Adults can spend an average of 9-10 hours sitting every day which is mostly during work hours in developed nations. Unfortunately, a highly sedentary lifestyle has been shown in much research to be associated with a heightened risk of death. Previous research on the benefits of physical activity to counter this has relied on aggregated data, which can result in less generalizable results. This study tried to overcome this by pooling individual data from four groups of people wearing activity trackers to examine the effects of physical activity on sedentary time and death, and vice versa, as well as what amount of time might influence risk.
The researchers included data collected between 2003 and 2019 from the Norwegian Tromsø Study 2015–16; the Swedish Healthy Ageing Initiative (HAI) 2012–19; the Norwegian National Physical Activity Survey (NNPAS) 2008– 09; and the US National Health and Nutrition Examination Survey (NHANES) 2003–06. From this, 12,000 participants who were at least 50 were included in the analysis. Participants had at least 4 days of 10 daily hours recorded by activity trackers, were monitored for at least 2 years, and provided information regarding various potentially influential factors.
Overall, 5943 participants spent less than 10.5 hours being sedentary, and 6042 spent more than 10.5 hours sitting down every day. During an average period of five years, 805 participants died, of whom 357 spent under 10.5 hours being sedentary every day, and 448 spent more than 10.5 hours sitting down every day. Higher amounts of daily moderate to vigorous daily physical activity was associated with a lower risk of death irrespective of the amount of sedentary time, and the association between sedentary time and death was largely influenced by the amount of physical activity.
The analysis revealed that more than 22 minutes of moderate to vigorous physical activity every day was associated with a lower risk of death. An extra 10 minutes per day was associated with a 15% lower risk of death in those with less than 10.5 hours of daily sedentary hours, and a 35% lower risk among those spending more than 10.5 hours sitting every day. However, light-intensity physical activity was only associated with a lower risk of death among those who were highly sedentary spending more than 12 hours a day sitting.
Due to the nature of observational studies, the results can not establish cause and effect. This study was also not without limitations such as not being able to repeat measures of physical activity and sedentary hours to preclude any changes over time, activity trackers may not have correctly classified all activity types, and there may have been other potentially influential factors that weren’t accounted for.
Despite this, the researchers concluded: “Small amounts of MVPA [moderate to vigorous physical activity] may be an effective strategy to ameliorate the mortality risk from high sedentary time, where accumulating more than 22 mins of MVPA eliminates the risk of high sedentary time. Efforts to promote physical activity may have substantial health benefits for individuals.”
