Vitamin D deficiency and insulin resistance in obese African-American adolescents.

OBJECTIVE: The study aim determined if low 25-hydroxy vitamin D levels correlated with low levels of adiponectin and insulin resistance in African American adolescents with body mass index > or = 85th %. PATIENTS AND METHODS: Fasting blood levels of adiponectin, 25-hydroxy vitamin D, insulin, glucose, lipid, leptin and glycosylated hemoglobin were measured in a total of 34 (19 study and 15 control) African American adolescents between the ages of 10 and 20 years. Nutritional vitamin D intake and body composition measurements were assessed. Insulin resistance was calculated using the homeostasis model assessment. RESULTS: Adiponectin, fasting insulin, glucose, leptin, triglycerides, HDL, and 25-hydroxy vitamin D levels all reached statistical significance in the group with body mass index > or = 85th percentile when compared to the control population. There was no difference in vitamin D intake between the two groups. CONCLUSIONS: Low vitamin D levels correlated with low adiponectin levels and obesity and insulin resistance.

Significance of plasma C-peptide in obese African American adolescents.

BACKGROUND: C-peptide blood levels can indicate whether or not a person is producing insulin and roughly how much. C-peptide is secreted as a byproduct of the biosynthesis of insulin from proinsulin. C-peptide has proposed biological activity and a well-established diagnostic value. The significance of C-peptide concentration in the plasma and urine in the pediatric population needs further delineation. AIM: To determine the significance of plasma C-peptide in obese African American adolescents with mild insulin resistance but no evidence of diabetes. METHODS: This study included 19 African American adolescents with body mass index (BMI) in at least the 85th percentile evaluated with anthropometric measurements, Homeostatic Model Assessment-Insulin Resistance (HOMA-IR) score, and oral glucose tolerance test (OGTT), and 24-hour urine collections. The study also included an age-matched control group of 15 healthy African American adolescent controls and were not subjected for OGTT. The correlation among BMI, fasting plasma C-peptide concentrations, and 24-hour-urine C-peptide concentrations was calculated. T Tests were conducted to compare plasma C-peptide and 24-hour-urine C-peptide concentrations for the test group and controls. RESULTS: Mean HOMA score (3.96 +/- 1.84) signified mild insulin resistance among the adolescent test group. The test subjects exhibited adequate glucose tolerance (glucose range, 89.4-122.5 mg/dL) during the OGTT. A significant positive relationship was observed between BMI and fasting plasma C-peptide concentration in the control group (r = 0.537) but not the test group (r = 0.335). An insignificant positive relationship was exhibited between BMI and 24-hour-urine C-peptide concentration in the test group (r = 0.150) and controls (r = 0.254). CONCLUSIONS: The positive relationship among BMI, plasma C-peptide, and urine C-peptide is worth further evaluation in studies conducting multiple rounds of OGTT with a larger sample of pediatric subjects. The potential diagnostic value of C-peptide may facilitate early detection of insulin resistance in the pediatric population.