Relationships between physical activity and plasma leptin levels in healthy children: the Fleurbaix-Laventie Ville Sante II Study

OBJECTIVE: To study the relationships between physical activity and plasma leptin levels in children from a population-based study, taking into account puberty stages. DESIGN: Subjects were part of the Fleurbaix-Laventie Ville Sante (FLVS) II Study, a longitudinal study on the determinants of weight gain in children and their parents. At baseline examination, 253 girls and 257 boys aged 8-18 y were examined. MEASUREMENTS: Height and weight were measured, adiposity was assessed by the sum of four skinfold thicknesses (SSK). Pubertal stage was assigned according to Tanner. Leisure-time physical activity (LTPA) was assessed by the Modifiable Activity Questionnaire and ambulatory activity by pedometer recording over a week. A fasting blood sample was obtained to determine plasma leptin and insulin levels. RESULTS: Plasma leptin was higher in girls compared to boys (8.3 (1.6-36.5) ng/ml vs 2.2 (0.1-15.3) ng/ml, P<0.001). Multivariate analyses were performed with leptin as dependent variable, and number of steps by day, Tanner stage, insulin and SSK as independent variables. In girls, leptin was negatively correlated to number of steps/day (P<0.001) and positively to SSK (P<0.001) and insulinemia (P<0.001). In boys, leptin was correlated to insulinemia (P<0.001), SSK (P<0.001), Tanner stage (P<.0001), but not to physical activity. CONCLUSION: Physical activity is negatively related to leptin levels in girls only and this association is independent of fasting plasma insulin. In children, fasting insulinemia remains associated with leptin levels after taking into account adiposity, physical activity and Tanner stage.