Body composition measurement in African and Caribbean children and its relationship with morbidity

The global increase in obesity prevalence has led to a surge in metabolic disease in both adults and children. Furthermore, the burden of obesity and its related morbidities is not equally distributed across the UK population, with those from minority ethnic groups particularly affected. Effective paediatric epidemiological monitoring and clinical referral requires improved tools for assessing body fatness, and other body composition measures related to metabolic disease are needed. Presently the body mass index (BMI) used to identify overweight and obesity suffers from poor sensitivity and specificity, leading to misclassification of children, especially those from minority ethnic groups. Additionally BMI gives no indication of body fat distribution. Assessment tools specifically for African and Caribbean childhood populations are lacking and the aim of this thesis was to develop a range of assessment tools specifically for this population group. This thesis comprised four studies. In the first study the equations in the Tanita BC-418 bioimpedance (BIA) system used to predict fat mass (FM) and appendicular skeletal muscle mass (SMMa) were re-validated using dual-energy x-ray absorptiometry (DXA) as the criterion method in a sample of 44 African and Caribbean children aged 5-18 years. FM (kg) and SMMa (kg) were quantified by DXA and linear regression analysis used to produce new equations based on height2 /impedance. The key findings from this study were that BIA generally under-estimated FM and over-estimated SMMa in this population group, irrespective of age and gender. In the second study, the corrected measures of FM and SMMa were applied to an existing dataset of 1,336 African/Caribbean children aged between 5-16y whose body composition had been measured using the Tanita BC418 system. Percentile charts for %FM, %FFM, SMMa (kg), %SMMa and SMMa/FMM x 100 were generated using the software LMS Chartmaker. In the third study, blood pressure percentile charts and tables were developed based on data (n, 900) extracted for African and Caribbean children aged 5-18 years from the Health Survey for England data archives, 1991-2008. The centile curves for the anthropometric measures revealed gender and age-related patterns which compared closely to equivalent charts for Caucasian children. Finally in the fourth study, percentile charts and tables for waist circumference (cm) were developed using the same sample population. The findings from these studies provide the tools and preliminary evidence to support the use of African-Caribbean specific references for body composition and blood pressure measures in children and youths in the UK. The overall conclusion from this thesis indicates that paediatric overweight and obesity varies across different ethnic groups and this variation needs to be considered in the context of obesity surveillance and clinical assessment which themselves are determined by national obesity policy formulation and implementation. These are the first body composition percentile charts for African and Caribbean children living in the UK. These charts should replace BMI charts used for obesity assessment in paediatric and epidemiological settings as they are better tools for assessing overweight, obesity and sarcopenia.