Adolescent physical activity, sedentary behavior and sleep in relation to body composition at age 18 years in urban South Africa, Birth-to-Twenty+ Cohort.

BACKGROUND: Adolescence is marked by a decline in physical activity, rapid physical growth and changes in body composition, which have been linked to body composition. Prospective data on these associations are rare, particularly in Africa. AIM: The aim of this study was to examine the association of longitudinal patterns across adolescent in physical activity, sedentary behavior and sleep, with anthropometry and body composition at age 18 years in urban South Africa. METHODS: We analyzed data from the Birth-to-Twenty Plus Cohort (Bt20+), a longitudinal study of children born in 1990 in Soweto-Johannesburg, South Africa. We used general linear models to investigate the association of adolescent (ages 12 to 18 years) longitudinal trends in physical activity, sedentary behavior and schoolnight sleep and overall physical activity patterns, with body mass index (BMI), waist circumference, fat mass index (FMI), lean mass index (LMI) and percent body fat at age 18 years. RESULTS: The final study sample included 1337 participants with anthropometric measurements (52% female) and 958 participants with body composition measurements (53% female). Males who were consistently more active and consistently walked to school over adolescence had lower waist circumference (B = - 2.0, 95% CI: - 3.9 to - 0.2), FMI (B = - 0.8, 95%: CI: - 1.2 to - 0.1) and percent body fat (B = -2.9, 95% CI: - 4.9 to - 0.9) at age 18 years than those who decreased activity and did not walk to school. Consistently-sedentary females had higher waist circumference than those whose sedentary behavior increased over adolescence (B = 5.4, 95% CI: 0.2 to 10.6). Males who reported sleeping 9 h or more per night on schoolnights had significantly lower BMI (B = -1.0, 95% CI: - 1.4 to- 0.5), and percent body fat (B = -1.5, 95%CI - 2.8 to - 0.1) than those who reported sleeping 8 h or less per night. CONCLUSION: Patterns of adolescent physical activity, sedentary behavior and sleep are related to young-adult body composition in urban South Africa. These modifiable behaviors may be paths for public health interventions to curb overweight and obesity in many low- or middle-income countries.

Longitudinal patterns of physical activity, sedentary behavior and sleep in urban South African adolescents, Birth-To-Twenty Plus cohort.

BACKGROUND: Adolescence is a critical phase of human development that lays the foundation for health in later life. Of the 1.8 billion adolescents in the world, roughly 90% live in low and middle-income countries. Yet most longitudinal studies of adolescent physical activity, sedentary behavior, and sleep come from high-income countries. There is a need for a better understanding of these behaviors to inform obesity and chronic disease prevention strategies. AIMS: The aim of this study is to identify longitudinal patterns and associations between physical activity, sedentary behavior and sleep in urban South African adolescents. METHODS: We analyzed data from the Birth-to-Twenty Plus Cohort (Bt20+), a longitudinal study of children in Soweto, Johannesburg, South Africa. Behaviors were self-reported annually between ages 12 and 17 y. We used Latent Class Growth Analysis to group participants into classes based on common longitudinal trajectories of time spent in informal physical activity, organized sports, walking to and from school, sedentary behavior, and school-night and weekend sleep, respectively. We performed group-based multi-trajectory modeling to identify latent clusters of individuals who followed similar trajectories of informal physical activity, organized sports and walking to and from school, and who followed similar trajectories of these three domains together with sedentary behavior and sleep. RESULTS: The large majority of males (82%) and all females failed to meet the World Health Organization (WHO) physical activity recommendation for adolescents of 60 min of moderate-vigorous intensity physical activity per day. The physical activity domains clustered together in three multi-trajectory groups that define individuals' overall physical activity pattern. While two patterns indicated decreases in physical activity throughout adolescence, one pattern, including 29% of the sample in males and 17% of the sample in females, indicated higher levels of activity throughout adolescence. Sedentary behavior and sleep trajectories did not cluster together with the physical activity domains. CONCLUSION: Most adolescents in this South African population did not meet WHO recommendations for physical activity. In this population, trajectories of sedentary behavior and sleep were independent of physical activity.

Stunting at 24 Months Is Not Related to Incidence of Overweight through Young Adulthood in an Urban South African Birth Cohort.

Background: The role that childhood stunting plays in the development of overweight and obesity later in life is not well understood, particularly in adolescence and young adulthood, because most studies have only followed up through midchildhood. Objective: The objective of this study was to examine the relation between stunting and age-specific patterns of overweight and obesity incidence from early childhood to young adulthood in the context of a country in the process of the nutrition transition while these children were growing up. Methods: We analyzed data from 895 participants in the Birth-to-Twenty Plus Cohort (Bt20+), an urban South African birth cohort initiated in 1990. Anthropometric data were collected at multiple ages and participants were included if they provided height at age 24 mo and ≥1 measure of body mass index [BMI; weight (kg)/height (m)2] in each of the following time periods: 4-8 y, 11-12 y, 13-15 y, 16-18 y, and 22-24 y. We defined stunting at age 24 mo as height-for-age z score <2 and overweight as BMI z score (BMIZ) >1 in childhood (4-8 y) and adolescence (11-12 y, 13-15 y, and 16-18 y) and BMI ≥25 in young adulthood (22-24 y). We compared BMI, BMIZ, and the prevalence of overweight by stunting status, stratified by sex. Results: Our sample was 93% black and 51% female. The prevalence of stunting at 24 mo was 26% in males and 19% in females. In young adulthood, the prevalence of overweight and obesity was 15.5% (men) and 47.5% (women). Among both males and females, neither mean BMI nor a combined measure of overweight and obesity in any subsequent period differed by stunting status at 24 mo (P ≥ 0.05). Conclusion: Stunting at 24 mo was not related to the risk of overweight or obesity in this cohort. Stunting may not be an important contributor to the increasing obesity rates in urban South Africa.