Differences in body composition of black and white girls.

Adults have racial differences in body composition that may modulate risks resulting from obesity. Although black and white children have been shown previously to have differences in bone mineral density and subcutaneous body fat, differences in visceral adipose tissue have not been evaluated. We studied 20 black and 20 white normal-weight girls aged 7-10 y, who were matched for weight, body mass index (BMI), bone age, chronological age, Tanner breast stage, and socioeconomic status. Each underwent anthropometric measurements, bioelectrical impedance analysis, dual-energy X-ray absorptiometry (DXA), and abdominal magnetic resonance imaging (MRI) for determination of total (TAT), visceral (VAT), and subcutaneous (SAT) adipose tissue. Serum lipids and fasting and 2-h oral-glucose-tolerance test (OGTT) glucose and insulin concentrations were also measured. There were no differences between groups in absolute waist circumference or waist-to-hip ratio, but waist-to-thigh ratio was smaller in black than in white girls. Black girls had greater bone mineral density and less TAT, VAT, and SAT than whites. VAT was not significantly correlated with any measure of insulin, or with serum lipids. However, both basal and 2-h OGTT serum insulin were significantly correlated with SAT as assessed by MRI in black girls (r2 = 0.46 for basal insulin, P = 0.001: r2 = 0.31 for 2-h insulin, P = 0.01) but not in white girls (r2 < 0.05, for basal and 2-h insulin, NS). We conclude that there are significant racial differences in body composition and differences in the strength of association between abdominal adipose tissue depots and insulin sensitivity in black and white girls.

Differences in the hypothalamic-pituitary-adrenal axis of black girls and white girls.

After intravenous administration of ovine corticotropin-releasing hormone (CRH), the plasma corticotropin (ACTH) concentrations of adult black women and men are approximately twice as high as those of adult white women and men; however, there are no corresponding differences in cortisol response. To determine whether these differences in ACTH secretion are also present in prepubertal and early pubertal girls, we studied the hypothalamic-pituitary-adrenal axis of 19 black and 19 white girls of normal weight (age 7 to 10 years) who were matched for body mass index, age, and socioeconomic status. Measures of cortisol's effects, including waist circumference, waist/hip ratio, and fasting insulin and glucose levels, were obtained and related to the ACTH and cortisol responses to 1 micrograms/kg CRH. There were no racial differences in waist circumference, waist/hip ratio, fasting glucose or insulin levels, baseline free or total plasma cortisol levels, baseline ACTH concentrations, or the plasma cortisol response to CRH. However, CRH-stimulated plasma ACTH concentrations, measured in a polyclonal radio-immunoassay, were significantly greater in prepubertal and early pubertal black girls than in white girls at all time points between 15 and 90 minutes after administration of CRH (area under curve (AUC 1754 +/- 121 pmol/L/min in black girls vs 1304 +/- 124 pmol/L/min in white girls, p < 0.001). This difference was confirmed by an immunoradiometric assay believed to be specific for intact ACTH (AUC 1634 +/- 139 pmol/L/min in black girls vs 1224 +/- 104 pmol/L/min in white girls, p < 0.001). Neither ACTH AUC nor cortisol AUC was significantly correlated with body mass index in either black or white girls. We conclude that there are differences in the hypothalamic-pituitary-adrenal axis of prepubertal and early pubertal black and white girls similar to those found previously in adult women. The cause of these differences remains to be elucidated.