Abstract
BackgroundSedentary behaviour, sleeping, and physical activity are thought to be independently associated with health outcomes but it is unclear whether these associations are due to the direct physiological effects of each behaviour or because, across a finite 24-hour day, engagement in one behavior requires displacement of another. The aim of this study was to examine the replacement effects of sedentary behaviour (total sitting, television/computer screen time combined), sleeping, standing, walking, and moderate-to-vigorous physical activity on all-cause mortality using isotemporal substitution modelling.MethodsLongitudinal analysis (4.22 ± 0 · 9 years follow-up/849,369 person-years) of 201,129 participants of the 45 and Up study aged ≥45 years from New South Wales, Australia.ResultsSeven thousand four hundred and sixty deaths occurred over follow-up. There were beneficial associations for replacing total sitting time with standing (per-hour HR: 95 % CI: 0.95, 0.94–0.96), walking (0.86, 0.81–0.90), moderate-to-vigorous physical activity (0.88, 0.85–0.90), and sleeping in those sleeping ≤ 7 h/day (0.94, 0.90–0.98). Similar associations were noted for replacing screen time. Replacing one hour of walking or moderate-to-vigorous physical activity with any other activity class was associated with an increased mortality risk by 7–18 %. Excluding deaths in the first 24 months of the follow up and restricting analyses to those who were healthy at baseline did not materially change the above observations.ConclusionAlthough replacing sedentary behaviour with walking and moderate-to-vigorous physical activity are associated with the lowest mortality risk, replacements with equal amounts of standing and sleeping (in low sleepers only) are also linked to substantial mortality risk reductions.Electronic supplementary materialThe online version of this article (doi:10.1186/s12966-015-0280-7) contains supplementary material, which is available to authorized users.
Highlights
Sedentary behaviour, sleeping, and physical activity are thought to be independently associated with health outcomes but it is unclear whether these associations are due to the direct physiological effects of each behaviour or because, across a finite 24-hour day, engagement in one behavior requires displacement of another
There were beneficial associations for replacing sitting with sleeping in those sleeping for ≤7 h/day
The standing time partition models stratified by moderate-to-vigorous physical activity (MVPA) suggested that the beneficial effect of standing on mortality was present in both those who met and did not meet (0.95, 0.94–0.97) the World Health Organization physical activity recommendations. This is the first large-scale epidemiological study examining the replacement effects of sedentary time and other time-dependent behaviours on all-cause mortality using statistical modelling. Both screen time and total sitting time were independently associated with increased mortality risk, while standing, walking, and MVPA were associated with decreased mortality risk
Summary
Sedentary behaviour, sleeping, and physical activity are thought to be independently associated with health outcomes but it is unclear whether these associations are due to the direct physiological effects of each behaviour or because, across a finite 24-hour day, engagement in one behavior requires displacement of another. A 60-minute block of low-intensity walking will have different health effects depending on whether it displaces an equal amount of sitting, vigorous exercise, or brisk walking This limitation can be overcome by statistical modeling that estimates the effects of replacing one behaviour with another, the isotemporal substitution modeling [ISM] approach [10]. “sedentary time” in this study [12] did not distinguish between sitting and standing Another recent cross-sectional ISM study [11] found that replacing sedentary time with MVPA, but not with light-intensity activity, was linked to beneficial associations with a range of cardiometabolic markers. Such information has both clinical and public health relevance and may be valuable in developing more accurate and specific public health recommendations, clinical guidelines, and preventative or therapeutic interventions
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