Resting Heart Rate Variability, Inflammation, and Insulin Resistance in Overweight and Obese Adolescents

The prevalence of obesity is increasing in young people in the United States. Lately, low-grade inflammation is recognized as accompanying obesity, a known risk factor for type 2 diabetes. Autonomic dysfunction is a prominent feature of adult diabetes, but its prevalence in adolescents in prediabetic states or with diabetes risk factors is unknown. We undertook to study obesity, inflammation, insulin resistance, and autonomic dysfunction together in a population of adolescents aged 13-18 years.

Subjects gave a blood sample for cytokine analysis and a 5-min resting EKG for analysis of resting heart rate variability. TNF-α, IL-6, c-reactive protein (CRP), MCP-1, and IL-10 were analyzed by enzyme-linked immunosorbent assay, and Fourier Transform was applied to electrocardiographic recordings of R-R intervals for analysis in frequency space. The HOMA calculation was used as an index of insulin sensitivity.

TNF-α, IL-6, CRP, MCP-1, HOMA, and insulin levels, but not serum glucose or IL-10, were higher in the obese subjects. Low-frequency (0.04-0.15 Hz) and high-frequency (0.15-0.4 Hz) fluctuations of R-R intervals were lower in the obese subjects, but the normalized low-frequency power was not different, suggesting proportional reduction in variability in both ranges and impairment of both sympathetic and parasympathetic systems.

Chronic low-grade inflammation, insulin resistance, and autonomic dysfunction are present at an early age in obese youths; early detection of inflammation may facilitate meaningful lifestyle changes in this high-risk group.