Association of physical activity and body composition with insulin sensitivity in a community sample of adolescents

Abstract

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 r(2) = 0.14 and 0.10, respectively) and high insulin secretion (partial r(2) = 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.