Reallocating Sedentary Time to Sleep or Physical Activity: Associations with BMI in College Students

IntroductionThe purpose of this study was to examine the effects of reallocating time spent in weekday sedentary behavior (SED) to sleep duration, walking activity, or moderate-to-vigorous physical activity (MVPA) on body mass index (BMI) in college students using an isotemporal substitution model. MethodsSelf-reported BMI (height and weight), sleep duration, weekday SED, walking activity, and MVPA were obtained using the Pittsburgh Sleep Quality Index and International Physical Activity Questionnaire. ResultsAmong participants (n = 1533, 20.1 +/- 1.5 yr old), sleep duration (r = -0.069) and MVPA (r = -0.069) were inversely associated with BMI (P < 0.01). Reallocating 60 min of weekday SED to sleep duration (B = -0.277; 95% confidence interval (CI): -0.462 to -0.092) or MVPA (B = -0.386; 95% CI: -0.626 to -0.147) was associated with lower BMI, with stronger associations observed among students with overweight/obesity. ConclusionGreater time spent in sleep and MVPA was associated with lower BMI, especially among overweight/obese college students. Lifestyle modifications should include reducing SED and increasing sleep and physical activity because these factors are associated with lower BMI.