Mortality Risk Reductions for Replacing Sedentary Time With Physical Activities

Introduction: Excess sitting is a risk factor for early mortality. This may be resulting, at least in part, from the displacement of physical activity with sedentary behaviors. The purpose of this observational study was to examine the mortality risk reductions associated with replacing 30 minutes/day sitting for an equivalent duration of light or moderate to vigorous physical activity (MVPA). Methods: Participants included 37,924 men and 54,617 women in the Cancer Prevention Study-II Nutrition Cohort, of which 14,415 men and 13,358 women died during follow-up (1999-2014). An isotemporal substitution approach to the Cox proportional hazards regression model was used to estimate adjusted hazard ratios and 95% CIs for mortality associated with the substitution of 30 minutes/day self-reported sitting for light physical activity or MVPA. Analyses were conducted in 2018. Results: Among the least active participants (<= 17 minutes/day MVPA), the replacement of 30 minutes/day sitting with light physical activity was associated with a 14% mortality risk reduction (hazard ratio=0.86, 95% CI=0.81, 0.89) and replacement with MVPA was associated with a 45% mortality risk reduction (hazard ratio=0.55, 95% CI=0.47, 0.62). Similar associations were seen among moderately active participants (light physical activity replacement, hazard ratio=0.94, 95% CI=0.91, 0.97; MVPA replacement, hazard ratio=0.83, 95% CI=0.76, 0.88). However, for the most active (MVPA >38 minutes/day), substitution of sitting time with light physical activity or MVPA was not associated with a reduction in mortality risk (hazard ratio=1.00, 95% CI=0.97, 1.03, and hazard ratio=0.99, 95% CI=0.95, 1.02, respectively). Conclusions: These findings suggest that the replacement of modest amounts of sitting time with even light physical activity may have the potential to reduce the risk of premature death among less active adults. (C) 2019 American Journal of Preventive Medicine. Published by Elsevier Inc. All rights reserved.