A longitudinal study examined the joint associations of sitting and physical activity with all-cause and CVD (cardiovascular disease) mortality in a large population sample of middle-age and older Australian adults. An additional purpose of the study was to examine the associations between sitting and mortality separately in each physical activity stratum. A secondary aim was to estimate the theoretical effects of replacing sitting with standing, physical activity, and sleep on mortality risk.
The researchers report that sitting is associated with all-cause and CVD mortality risk among the least physically active adults (those participating in physical activity less than 150 minutes of moderate to vigorous intensity physical activity (MVPA) per week.
The authors conclude that longer sitting times were associated with higher ACM and CVD mortality risk, but these associations were mostly restricted to people not meeting the physical activity recommendations. To redress this they suggest replacing sitting with walking and vigorous intensity physical activity is associated with the most consistent risk reductions. Reduction of sitting time is an important strategy, ancillary to increasing physical activity, for preventing cardiovascular disease and premature mortality in physically inactive populations (Source:.
The research has now been published in Journal of the American College of Cardiology
Background It is unclear what level of moderate to vigorous intensity physical activity (MVPA) offsets the health risks of sitting.
Objectives The purpose of this study was to examine the joint and stratified associations of sitting and MVPA with all-cause and cardiovascular disease (CVD) mortality, and to estimate the theoretical effect of replacing sitting time with physical activity, standing, and sleep.
Methods A longitudinal analysis of the 45 and Up Study calculated the multivariable-adjusted hazard ratios (HRs) of sitting for each sitting-MVPA combination group and within MVPA strata. Isotemporal substitution modeling estimated the per-hour HR effects of replacing sitting.
Results A total of 8,689 deaths (1,644 due to CVD) occurred among 149,077 participants over an 8.9-year (median) follow-up. There was a statistically significant interaction between sitting and MVPA only for all-cause mortality. Sitting time was associated with both mortality outcomes in a nearly dose-response manner in the least active groups reporting less than 150 MVPA min/week. For example, among those reporting no MVPA, the all-cause mortality HR comparing the most sedentary (more than 8 h/day) to the least sedentary (less than 4 h/day) groups was 1.52 (95% confidence interval: 1.13 to 2.03). There was inconsistent and weak evidence for elevated CVD and all-cause mortality risks with more sitting among those meeting the lower (150 to 299 MVPA min/week) or upper ( more than or equal to 300 MVPA min/week) limits of the MVPA recommendation. Replacing sitting with walking and MVPA showed stronger associations among high sitters ( more than 6 sitting h/day) where, for example, the per-hour CVD mortality HR for sitting replaced with vigorous activity was 0.36 (95% confidence interval: 0.17 to 0.74).
Conclusions Sitting is associated with all-cause and CVD mortality risk among the least physically active adults; moderate-to-vigorous physical activity doses equivalent to meeting the current recommendations attenuate or effectively eliminate such associations.
The full article is available from the Journal of the American College of Cardiology