In their article, van der Ploeg and colleagues1 report important new findings from a large population-based study of Australian adults. They show total sitting time to be associated prospectively with all-cause mortality after accounting for many likely confounding variables, including leisure-time physical activity.
Increasing physical activity in adult populations is central to the prevention of obesity and the major chronic diseases. Traditionally, the focus has been on encouraging individuals to participate in moderate-to-vigorous physical activity (“health-enhancing exercise”) during their discretionary time, with a more recent emphasis on physically active transportation.2 For example, an individual who does 30 minutes of brisk walking on most days of the week will have met the public health guideline on the minimum amount of activity required for health benefits. However, this still leaves some 15½ hours of nonexercise awake time each day during which, for many adults, sitting is the predominant stance. This is a consequence of the plethora of ways in which the physical, economic, and social environments have changed, particularly since the middle of the past century. These changes—in personal transportation, communication, workplace productivity, and domestic entertainment technologies—have been associated not only with decreased physical activity but also with increased time spent sitting.3