Association between cardiorespiratory fitness level and insulin resistance in adolescents with various obesity categories

ARTICLE HIGHLIGHTS

Research background

The global obesity epidemic, not sparing children and adolescents, is accompanied by rapid increase in the prevalence of cardiometabolic disorders. The association between obesity and insulin resistance is well established, along with the fact that insulin resistance represents a pivotal step in the progression towards prediabetes and type 2 diabetes. Obese adolescents who are in puberty should be regarded as a particularly vulnerable group for glucose metabolism dysregulation. Growing evidence supports the notion that young-onset type 2 diabetes has a more aggressive disease phenotype, leading to early development of complications, and adversely affecting quality of life and long-term outcomes. As more than half of the world’s population is expected to be overweight or obese within the next decade, expanding the options to manage adolescent obesity is essential to treat the epidemic.

Research motivation

Cardiorespiratory fitness (CRF), referring to ability of the circulatory and respiratory systems to supply oxygen to skeletal muscle mitochondria for energy production during sustained physical activity has been associated with the insulin resistance, irrespective of body weight. In children and adolescents, CRF is an important marker of health which shows an inverse relationship with obesity, insulin resistance and cardiometabolic risk. Available data confirm that association between fatness and cardiometabolic risk scores could be partially decreased with improvements in fitness levels. It seems that early intervention and prevention strategies targeting youth CRF may be associated with reduced risk for obesity and cardiometabolic disease later in life.

Research objectives

To investigate the association between CRF and insulin resistance in obese adolescents, with special emphasis on severely obese adolescents.

Research methods

This was a prospective, cross-sectional study including 200 pubertal adolescents, 10 years to 18 years of age. According to body mass index (BMI), adolescents were classified as mildly obese (BMI 100% to 120% of the 95^th percentile for age and sex) or severely obese (BMI ≥ 120% of the 95^th percentile for age and sex or ≥ 35 kg/m², whichever was lower). Participant body composition was assessed by bioelectrical impedance analysis (BIA). A homeostatic model assessment of insulin resistance (HOMA-IR) was calculated. Maximal oxygen uptake (VO₂max) was determined from submaximal treadmill exercise test. CRF was expressed as VO₂max scaled by total body weight (mL/min/kg TBW) or by fat free mass (mL/min/kg FFM), and then categorized as poor, intermediate or good, according to VO₂max terciles. Data were analyzed by statistical software package SPSS (IBM SPSS Statistics for Windows, Version 24.0). P value < 0.05 was considered statistically significant.

Research results

We observed a weak negative correlation between CRF and HOMA-IR [Spearman’s rank correlation coefficient (r_s) = -0.28, P < 0.01 for CRF_TBW; (r_s) =-0.21, P < 0.01 for CRF_FFM]. A one-way analysis of variance (ANOVA) revealed a significant main effect of CRF on HOMA-IR [F₍₂₂₀₀₎ = 6.840, P = 0.001 for CRF_TBW; F₍₂₂₀₀₎ = 3.883, P = 0.022 for CRF_FFM]. Subsequent analyses showed that obese adolescents with poor CRF had higher HOMA-IR than obese adolescents with good CRF (P = 0.001 for CRF_TBW; P = 0.018 for CRF_FFM). Two-way ANOVA with Bonferroni correction confirmed significant effect of interaction of CRF level and obesity category on HOMA-IR [F₍₂₂₀₀₎ = 3.292, P = 0.039 for CRF_TBW]. Severely obese adolescents had higher HOMA-IR than mildly obese, with either good or poor CRF. However, HOMA-IR did not differ between severely obese adolescents with good and mildly obese adolescents with poor CRF.

Research conclusions

CRF is important determinant of insulin resistance in obese adolescents, regardless of obesity category. Therefore, CRF assessment should be a part of diagnostic procedure, and its’ improvement should be a therapeutic goal.

Research perspectives

Large scale prospective studies are needed to expand the knowledge of CRF, IR, and cardiometabolic health. Also, determination of participants’ body composition by using different methods (such as abdominal MR scans) would offer more precise insight into type and distribution of body fat.