1. Both a high total amount of sedentary time as well as its accumulation in lengthy, continuous stretches were linked to a higher risk of all-cause mortality.
2. Results suggest that guidelines for physical activity should be aimed at both decreasing and disrupting sedentary time in order to lower the risk of death.
Evidence Rating Level: 2 (Good)
Study Rundown: Past studies have shown evidence that sedentary time is linked to cardiovascular disease and mortality. However, most studies have depended on self-reported sedentary time data, which is susceptible to reporting bias and errors in measurement. This prospective cohort study used accelerometer data to collect objectively measured sedentary time data in order to analyze the relationship between sedentary time and all-cause mortality. Researchers found that sedentary stretches of 60 minutes or more was linked to a higher risk for all-cause mortality while sedentary stretches of 29 minutes or less was linked to a comparatively lower mortality risk. However, accrual of large amounts of sedentary time was found to be hazardous regardless of how often it was interrupted. Therefore, both the total amount of sedentary time and its accumulation in lengthy, continuous stretches were linked to all-cause mortality, which suggests that guidelines for physical activity should be aimed at both decreasing and disrupting sedentary time in order to lower the risk of death.
A strength of the study is that it provides some of the first experimental evidence concerning how frequently sedentary time should be disrupted. Limitations of the study include possible data undersampling, sedentary behavior being based only on intensity due to the accelerator’s inability to distinguish between postures, and that the participants may not be characteristic of the general population.
In-Depth [prospective cohort]: In this study of 7985 U.S. adults (black and white) ≥ 45 years of age, researchers measured sedentary time for 7 days using a hip-mounted accelerometer. The researchers analyzed sedentary time as a mortality prognostic risk factor, including whether or not total sedentary time being accumulated in short or long stretches of time was relevant for prognosis. The median follow-up was 4.0 years, during which 340 participants died. Sedentary behavior was equal to about 12.3 hours (77.4%, SD 9.4%) of a 16-hour waking day. The average length of a continuous sedentary period was 11.4 minutes (SD 8.1). A higher total amount of sedentary time and a longer average stretch of sedentary time (for both factors, p for overall effect < 0.001) was correlated with an increased risk for all-cause mortality regardless of age, sex, race, BMI or amount of moderate- to vigorous-intensity physical activity. Sedentary stretches of 29 minutes or less was linked to the lowest risk of death in the study participants, which suggests that disrupting sedentary time every half hour may assist in lessening the adverse effects of time spent sedentary.
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