Purpose: High sodium intake is an accepted risk factor for hypertension, while low Na+ intake has also been associated with increased risk of cardiovascular events. In this cross-sectional study, we examined the association of 24-h urinary Na+ excretion with haemodynamics and volume status.
Materials and methods: Haemodynamics were recorded in 510 normotensive and never-treated hypertensive subjects using whole-body impedance cardiography and tonometric radial artery pulse wave analysis. The results were examined in sex-specific tertiles of 24-h Na+ excretion, and comparisons between normotensive and hypertensive participants were also performed. Regression analysis was used to investigate factors associated with volume status. The findings were additionally compared to 28 patients with primary aldosteronism.
Results: The mean values of 24-h urinary Na+ excretion in tertiles of the 510 participants were 94, 148 and 218 mmol, respectively. Average tertile age (43.4-44.7 years), office blood pressure and pulse wave velocity were corresponding in the tertiles. Plasma electrolytes, lipids, vitamin D metabolites, parathyroid hormone, renin activity, aldosterone, creatinine and insulin sensitivity did not differ in the tertiles. In supine laboratory recordings, there were no differences in aortic systolic and diastolic blood pressure, heart rate, cardiac output and systemic vascular resistance. Extracellular water volume was higher in the highest versus lowest tertile of Na+ excretion. In regression analysis, body surface area and 24-h Na+ excretion were independent explanatory variables for extracellular water volume. No differences in urine Na+ excretion and extracellular water volume were found between normotensive and hypertensive participants. When compared with the 510 participants, patients with primary aldosteronism had 6.0% excess in extracellular water (p = .003), and 24-h Na+ excretion was not related with extracellular water volume.
Conclusion: In the absence of mineralocorticoid excess, Na+ intake, as evaluated from 24-h Na+ excretion, predominantly influences extracellular water volume without a clear effect on blood pressure.
Keywords: Blood pressure; extracellular water volume; pulse wave analysis; sodium excretion; whole-body impedance cardiography.
We evaluated sodium intake in 510 subjects by measuring their 24-h sodium excretion to the urine and examined whether sodium intake was related with alterations in cardiovascular function and fluid balance. All participants were without blood pressure lowering medications.Blood pressure was recorded by a device that senses the radial artery pulsations form the wrist. The amount of blood pumped by the heart, the transfer of pressure waves following cardiac contractions and body fluid status were evaluated using bioimpedance, a method recording changes in body electrical resistance.For the analyses, the participants were divided into tertiles according to their 24-h sodium excretions. We also compared results between normotensive and hypertensive subjects.The 24-h sodium excretion in the tertiles corresponded to about 6 g, 9 g and 13 g of salt intake per day, respectively. There were no differences between the tertiles in age, routine laboratory analyses, blood pressure, large arterial stiffness, amount blood pumped by the heart and resistance to blood flow in the arteries. However, there was more extracellular fluid in the highest versus the lowest tertile of sodium excretion. Further statistics indicated that extracellular fluid volume in the body was mainly determined by body size, but it was also moderately influenced by sodium intake.No differences in 24-h sodium excretion and extracellular water volume were found between normotensive and hypertensive participants.In subjects not using blood pressure lowering medications, sodium intake predominantly influences the amount of extracellular fluid without a clear effect on blood pressure.