The Compositional Effects of Time Spent in Sleep, Sedentary Behaviour and Physical Activity on Obesity in Children
Abstract Purpose Physical activity, sedentary behaviour (SB) and sleep have traditionally been studied as independent behaviours and not as co-dependent behaviours that are compositional in nature. This study used compositional data analyses to investigate the co-dependent relationships between time spent in movement behaviours (sleep, SB, light intensity physical activity (LIPA), and moderate-to-vigorous physical activity MVPA)) and obesity among children. Methods 434 children aged 10-13 years were studied. Participants wore an Actical accelerometer for 7 days to determine time spent in SB, LIPA, and MVPA. Time spent sleeping was determined from the accelerometer and a log. The outcomes of interest were the body mass index, waist circumference, and fat mass index. Compositional data analysis was used to examine associations. This involved transforming the movement behaviours using an isometric log ratio transformation, using regression to model the associations, and back-transforming the regression coefficients to estimate how displacing time from one movement behaviour with another influenced the obesity measures. Results The composition of movement behaviours was associated with all three obesity measures (p<0.001). Relative to the other movement behaviours, time spent in MVPA was negatively associated with the obesity measures (p<0.01), time spent in LIPA was positively associated with the obesity measures (p<0.05), while time spent in SB and sleep were not associated with the obesity measures. The most meaningful time displacements were for MVPA, and these displacements were larger at lower MVPA levels. For example, reallocating 10 minutes of MVPA to 10 minutes of LIPA was associated with a 2.7% (95% CI: 2.4, 2.8), 2.0% (95% CI: 1.8, 2.1), and 1.5% (95% CI: 1.4,1.6) increase in BMI z-score at the 25th, mean, and 75th MVPA percentiles, respectively. Conclusion The composition of movement behaviours across the day was associated with the obesity measures. The displacement of time from MVPA to LIPA were associated with the most significant changes in the obesity measures.
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