Weight, Adiposity, and Physical Activity as Determinants of an Insulin Sensitivity Index in Pima Indian Children

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Abstract
OBJECTIVE—To determine whether measures of physical activity are related to an insulin sensitivity index ([ISI] 104/fasting insulin × glucose) independent of weight or adiposity in children. RESEARCH DESIGN AND METHODS—We conducted a longitudinal study of 90 Pima Indian children (39 boys and 51 girls) at 5 and 10 years of age measuring adiposity (dual-energy X-ray absorptiometry), physical activity behavior (questionnaire: number of activities per week [ACT], average hours per week [TIME]), and energy expenditure (doubly labeled water: physical activity level [PAL]). RESULTS—In cross-sectional analyses, ACT was correlated with ISI at 5 years of age (r = 0.24, P = 0.02) and at 10 years of age (r = 0.21, P = 0.05), but these relationships were not independent of weight or adiposity. PAL was correlated with ISI at 10 years of age (r = 0.39, P = 0.03) but was not independent of weight or adiposity. Longitudinally, ISI decreased from 5 to 10 years of age, and increases in weight and adiposity were associated with decreases in ISI (r = −0.51 and −0.41, respectively; both P < 0.0001). ACT decreased from 5 to 10 years of age, but children who had smaller decreases in ACT had smaller decreases in ISI, independent of increases in weight or adiposity (partial r = 0.22, P = 0.04 adjusted for either weight or adiposity). CONCLUSIONS—These data suggest that early establishment and maintenance of an active lifestyle can have a beneficial effect on ISI that is partially independent of changes in weight or adiposity. This is particularly relevant considering the current epidemics of both obesity and type 2 diabetes in children.