Novel measures of inflammation and insulin resistance are related to obesity and fitness in a diverse sample of 11-14 year-olds: The HEALTHY Study

Background: GlycA is a novel serum marker of systemic inflammation. There is no information on GlycA in pediatric populations, how it differs by gender or its association with body mass index (BMI) or fitness. LP-IR is a serum measure of insulin resistance which is related to changes in BMI group in adolescents, but its relationship with fitness is unknown. The current study examined the independent associations between fitness and BMI with GlycA and LP-IR among US adolescents. 
Methods: Participants were 1664 US adolescents from the HEALTHY study with complete 6^th and 8^th grade BMI, fitness and blood data. GlycA and LP-IR were measured by NMR spectroscopy. Three BMI groups and three fitness groups were created. Linear mixed models examined associations between GlycA, LP-IR, fitness and BMI.Results: LP-IR decreased between 6^th and 8^th grade. GlycA increased among girls butdecreased among boys. At 8^th grade, median GlycA values were 27 (7.6%) µmol/L higher(381 versus 354) for girls than boys. Median GlycA 6^th grade values were 9% higher in obese girls than healthy weight girls. Overall there was strong evidence (p<0.001) that GlycA was higher in higher BMI groups. Fitness was negatively associated with GlycA (r = -0.37 and -0.35) and LP-IR (r = -0.34 and – 0.18) at the 6^th and 8^th grade assessments. As BMI category increased and fitness category decreased, GlycA and LP-IR levels increased. Lowest GlycA was found in the low BMI / high fitness group.
Conclusions: GlycA was associated with BMI and fitness among in US adolescents. These findings suggest that there are independent effects for BMI and fitness group with both GlycA and LP-IR. Future studies should validate the role of GlycA and LP-IR to evaluate the effects of interventions to modify obesity and fitness in order to improve systemic inflammation and insulin resistance.