Sleep, sedentary behavior, and physical activity in Brazilian adolescents: Achievement recommendations and BMI...

Physical activity, sedentary behavior (SB), and sleep are habitual human behaviors (HHB) which are modifiable throughout the different life phases. Therefore, it is necessary to analyze how the time distribution throughout the day among HHB may be associated with body mass index (BMI). These results could provide inferences which can guide interventions that trigger changes in adolescent behaviors in favor of their health. The objective of this study was to verify the proportion of adolescents who meet the recommendation of sleep, moderate to vigorous physical activity (MVPA), and screen time (ST); to analyze the associations between HHB and BMI, and to determine possible changes in BMI associated with time reallocation between different HHB. Daily HHB recommendations (yes/no) were analyzed by frequency distribution. Compositional data analyses were used to examine the association between HHB and the BMI z-score (zBMI) with covariates (sex, age, and socioeconomic status). Compositional isotemporal substitution models estimated the change in zBMI associated with HHB reallocations from 15 to 120 minutes. A total of 185 adolescents were included (15 to 18 years, 50.8% boys). Thus, total sleep time, SB, light physical activity (LPA) and MVPA were measured by 24-hour accelerometry for seven consecutive days. ST, demographic characteristics, and socioeconomic status were assessed using a questionnaire. Sleep, MVPA, and ST recommendations were achieved by 32.97%, 8.10%, and 1.08% of the sample, respectively. No adolescent was able to achieve all of the daily recommendations. Age was significantly and positively associated with zBMI (p<0.001). Simply replacing 75, 90, and 120 minutes of MVPA by LPA led to an estimated significant increase in zBMI (95CI% z-value, 0.01 to 1.49). The HHB relocation estimates in 24h did not show positive effects on zBMI, nor did it increase the time engaged in MVPA, which may raise the hypothesis that other parameters related to obesity and their related interactions need to be better understood.