Prolonged Bouts Of Sedentary Time Are Associated With Percent Body-fat, Independent Of Total Sedentary Time

Abstract

Sedentary behavior, particularly television viewing time, is detrimentally associated with several health outcomes, including obesity. However, studies have typically used self-reported measures of total sedentary time, without considering the impact of the duration of sedentary bouts. Animal studies suggest that longer, uninterrupted bouts of sedentary time have the most detrimental metabolic effects. PURPOSE: To determine if longer average bouts of sedentary time are associated with higher percent body-fat, independent of total sedentary time. METHODS: Sedentary time of participants (79 men, 118 women; mean age 51. 8y, SD 12.5) during waking hours on a single, non-work day (Sunday) was determined by accelerometry (Actigraph). Total sedentary time (counts/minute <100), as well as number of sedentary bouts, and mean sedentary bout time were determined. A sedentary bout was denned as the sum of minutes of <100 accelerometer counts. Percent body-fat was determined by bio-impedance analysis. RESULTS: Mean sedentary bout times (reflecting uninterrupted sedentary time) were 7.0 (SD 3.5) minutes in men, and 6.1 (2.3) minutes in women (t=2.12, p=0.035). After adjusting for age, moderate-to-vigorous intensity activity time, and total sedentary time, mean sedentary bout times were significantly associated with higher percent body-fat in women (b=1.09, 95% CI 0.16 to 2.03, p=0.02), but not men (b=0.28, −0.33 to 0.89, p=0.37). Similarly, the negative association of higher total number of sedentary bouts (reflecting more breaks in the time spent being sedentary) with percent body-fat approached significance in women (b=−0.07, −0.14 to 0.00, p=0.06), but not men (b=−0.05, −0.13 to 0.02, p=0.17). CONCLUSIONS: These findings provide preliminary evidence on the potential importance for human health of avoiding prolonged periods of being sedentary, independent of physical activity. The significant associations for women, but not for men, support findings from studies of the metabolic consequences of television viewing time. The biological and behavioral mechanisms that may underlie these associations warrant further investigation.