Evaluation of Endothelial Function and Sympathetic Nervous Activity along the Glucose Continuum in Individuals with Habitual Low Sodium Intake

Objective: To assess endothelial function and sympathetic nervous activity in individuals with low sodium intake along the glucose continuum.

Research Designs and Methods: In this prospective observational study, participants (n=54) with low sodium intake (single 24hour urine sodium excretion <150mmol/24h) were recruited and categorized based on an oral glucose tolerance test as: controls (n=10), with impaired glucose tolerance (IGT) (n=15) and with untreated (n=12) type 2 diabetes and were then compared to individuals with treated type 2 diabetes (n=17) with established cardio-metabolic risk factors. We assessed pulse amplitude tonometry (PAT) derived measures of endothelial function using the reactive hyperemic index and arterial stiffness using augmentation index; muscle sympathetic nerve activity (MSNA) using microneurography; cardiac baroreflex; heart rate; blood pressure; fasting glucose; glycosylated hemoglobin A1c (HbA1c) and lipid profile.

Results: The mean (SD) sodium excretion was 110.6 (26) mmol/24hour. Compared to individuals from the other groups, the treated type 2 diabetes group had a lower PAT ratio (p=0.04), lower baroreflex (p=0.0002) and higher heart rate (p=0.02) suggestive of sympatho-vascular dysfunction. This occurred despite lower MSNA (p=0.005) and appropriate glycemic (mean +/-SD): HbA1c 7.2 (1.72)% (55mmol/mol), total cholesterol 4.2 (1.0) mmol/L, LDL 2.2 (1.0) mmol/L) and blood pressure (mean +/-SD) 136 (13) systolic and 78 (12) diastolic pressure (mmHg) control.

Conclusion: In individuals with treated type 2 diabetes, despite a low sodium intake and appropriately managed cardio-metabolic risk factors, endothelial and baroreflex function were impaired. Whether sodium restriction may be associated with an attenuated sympatho-vascular response in individuals with diabetes requires further investigations.