Association between bone lead levels and aggression in the birth to twenty plus cohort

Tlotleng, Nonhlanhla
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Background: Environmental lead exposure has been associated with a number of adverse health outcomes in children including behaviour problems. While the association between blood lead levels and aggression has been investigated in children and adolescent youth in South Africa, there are limited studies that have assessed health outcomes associated with cumulative bone lead levels. Therefore, the aim of this secondary analysis was to assess the association between bone lead levels and aggressive behaviour among the youth in South Africa.Methods: This study was a secondary analysis from the Birth to Twenty Plus Cohort conducted in Johannesburg-Soweto metropolitan area. In this study, bone lead levels of men and women were measured using K-Shell X-ray Fluorescence (KXRF). The Buss Perry Aggression questionnaire was administered to study participants to measure their aggression behaviour as a score. Data on demographic, socioeconomic factors, and psychosocial factors were obtained using a structured questionnaire. Linear regression models were fitted with continuous bone lead levels as the independent variable and the four scales of aggression adjusting for known study confounders. Furthermore, structural equation modelling (SEM) was used for path analysis to assess direct and indirect pathways in the association between bone lead and aggression.Results: Overall, there were 100 participants in this study, 53 males and 47 females aged 23 (n=77) and 24 (n=23) year olds. Most of the participants had secondary education (n=61), and a few achieved tertiary education (n=17). The linear regression models showed that bone lead levels were associated with the aggression score for anger (p=0.017), but not associated with physical aggression, verbal aggression and hostility. When the total aggression score was used as the dependent variable there was no association with bone lead levels. Nonetheless, the models showed that as bone lead levels increased there is an increase in the score for aggression. Psychosocial factors such as a history of family violence and exposure to neighbourhood crime were found to be significant predictors for aggression. Path analysis using SEM showed a significant direct effect between maternal education and bone lead levels (p<0.001) were a higher level of maternal education was found to decrease bone lead levels. Conclusion: This study showed that bone lead levels was associated with aggression score for anger. While a larger sample size may be necessary to further investigate the association between bone lead levels and aggression, the findings from this study provides a preliminary overview in the relationship of these important public health factors. This information may be crucial in the drafting of policies designed to combat crime associated with youth aggression in South Africa.
A research report submitted in partial fulfilment of the requirements for the degree of Master of Science in Epidemiology (Epidemiology and Biostatistics) to the Faculty of Health Sciences, School of Public Health, University of the Witwatersrand, Johannesburg, 2020