Racial differences in insulin secretion and sensitivity in prepubertal children: Role of physical fitness and physical activity

Objective: To investigate in prepubertal children whether physical fitness and/or physical activity are: 1) associated with insulin secretion and sens itivity and 2) account for racial differences in insulin secretion and sens itivity. Research Methods and Procedures: Subjects included 34 African American and 34 white nondiabetic children aged 5 to 11 years. Data were divided into tw o sets according to the availability of VO2max and physical activity data. Body composition was measured by dual-energy X-ray absorptiometry, Subcutan eous abdominal adipose tissue and intraabdominal adipose tissue were examin ed by computed tomography. Insulin sensitivity (S-I) and acute insulin resp onse (AIR) were determined by a frequently sampled intravenous glucose tole rance test. An all-out, progressive treadmill exercise test was used for me asuring VO2max. Physical activity data were collected by questionnaire. Results: African American children had lower S-I and higher AIR than white children, after adjusting for total body fat mass. African Americans report ed higher levels of physical activity (hours/wk) than whites, but had a low er VO2max. In multiple linear regression analysis, hours/wk of activity and hours/wk of vigorous activity, but not moderate activity, were independent ly related to S-I and AIR after adjusting for race, total body fat mass or fat distribution, and total lean tissue mass. VO2max was not related to AIR , and was inversely related to S-I, after adjusting for body composition. R ace remained significantly associated with both S-I and AIR, even after adj usting for body composition, fat distribution, and hours/wk of activity or hours/wk of vigorous activity. Discussion: In summary, overall physical activity and, especially, vigorous activity were associated with insulin secretion and sensitivity. However, neither physical activity nor VO2max explained the racial difference in ins ulin secretion (higher in African Americans) and sensitivity (lower in Afri can Americans), Thus, racial (African American to white) differences in asp ects of insulin action seem to be due to factors other than body compositio n, fat distribution, cardiovascular fitness, and amount of physical activit y.