mean (SD) follow-up of 5.3 (1.5) years, 268 participants (3.3%) died of cancer. Total sedentary time was significantly associated with cancer mortality after multivariable adjustment including MVPA: tertile 2 vs tertile 1 hazard ratio (HR) was 1.45 (95% CI, 1.00-2.11), and tertile 3 vs tertile 1 HR was 1.52 (95% CI, 1.01-2.27). Longer sedentary bout duration was not significantly associated with cancer mortality after MVPA adjustment (tertile 2 HR, 1.26; 95% CI, 0.90-1.78; tertile 3 HR, 1.36; 95% CI, 0.96-1.93). Replacing 30 minutes of sedentary time with LIPA was associated with an 8% lower risk of cancer mortality (HR, 0.92; 95% CI, 0.86-0.97), and replacement with MVPA was associated with a 31% lower risk (HR, 0.69; 95% CI, 0.48-0.97).
Why it matters
This study provides objective accelerometer data showing that higher total sedentary volume independently increases cancer mortality risk, while reallocating sedentary time to light or moderate-to-vigorous activity reduces this risk.
Limits
Physical activity and sedentary behavior were measured during a single 7-day period at baseline, which may not capture changes over time. The observational design cannot establish causality and remains vulnerable to unmeasured confounding or reverse causation. The follow-up was relatively short (5.3 years) with a low number of total cancer deaths (n = 268), and site-specific cancer deaths were not reported.
Cited by
- supports Sedentary time is an independent risk factor for higher all-cause mortality and increased cancer risk.