More time spent sedentary has been associated with an increased risk of death. We can offset this risk increase by moving more vigorously when we’re not being sedentary, but how much moderate-to-vigorous physical activity (MVPA) is needed differs between studies using different experimental methods. Moreover, many of those studies based their conclusions on self-reported activity levels, which are unreliable. By contrast, this study used data collected from accelerometers.

The study

This meta-analysis of 9 studies from four different countries included 44,350 adults whose physical activity was measured via accelerometers over periods of 4 to 14.5 years. The main objective was to examine the associations between all-cause mortality and different combinations of MVPA and sedentary time. As a secondary objective, the authors asked whether vigorous physical activity could offset the increase in mortality risk (i.e., risk of death) caused by more time spent being sedentary.

The results

Depending on the study, the average daily sedentary time ranged from 8.5 to 10.5 hours (not counting sleep), whereas the average daily MVPA time ranged from 8 to 35 minutes.

When the group with the highest physical activity and lowest sedentary times was compared to groups with lower MVPA levels and higher sedentary time, the risk of death was higher with lower MVPA and higher sedentary time. In short, the risk of death was raised by sedentariness and reduced by exercise.

For the participants with the highest third of MVPA, the association between greater sedentary time and risk of death was attenuated, although not completely eliminated. This suggests that increased physical activity can offset some of the risk associated with sedentary behavior. In contrast, participants in the lowest third of MVPA had a greater risk of death regardless of sedentary time.

These results suggest that while more time spent being sedentary is associated with an increased risk of death, this risk increase can be partially offset by 30 to 40 minutes of moderate-to-vigorous physical activity per day.

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This Study Summary was published on January 5, 2021.