Adipocytokines, body composition, and fitness in children

Recent evidence suggests a role for adipose derived cytokines (adipocytokines) such as tumor necrosis factor-alpha (TNF-alpha), IL-6, and the recently discovered adiponectin in the mechanism of impaired glucose regulation and atherosclerosis in adults. However, the relationship between adipocytokines and body composition, fasting insulin, and fitness is virtually unknown children. Fasting blood sampling was performed in 30 healthy, predominately Hispanic- and Asian-American children (16 boys, mean age 12.7 +/- 0.1 y old) from a lower socioeconomic area in Los Angeles. Adiposity was measured by dual x-ray absorptiometry (DEXA); and peak oxygen uptake using cycle ergometry. Adiponectin (mean 10.8 +/- 0.8 mug/mL) was inversely correlated with body mass index (BMI, as percentile by age) (r = -0.48, p = 0.011) and fat mass (r = -0.43, p = 0.03). In contrast, TNF-alpha and IL-6 were both positively correlated with BMI and fat mass. Adiponectin was inversely correlated with fasting insulin (r = -0.52, p = 0.006), but no correlations were found for insulin and either TNF-alpha or IL-6. Adiponectin was correlated with HDL (r = 0.448, p = 0.019). Paradoxically, peak oxygen consumption (an indicator of fitness) was negatively correlated with adiponectin levels (r = -0.471, p = 0.013) and positively correlated with TNF-alpha (r = 0.560, p = 0.002). In children, adipocytokines are correlated with fat mass, insulin sensitivity, and cardiovascular risk factors in a manner that is qualitatively similar to relationships recently observed in adults. In more obese children, the mass of fat tissue may attenuate potentially positive effects of fitness on circulating levels of adiponectin and TNF-alpha. The novel data on adiponectin suggest that deleterious dysregulation of adipocytokines associated with obesity may occur relatively early in life.