Análises composicionais de atividade física, comportamento sedentário e tempo de sono em ciclos de 24 horas e seu efeito transversal e longitudinal na adiposidade de adolescentes

Abstract

Obesity, characterized mainly by excess body fat, is considered a global public problem on the rise, having tripled in the last four decades. The fundamental cause of excessive accumulation of body fat is energy imbalance, but several other factors contribute to weigtht accumulation, including behaviors aspects such as physical activity, sedentary behavior and sleep. These behaviors have long studied individually. However, recent literature has started to point out the interrelation of these behaviors and that, as they are codependent, they should be studied as such. Thus, compositional data analysis emerged, a new analytical approach that seeks to understand the simultaneous retationship of physical activity, sedentary behavior and sleep with health. Associated with this approach, a technique called compositional isotemporal substitution the effects on the health outcome. Thus, this dissertation aimed to investigate the effects of time reallocations between movement behaviors in 24-hour cycles on body adiposity in adolescents using a compositional data approach and isotemporal substitution. For this atudy, cross-sectional and longitudinal analysis were estimated by wrist accelerometers and together they formed 24-hour cycle, which was the exposure used. The outcome was percentage of body fat estimated by dual-energy-xray-absorptiometry (DEXA). Initially, descriptive analysis were carried out to characterize the sample and, to deal with the collinearity of behaviors, compositional data analysis was used. The 30 minute compositional isotemporal substitution was also used to reallocate time between behaviors and applied linear regression to estimate the effect of these changes on compositional of 24-hour cycles on adiposity in crude and adjusted analysis. Both the cross-sectional results at 15 years and the longitudinal results at 11 and 15 years raw demonstrated that the reallocation of time from moderate-to-vigorous physical activity to the other investigated behaviors (light physical activity, sedentary behavior and sleep) was associated eith na increase in the percentage of fat body and reverse reallocations, thst is, reallocations from other behaviors to moderate-to-vigorous physical activity were associated with a reduction in this indicator. However in the adjusted analysis, no association was observed. Considering several confounding factors, the results of this study demonstrated that there is no association between the reallocations of movement behaviors in the 24-hour cycle and body adiposity in adolescents.