Comparison of waist circumference distribution of South African black children from different study populations
Motswagole, Boitumelo Stokie
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Studies in both children and adults indicate that waist circumference (WC), a measure of abdominal obesity is closely related to cardiovascular risk factors. The accurate identification of abdominally obese children in health screening programmes for early intervention is of importance. There are, however, concerns about using international definitions for screening purposes because in most instances these have been derived from Western populations and, therefore, may have limited usefulness to children in other parts of the world. When these cut–off points are used in developing countries, they ignore the fact that the growth patterns of children and burdens of disease vary between countries. Due to lack of population specific cut–off points for children in the developing world it may be tempting and convenient to use the same cut–off points as for children in developed countries, but such a practice runs the risk of exporting failure. Ideally, a screening tool should have both high sensitivity and specificity, and these are important considerations in choosing the definition for the detection of childhood abdominal obesity. High sensitivity is necessary to avoid failure of identifying obese children and high specificity of the screening tool ensures that non–obese children are not misclassified as obese, which may otherwise lead to unnecessary treatment and psychosocial implications of stigmatisation. Failure to identify the abdominally obese child may have more serious consequences than misclassification, since it results in an increase in adult morbidity and mortality. Therefore, the main aim of this thesis was to examine fat distribution patterns of black South African (SA) children in relation to health risk. The specific objectives were to: compare the body composition of black stunted and non–stunted children from two rural communities in South Africa; to describe and compare the age and sex specific WC percentile distribution for black SA children from different study populations and compare the WC percentile distribution with those for African–American (A–A) children and to assess the diagnostic accuracy of waist–to–height ratio (WHtR) as a marker for high blood pressure, a cardiovascular risk factor in SA children. Findings of this study demonstrated increased total adiposity in non–stunted children, but trends of increased central adiposity, measured as WHtR in stunted children. This warrants further investigation on this relationship among children older than 13 years in the African context where many children are stunted. The differences observed between the different data sets and between SA and A–A children suggest that nationally representative data should be used to develop age, sex and ethnic specific WC percentiles for this population. The results indicate clearly that the median WC of children from SA studies is smaller than those of A–A children, with a medium to large effect size for the difference. Results also suggest concern with respect to high WC values (> 80 cm) among some children. The recommended universal WHtR cut–off value of 0.5 for assessment of cardiovascular risk is not suitable for black SA children because it had low sensitivity in predicting high blood pressure. The absence of locally developed cut–off values for WC and WHtR for children warrants research due to the associations between being overweight and obese and disease outcomes. It is fundamental to detect risk at an early stage so that appropriate intervention can be initiated timeously.
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