Race, gender and adiposity in children.

Obesity is now considered a global epidemic with adverse effects on health and well-being (1). Over the last four decades, both developed and developing countries have seen increased prevalence of overweight and obesity in infancy, childhood and adulthood (2). Global projections suggest that by 2030 over three billion adults may be overweight or obese (1). Additionally, the worldwide prevalence of childhood overweight and obesity is projected to increase with an expected 60 million children being affected by the year 2020 (3). Obesity in childhood tracks into youth and adulthood, thus making childhood obesity a major public health concern (4). The causes of obesity are multi-factorial and research conducted by scientists around the world have indicated that there are ethnic, gender, societal and cultural underpinnings driving this epidemic (5, 6). In order to determine precisely which of these factors has the greatest influence on the prevalence of obesity in children, we will need to conduct large multi-ethnic longitudinal studies from early infancy. Until such studies are conducted, however, much can be learnt from large cross-sectional studies with comparisons of putative obesogenic factors. Questions to be considered include whether race or gender differences in childhood obesity are influenced by genetic factors being displayed in an ‘obesogenic’ environment or whether there are hormonal and physiological changes which account for these differences. In this issue of the Journal, Goon and colleagues report on a study which assessed the differences in the body fat percentage, estimated from skinfold thickness measurements, in urban South African children, 9–13 years old, and compared gender and racial differences in adiposity (7). Their main findings were that Black-African children had higher percentage body fat than their White-African counterparts, and that girls had significantly higher values than males in all age groups. These findings support the notion that both ethnicity and gender have significant influences on adiposity, and adds to the body of research that show differences in adiposity between these groups in paediatric populations (6, 8). Racial and ethnic differences in obesity and adiposity have also been demonstrated in paediatric populations in the United States of America (USA), where non-Hispanic black and Hispanic groups report higher prevalence of overweight and obesity when compared with other racial and ethnic groups (8). In a study among children aged 8–19 years, there were significant differences in both body mass index (BMI) and per cent body fat when comparing non-Hispanic whites to non-Hispanic black boys and girls (9). In non-Hispanic black girls, BMI values were higher than non-Hispanic whites, however, this did not correspond to the same differences when the per cent body fat was measured using the dual-energy X-ray absorptiometry (DEXA) technique. The non-Hispanic black girls had lower per cent body fat values than their non-Hispanic white counterparts (9). In boys, non-Hispanic blacks had significantly lower per cent body fat and higher fat-free mass than their non-Hispanic white counterparts. This difference in results for the boys may in part be due to the greater accuracy of the DEXA measurement for assessing body composition and highlights that BMI alone may sometimes misclassify adiposity. Gender differences in body fat percentage were also reported in the study by Goon and colleagues, where in both ethnic groups, girls had higher body fat percentage than boys (7). Similar findings were observed in development of the body fat percentage curves for children in the USA as reported by Ogden and colleagues (10). When the National Health and Nutrition Examination Survey (NHANES) data were analysed, they found that girls had higher body fat percentages than boys, at all age groups from 8–19 years (10). A significant decrease in body fat was observed in boys as they entered puberty in the NHANES study, which continued until the late adolescence (10). This, however, was not seen in girls where there was a gradual increase in percentage body fat as they got older (10). Residence in an urban environment may also have a significant influence on adiposity, as urban children may have higher dietary intake of high fat and high caloric foods, and increased consumption of foods away from home (11– 13). In the Caribbean region, there have been reported differences in the prevalence of obesity between urban and rural children and between males and females. One study conducted in an older adolescent population (15–19 years old) reported that the prevalence of both overweight and obesity combined was 23% higher in the urban compared to From: Tropical Medicine Research Institute (Epidemiology Research Unit), The University of the West Indies, Kingston 7, Jamaica.