Joint effects of objectively-measured sedentary time and physical activity on all-cause mortality

Objective. Examine the joint effects of objectively-measured sedentary time and moderate-to-vigorous physical activity (MVPA) on all-cause mortality. Methods. The present study included data from the 2003-2006 National Health & Nutrition Examination Survey, with mortality follow-up data (via National Death Index) through 2011 (N = 5575 U.S. adults). Sedentary time (activity counts/min between 0 and 99) and MVPA (activity counts/min = 2020) were objectively measured using the ActiGraph 7164 accelerometer. Results. The median age of the participants was 50 yrs; proportion of men was 50.2%; proportion of whites was 53.8%, 18.7% for blacks; median follow-up was 81 months; and 511 deaths occurred over the follow-up period. After adjusting for age, gender, race-ethnicity, cotinine, weight status, poverty level, C-reactive protein and comorbid illness (summed score of 0-8 chronic diseases), and for a 1 min increase in MVPA and sedentary time, both MVPA (HRadjusted = 0.98; 95% CI: 0.96-0.99; P = 0.04) and sedentary time (HRadjusted = 1.001; 95% CI: 1.0003-1.002; P= 0.008)were independently associated with all-cause mortality. Further, MVPA was associated with all-cause mortality among those with greater (above median) sedentary time (HRadjusted = 0.95; 95% CI: 0.93-0.97; P < .001). Sedentary time was not associated with all-cause mortality among those engaging in above median levels of MVPA (HRadjusted = 0.998; 95% CI: 0.996-1.001; P = .32), but sedentary time was associated with increased mortality risk among those below median levels of MVPA (HR = 1.002; 95% CI: 1.001-1.003; P < 0.001). Conclusions. Sedentary time and MVPA are independently associated with all-cause mortality. Above median sedentary time levels did not negate the beneficial effects of MVPA on all-cause mortality risk. (C) 2016 Elsevier Inc. All rights reserved.