Differential Impact of Obesity on Glucose Metabolism in Black and White American Adolescents

Age, sex, and ethnic variations in serum insulin concentrations among U.S. youth: findings from the National Health and Nutrition Examination Survey 1999-2002

OBJECTIVE

Distributions of serum concentrations of insulin among adolescents and young adults are poorly understood in the U.S. The objective of this study was to describe the distribution of serum insulin across demographic characteristics of U.S. adolescents and young adults.

RESEARCH DESIGN AND METHODS

A total of 1,791 male and female subjects aged 12-19 years who participated in the National Health and Nutrition Examination Surveys for 1999-2002 were included in the analyses.

RESULTS

Among male participants, serum concentrations of insulin increased from age 12 to 14 years before decreasing. Among female participants, concentrations were highest at age 13 years before decreasing steadily through age 19 years. Among participants aged 12-17 years but not those aged 18-19 years, females had higher mean log-transformed concentrations than males (P, Wald, F = 0.038 and 0.125, respectively) after adjusting for age and ethnicity. After adjusting for age and BMI percentile, mean log-transformed concentrations were higher in African-American females aged 12-17 years than in white or Mexican-American participants. No significant ethnic differences were found among female participants aged 18-19 years or male participants aged 12-19 years. Concentrations of insulin increased strongly with increasing levels of BMI.

CONCLUSIONS

These results provide detailed information about serum concentrations of insulin in a representative sample of U.S. adolescents and young adults and may be useful to monitor future trends of this risk factor for diabetes and cardiovascular disease.

Hyperinsulinemia in african-american children: decreased insulin clearance and increased insulin secretion and its relationship to insulin sensitivity

African-American (AA) children are hyperinsulinemic and insulin resistant compared with American White (AW) children. This study investigated 1) whether AA/AW differences in insulinemia are associated with differences in insulin clearance; 2) whether dietary patterns, mainly carbohydrate and fat intake, play a role; and 3) whether the quantitative relationship between insulin sensitivity and secretion is similar between AA and AW children. Forty-four prepubertal children (22 AA and 22 AW) with comparable body composition and visceral adiposity were studied. All underwent a 3-h hyperinsulinemic (40 mU x m(-2) x min(-1))-euglycemic clamp to calculate insulin sensitivity and insulin clearance and a 2-h hyperglycemic clamp (12.5 mmol/l) to assess first- and second-phase insulin responses. Twenty-four-hour food recalls were analyzed for macronutrient intake. Insulin clearance (19.5 +/- 0.7 vs. 22.9 +/- 1.1 ml x min(-1) x kg(-1) fat-free mass [FFM]; P = 0.011) and insulin sensitivity were lower in AA versus AW children (14.8 +/- 1.0 vs. 18.9 +/- 1.4 micro mol x min(-1) x kg(-1) FFM; P = 0.021). Both insulin clearance and insulin sensitivity correlated inversely with dietary fat/carbohydrate ratio, which was higher in AA than in white children. Fasting C-peptide and insulin were higher in AA children with no difference in proinsulin levels. First- and second-phase insulin concentrations and glucose disposition index (insulin sensitivity x first-phase insulin) were higher in AA than in white children (12.8 +/- 2.1 vs. 7.2 +/- 0.6 micro mol. min(-1) x kg(-1) FFM; P = 0.019). In conclusion, the hyperinsulinemia observed in AA children is due to both lower insulin clearance and higher insulin secretion compared with their white peers. The quantitative relationship between insulin secretion and sensitivity is upregulated in AA children. This suggests that increased insulin secretion in AA children is not merely a compensatory response to lower insulin sensitivity. Dietary factors may have a role. Additional studies are needed to determine whether metabolic/nutritional factors, possibly mediated through free fatty acids, may play a role in the hyperinsulinism observed in AA children.

Evaluation of the insulin resistance syndrome in 5- to 10-year-old overweight/obese African-American children

OBJECTIVE

To characterize the insulin sensitivity of overweight and obese 5- to 10-year-old (Tanner stage 1-3) African-American children screened for participation in a diabetes prevention study and to identify the association of insulin sensitivity with obesity, hyperlipidemia, and hypertension.

RESEARCH DESIGN AND METHODS

Measures of insulin resistance (homeostasis model assessment) and insulin sensitivity (Matsuda and DeFronzo's whole-body insulin sensitivity) were calculated from a 2-h oral glucose tolerance test in 137 African-American children recruited into a diabetes prevention study. Measures of lipids (LDL, HDL, total cholesterol, and triglycerides), blood pressure, and body composition were obtained for a subset of the children.

RESULTS

In response to a glucose challenge, girls and older and heavier children produced significantly more insulin. As BMI increased, there was a statistically significant decrease in insulin sensitivity, particularly in girls. Insulin sensitivity was inversely correlated with increases in blood pressure, triglycerides, subcutaneous fat, the percentage of total body fat, and Tanner stage, but it was not correlated with LDL and HDL.

CONCLUSIONS

Reduced insulin sensitivity and the cluster of risk factors known as the insulin resistance syndrome (IRS) are already apparent in these overweight African-American children. Young African-American girls, in particular, already show evidence of hyperinsulinemia in response to a glucose load, suggesting that the early stages of metabolic decompensation that lead to type 2 diabetes are already occurring. Monitoring of those risk factors known to be part of IRS should become part of routine medical care for overweight or obese African-American children.