Mortality Risk Reductions for Replacing Sedentary Time with Physical Activities

Abstract

BACKGROUND: Insufficient physical activity is a well-established risk factor for chronic disease and early mortality. More recent evidence suggests that excess sitting time may be an additional risk factor, independent of physical inactivity. This may be due, at least in part, to the displacement of physical activities with sedentary behaviors. PURPOSE: To examine the mortality risk reductions associated with replacing thirty minutes of daily sitting time for an equivalent duration of physical activity. METHODS: Participants included 40,866 men and 60,891 women in the Cancer Prevention Study-II Nutrition Cohort. An isotemporal substitution approach to Cox proportional hazards regression models were used to estimate adjusted hazard ratios (HR) and 95% confidence intervals (HR, 95% CI) for all-cause mortality associated with the substitution of thirty minutes of daily sitting time with an equal duration of light or moderate-to-vigorous intensity physical activity (LPA, MVPA). RESULTS: During 14 years (1999-2013) of follow-up, 16,163 men and 15,638 women died. Overall, reallocation of 30 min[BULLET OPERATOR]day-1 of sitting to LPA (HR=0.94, 0.92-0.97) or MVPA (HR=0.91, 0.88-0.93) was associated with significant reductions in mortality risk. Among the least active participants, the replacement of 30 min[BULLET OPERATOR]day-1 of sitting time with 30 min[BULLET OPERATOR]day-1 LPA was associated with a 14% mortality risk reduction (HR=0.86, 0.83-0.89) and replacement with MVPA was associated with a 50% mortality risk reduction (HR=0.50, 0.44-0.58). Similar associations were seen among the moderately active group (HR=0.91, 0.89-0.96 for LPA replacement, HR=0.65, 0.56-0.79 for MVPA replacement). However, among the most active participants, substitution of sitting time with LPA or MVPA was not associated with a significant reduction in mortality risk (HR=1.00, 0.97-1.02, HR=0.97, 0.95-1.01, respectively). CONCLUSIONS: Among the least active and moderately active, the replacement of modest amounts of sitting time with either LPA or MVPA was associated with longevity, although the associations were strongest when sitting time was replaced with MVPA.