Low heart rate variability and sympathetic dominance modifies the association between insulin resistance and metabolic syndrome: ― The Toon Health Study ―

Background: Insulin resistance is strongly associated with metabolic syndrome (MetS), but it is not known how this association is influenced by the autonomic nervous system, which controls insulin secretion. Methods and Results: The subjects were 2,016 individuals aged 30-79 years enrolled between 2009 and 2012. MetS was determined using the harmonized MetS definition, which includes waist circumference, blood pressure, triglycerides, high-density lipoprotein cholesterol, and fasting glucose. The homeostasis model assessment index for insulin resistance (HOMA-IR) and Gutt’s insulin sensitivity index (ISI) were calculated based on fasting and 2 h-post-load glucose and insulin concentrations in a 75-g oral glucose tolerance test. The 5-min heart rate variability (HRV) was evaluated using time-domain indices of standard deviations of NN intervals (SDNN) and root mean square of successive differences (RMSSD). Power spectral analysis yielded frequency-domain measures for HRV: high-frequency (HF) power, low-frequency (LF) power and LF/HF. Multivariable adjusted logistic models showed that the highest quartiles for SDNN, RMSSD, LF, and HF vs. the lowest quartiles had a significant association with MetS. RMSSD, HF, and LF/HF remained significantly associated with MetS after adjustment for HOMA-IR (or ISI). Additive interactions between the levels of high LF/HF and high HOMA-IR (or low ISI) were significantly positive. Conclusions: Sympathovagal imbalance as evidenced by low HF and high LF/HF modified the association of insulin resistance or low insulin sensitivity with MetS.