Is there a glycemic threshold for impaired autonomic control?

Area of Science:

• Cardiovascular Physiology
• Autonomic Nervous System Function
• Metabolic Health

Background:

• Hyperglycemia is a known predictor of cardiovascular autonomic neuropathy in diabetic patients.
• The specific glucose threshold for impaired autonomic control remains unevaluated.
• Understanding early markers of autonomic dysfunction is crucial for preventative strategies.

Purpose of the Study:

• To investigate the association between fasting plasma glucose (FPG) and fasting plasma insulin (FPI) with baroreflex sensitivity (BRS) in healthy volunteers.
• To determine if FPG or FPI is a more significant predictor of reduced autonomic control.
• To establish potential glucose or insulin thresholds associated with impaired autonomic function.

Main Methods:

• 162 healthy volunteers (25-44 years) underwent measurements of FPG and FPI after an overnight fast.
• Baroreflex sensitivity (BRS) was assessed using power spectral analysis.
• Statistical analyses included univariate correlations and covariate-adjusted models.

Main Results:

• Univariate analysis revealed a negative correlation between FPG and BRS (r = -0.25, P <= 0.001).
• This association between FPG and BRS lost significance after adjusting for age, blood pressure, and BMI.
• Fasting plasma insulin (FPI) demonstrated a significant negative correlation with BRS (r = -0.32, P < 0.0001) both before and after covariate adjustment.
• Individuals in the highest quintile of FPI showed nearly a 50% reduction in BRS.

Conclusions:

• Elevated FPI is independently associated with substantial reductions in autonomic cardiac control.
• High normal FPG levels are linked to reduced autonomic control, but this appears secondary to factors like aging, obesity, and blood pressure.
• Fasting plasma insulin emerges as a stronger indicator of early autonomic dysfunction than fasting plasma glucose in healthy adults.