Determinants of pubertal development in an urban South African cohort
thesisposted on 31.01.2013 by Laura L. Jones
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Age at the initiation of puberty and at menarche are key maturational indicators. They reflect health both within and between populations; in that a declining average age is associated with improving health, nutrition, and socio-economic conditions. Knowledge of the timing of pubertal development and menarche is important as earlier development within a population, in particular, has been linked with an increased risk of negative sequelae including overweight and obesity, development of risk factors for non-communicable diseases such as hypertension and insulin resistance, and engagement in risk behaviours such as early sexual debut and substance abuse. The main aims of this study were to investigate the timing of, and the early life factors (such as body composition and growth velocities) associated with pubertal development and age at menarche in Black and White urban South African adolescents. Mixed-longitudinal data (n = 401) from the Birth to Twenty (Bt20) birth-cohort study, initiated in 1990 and set in SowetoJohannesburg, South Africa were used. Median age at the initation of puberty and at menarche was derived by fitting logistic curves to cumulative frequency plots. Logistic regression models were constructed to examine the early life predictors of the timing of puberty and menarche. Data were also collected from adolescents and Bt20 staff (n = 72) using focus groups to explore views on the pubertal development questionnaire used in the Bt20 study. Median age at the initiation of genitalia development was 10.4 years (95% Cl = 8.4, 12.4) for Black boys and 9.8 years (95% Cl = 9.4, 10.2) for White boys. Median age for the initiation of pubic hair development for Black males was 10.8 years (95% Cl = 9.6, 12.0) compared to White males, which was 10.2 years (95% Cl = 8.4, 12.0). Median age at the initiation of breast development in Black females was 10.1 years (95% Cl = 9.3, 10.9) compared to White females which was 10.2 years (95% Cl = 8.2, 12.2). Median age for the initiation of pubic hair was 10.3 years (95% Cl = 9.3, 11.3) and 10.5 years (95% Cl = 8.7, 12.3) for Black and White girls, respectively. Results from logistic regression showed that a greater weight and height velocity in late childhood significantly increased the odds of achieving early breasU genitalia development. Furthermore, a low socio-economic status (SES) index at 9/10 years significantly reduced the odds of achieving early breasUgenitalia development. A greater weight, height, body mass index (BM I), and growth rate during infancy and childhood significantly increased the odds of achieving early pubic hair development. Median age at menarche for Black females was 12.4 years (95% Cl = 12.2, 12.6) and 12.5 . years (95% Cl = 11.7,13.3) for White females. Average menarcheal age for Black girls has declined by 0.56 years per decade and 0.32 years for White girls in South Africa, when comparing the current study findings with those from previous studies. Results from logistic regression showed that being taller, fatter and heavier in late childhood significantly increased the odds of achieving earlier menarche. The focus groups provided a range of opinions relating to the Bt20 pubertal development questionnaire and procedure. The majority of views were positive and included the ease of understanding and completion of the tool. Negative views revolved around the language used and privacy issues. These qualitative results provided a unique insight into the way in which pubertal development data are assessed and how these methods can potentially be improved to enhance the reliability and accuracy of pubertal development data collection. The results from this study provide the most recent estimates of age at the. initiation of puberty and age at menarche for urban Black and White South African adolescents. This is particularly important given the social, nutritional, and economic transition currently occurring in this country as these key maturity indicators reflect population health. This study has also added to our knowledge of the factors that are associated with pubertal development, showing that proximate rather than distal factors are the most sensitive indicators in this urban transitioning environment. In addition, the results from the focus groups provided a unique insight into how pubertal development data are assessed and how these methods could be improved. The negative health outcomes which have been associated with earlier pubertal development and age at menarche are major public health concerns, particularly in the South African context given the HIV/AIDS epidemic and rising levels of obesity. This study highlights the need for renewed research and resources for intervention strategies and policy programmes which target appropriate sex and obesity education in urban South African children.
- Sport, Exercise and Health Sciences