Trajectories of activity and sleep through adolescence and body composition at age 18 years: Birth to Twenty Plus Open Access

Hanson, Sara (Spring 2020)

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Background: Adolescent physical activity, sedentary behavior and sleep are modifiable behaviors that have been linked to body composition, but prospective data on these behaviors following up to adulthood are rare, particularly in low and middle-income countries. South Africa has one of the highest prevalences of overweight and obesity in Sub-Saharan Africa, with 39% of men and 69% of women affected.

Aim: This dissertation has 2 aims. First to add to the very limited longitudinal data on physical activity, sedentary behavior and sleep change with time from adolescents living in Africa. Second, to offer new insights into the current overweight and obesity epidemic in South Africa by examining the association of these adolescent behaviors with body composition at age 18 years.

Methods: We analyzed data from the Birth-to-Twenty Plus Cohort (Bt20+), a longitudinal study of children in Soweto, Johannesburg, South Africa. We performed Latent Class Growth Analysis to group participants into distinct classes based on common longitudinal trajectories of minutes per week spent in informal activity, organized sports, walking to and from school, sedentary behavior, school-night sleep and weekend sleep from ages 12-17 years. We used group-based multi-trajectory modeling to summarize overall physical activity patters in terms of the 3 physical activity domains. We used general linear models to investigate the associations of adolescent physical activity, sedentary behavior and sleep with anthropometry and body composition at age 18 years.

Results: The majority of males (82%) and all females failed to meet the World Health Organization (WHO) physical activity recommendation for adolescents of 60 minutes of moderate-vigorous intensity physical activity per day. While most experienced a declining overall physical activity pattern, 29% of the sample in males and 17% of the sample in females were consistently active throughout adolescence. Being consistently physically active and getting more sleep per night throughout adolescence was associated with more favorable body composition at age 18 years in urban South African males. Being more sedentary over adolescence was associated with less favorable anthropometric measurements in urban South African females.

Conclusion: Adolescent physical activity, sedentary behavior and sleep are modifiable behaviors that may be contributing to the prevalence of overweight and obesity in urban South African adults. 

Table of Contents

Part 1. Introduction, Literature Review, and Methodology

1        Chapter 1: Introduction 1

1.1  Rationale 2

1.2  Aims and Objectives 3

1.2.1        Overall Aim

1.2.2        Specific Objectives

1.3  Conceptual Model and Theoretical Framework 5

1.4  Dissertation Overview and Structure 6

2        Chapter 2: Literature Review 7

2.1  Adolescence 7

2.1.1        Physical Growth and Sexual Maturation

2.1.2        Brain Development and Psychosocial Changes

2.1.3        Impact of Adolescent Health Across the Life-course

2.2  Overweight and Obesity 8

2.2.1        Global Overweight and Obesity

2.2.2        Low and Middle-Income Countries

2.2.3        South Africa

2.2.4        Modifiable Risk Factors of Overweight and Obesity

2.3  Physical Activity 10

2.4  Sedentary Behavior 13

2.5  Sleep 14

2.6  Key Questions Still Outstanding 17

2.7  References for Chapters 1 and 2 19

3        Chapter 3: Overview of Methodological Approaches 25

3.1  Study Setting and Design 25

3.2  Dissertation Data 26

3.2.1        Primary Exposures and outcomes

3.2.2        Participant characteristics, predictors and covariates

3.2.3        Inclusion and Exclusion

3.3  Statistical Analyses 31

3.3.1        Trajectory Analyses   Latent Class Growth Analysis   Group Based Dual Trajectory Modeling

3.3.2        Overall Analysis Plan

3.4  References for Chapter 3 36

Part 2: Empirical Chapters

4        Chapter 4. Longitudinal patterns of Physical Activity, Sedentary Behavior and Sleep in Urban South African Adolescents, Birth-To-Twenty Plus Cohort 40

4.1  Abstract 42

4.2  Background 43

4.3  Methods 44

4.4  Results 49

4.5  Discussion 52

4.6  Conclusion 58

4.7  References 59

4.8  Tables and Figures 63

5        Chapter 5: Adolescent Physical Activity, Sedentary Behavior and Sleep in Relation to Body Composition at Age 18 years in Urban South Africa, Birth-To-Twenty Plus Cohort 84

5.1  Abstract 86

5.2  Background 87

5.3  Methods 88

5.4  Results 91

5.5  Discussion 95

5.6  Conclusion 99

5.7  References 100

5.8  Tables and Figures 103

Part 3: Discussion and Implications

6        Chapter 6: Discussion 116

6.1  Consolidated Findings 116

6.2  Overall Story 118

6.3  Strengths and Limitations 122

6.4  Future Research 123

6.5  Public Health Implications 124

6.6  Conclusions 125

6.7  References for chapter 6 126

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