Mortality risk and perceived quality of life as a function of waking time in discretionary movement-based behaviors: isotemporal substitution effects.

OBJECTIVE: Previous research has examined associations of sedentary behavior (SB), light-intensity physical activity (LIPA) and moderate-to-vigorous physical activity (MVPA) with health-related quality of life (HRQOL) and mortality. However, most of these studies have been limited to examining their potential "independent" effects, as opposed to whether mortality risk and HRQOL vary as a function of waking time in these discretionary movement-related behaviors, which was this study's purpose.

METHODS: Data from the 2003-2006 NHANES were employed, with follow-up mortality assessed through 2011 (5377 adults 20-85 years). HRQOL was assessed via survey, with physical activity assessed using an accelerometer over a 7-day monitoring period. Isotemporal substitution analyses were employed.

RESULTS: Participants engaged in little MVPA during their monitored waking time and higher mortality risk appeared to cluster more so among those spending a greater proportion of their day in SB with less LIPA engagement. Substituting 30 min/day of SB with MVPA would be expected to reduce mortality risk by 81 % (HRadjusted  = 0.19; 95 % CI: 0.06-0.60; P = 0.006) and reduce worse HRQOL by 72 % (OR = 0.28; 95 % CI: 0.13-0.58; P = 0.001).

CONCLUSIONS: Allocation of waking time in movement-based behaviors is associated with all-cause mortality and HRQOL. Thus, clinicians should encourage their patients to substitute SB with reasonable amounts of LIPA and MVPA.