Share this article on:

The Relation of Fatness to Insulin is Independent of Fitness in 9- but Not 15-yr-olds


Medicine & Science in Sports & Exercise: January 2008 - Volume 40 - Issue 1 - p 43-49
doi: 10.1249/mss.0b013e31815988d7
BASIC SCIENCES: Epidemiology

Purpose: To explore the relationship between varying aerobic fitness (fitness), fatness, and fasting insulin levels in healthy children.

Methods: A population-based sample of 9-yr-old (9YO, 47 boys, 56 girls) and 15-yr-old (15YO, 53 boys, 51 girls) Icelandic children. Body fatness was evaluated via body mass index, waist circumference adjusted for height (waistadj), and sum of four skinfolds. Fitness was assessed with a graded maximal cycle ergometer test. Fasting insulin was measured using an ECLIA.

Results: Fasting insulin correlated to all fatness measures (9YO, r = 0.43-0.46, P < 0.001; 15YO, r = 0.30-0.37, P < 0.003) and fitness (9YO, r = −0.29, P = 0.003; 15YO, r = −0.32, P = 0.001). Adjustment for fitness did not affect the relations between fatness and fasting insulin in 9YO (r = 0.33-0.37, P < 0.001); however, only waistadj remained significantly related to fasting insulin (r = 0.24, P = 0.016) in 15YO. Children in the upper half of fitness and fatness split on the median did not differ in fasting insulin from children in the upper half of fitness but lower half of fatness. Fatness was related to fasting insulin in 9YO (r = 0.51-0.54, P = 0.001) and 15YO (r = 0.31-0.35, P = 0.011-0.028) in the lower half of fitness, but no association was observed in the upper half of fitness in either group.

Conclusion: Fatness has a greater association with fasting insulin than fitness, especially among 9YO; however, fitness attenuates the adverse relation of fatness to fasting insulin in 15YO but does not change it in 9YO. In both age groups, being fitter and fatter does not result in greater fasting insulin than being fitter and leaner, and fatness is primarily associated with fasting insulin in lower-fit children.

1Center for Sport and Health Sciences, Iceland University of Education, Laugarvatn, ICELAND; 2Department of Movement Science, 3Unit for Nutrition Research, Landspitali-University Hospital and Department of Food Science and Human Nutrition, and 4Children's Hospital, Landspitali-University Hospital and Faculty of Medicine, University of Iceland, Reykjavík, ICELAND

Address for correspondence: Sigurbjörn Árni Arngrímsson, Ph.D., Center for Sport and Health Sciences, Iceland University of Education, Lindarbraut 4, 840 Laugarvatn, Ireland; E-mail:

Submitted for publication May 2007.

Accepted for publication August 2007.

© 2008 American College of Sports Medicine