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Soren Snitker, MD, PhD; Katherine Y. Le, MPH; Erin Hager, BS; Benjamin Caballero, MD, PhD; Maureen M. Black, PhD

Arch Pediatr Adolesc Med. 2007;161(7):677-683.

Objective  To examine how body composition and physical activity are related to insulin sensitivity and secretion in adolescents.

Design  Cross-sectional.

Setting  Baltimore, Maryland.

Participants  Fifty-six healthy adolescents (34 boys and 22 girls; mean [SD] age, 13.3 [1.3] years; 95% were African American) who had been recruited at infancy from a health care clinic serving a low-income, urban community.

Main Exposures  Physical activity was measured for 5 to 7 days by a uniaxial accelerometer placed on the right ankle. Proportion of time spent in play-equivalent physical activity (PEPA) was defined as 1800 or more counts per minute. Body mass index (BMI) (calculated as weight in kilograms divided by height in meters squared) was converted to an age- and sex-specific z score.

Main Outcome Measures  Insulin sensitivity, insulin secretion, and disposition index calculated from a fasting oral glucose tolerance test.

Results  Thirty-nine percent of the adolescents had a BMI in the 85th percentile or higher; half of those were overweight (BMI  95th percentile). Play-equivalent physical activity and BMI z score were not correlated. In multivariate analyses, BMI z score and time spent in PEPA together explained 21% of the variance in insulin sensitivity and 18% in insulin secretion. Independent of each other, high BMI z score and low proportion of PEPA were significantly associated with low insulin sensitivity (partial r² = 0.14 and 0.10, respectively) and high insulin secretion (partial r² = 0.10 and 0.10, respectively), but not with disposition index.

Conclusions  In a cohort of urban, predominantly African American adolescents, both body composition and physical activity were independently associated with insulin sensitivity. At this point, insulin secretion is appropriately regulated.

Author Affiliations: Departments of Medicine (Drs Snitker and Black) and Pediatrics (Drs Snitker and Black and Mss Le and Hager), University of Maryland School of Medicine, and Center for Human Nutrition, Department of International Health, Johns Hopkins Bloomberg School of Public Health (Ms Hager and Dr Caballero), Baltimore.