Continuing the Debate Over Why Time Spent Sitting Correlates with Mortality
You might recall a number of epidemiological studies from the past fifteen years that examined correlations between time spent sitting and late life mortality. Some demonstrated that regardless of degree of physical activity sitting time still correlated with mortality - not the most intuitive of outcomes. As is the case for all such epidemiological questions of lifestyle and mortality, the general thrust of the data was disputed by a few large opposing studies. One in particular argued that the focus on sitting was misplaced, early studies misinterpreted their data, and that the focus should be on immobility. In support of that idea, accelerometer studies have consistently shown that low levels of activity, such as gentle walking, gardening, moving around in the house, are significantly better for long-term health than being entirely sedentary. Still, the debate on sitting continues, as shown here.
Sedentary behavior is a recognized mortality risk factor. The novel and validated convolutional neural network hip accelerometer posture algorithm highly accurately classifies sitting and postural changes compared with accelerometer count cut points. We examined the prospective associations of convolutional neural network hip accelerometer posture-classified total sitting time and mean sitting bout duration with all-cause and cardiovascular disease (CVD) death.
Women (n=5,856; 79±7 years old) in the Women's Health Initiative Objective Physical Activity and Cardiovascular Health (OPACH) Study wore the ActiGraph GT3X+ for ~7 days from May 2012 to April 2014 and were followed through February 19, 2022 for all-cause and CVD death. The convolutional neural network hip accelerometer posture algorithm classified total sitting time and mean sitting bout duration from GT3X+ output. Over a median follow-up of 8.4 years there were 1,733 deaths, 632 of which were from CVD. Adjusted Cox regression hazard ratios (HRs) comparing women in the highest total sitting time quartile (more than 696 minutes per day) to those in the lowest (less than 556 minutes per day) were 1.57 for all-cause death and 1.78 for CVD death. HRs comparing women in the longest mean sitting bout duration quartile (more than 15 minutes) to the shortest (less than 9.3 minutes) were 1.43 for all-cause death and 1.52 for CVD death. Apparent nonlinear associations for total sitting time suggested higher all-cause death and CVD death risk after ~660 to 700 minutes per day.
Higher total sitting time and longer mean sitting bout duration are associated with higher all-cause and CVD mortality risk among older women. These data support interventions aimed at reducing both total sitting time and interrupting prolonged sitting.