Impact of Dietary Sodium Intake on Urinary Sodium Excretion in Healthy Volunteers

Abstract

Sodium homeostasis, including renal sodium excretion, plays a crucial role in the occurrence of congestion in patients with heart failure. 1 In recent years, urinary sodium concentration has emerged as a valuable biomarker, particularly in the context of acute heart failure while titrating diuretic therapy to achieve a good diuretic response. 2 Additionally, in chronic heart failure, there is evidence that urinary sodium levels can aid in risk stratification and help to predict episodes of fluid overload. 3 Nevertheless, the exact impact of dietary sodium changes on urinary sodium excretion is not yet fully understood, even in healthy people. Scientific data have challenged the traditional assumption that urinary sodium excretion directly mirrors dietary intake. 4,5 Some evidence suggests that sodium may be buffered in tissues, such as bone and soft tissues, 6 potentially affecting urinary excretion patterns beyond a simple intake-output model. The current study aimed to further explore the impact of controlled sodium loading and restriction on urinary sodium excretion patterns in healthy volunteers. Over a 3-week period, participants adhered to a very strict and well-controlled dietary sodium regimen: a low-sodium (<2 gram, 87 mmol daily) diet during the first week, a moderate-sodium (4 gram, 174 mmol daily) diet during the second week, followed by a return to a low-sodium (<2 gram, 87 mmol daily) intake during the third week. Throughout the study, participants were advised to maintain a fluid intake of 1.5 to 2 liters daily and to fill out daily food questionnaires. Participants measured their first-void urinary sodium concentration daily using the uri-nary sodium point-of-care sensor of Horiba (LAQUAT-win). 7 In addition, at the end of each week, participants collected a 24-hour urine collection, and the sodium concentration was measured to assess total urinary sodium excretion. The primary objective was to evaluate changes in urinary sodium excretion patterns following different amounts of sodium intake. The combination of spot measurements and 24-hour collections provided complementary information. First-void measurements were included as a simple and emerging tool in heart failure management , though influenced by urine dilution, whereas 24-hour collections are more burdensome but provide a complete estimate of sodium intake. The study was approved by the local ethical committee, and all participants provided written informed consent. Normality of continuous data was assessed using a Shapiro-Wilk test. Variables are summarized as means with standard deviations, medians with 25thÀ75th percentile, or numbers with percentages. Normal distributed dependent data were analyzed using the paired t-test, and nonnormally distributed continuous data were analyzed using the Wilcoxon signed-rank test for paired samples. No adjustments for multiplicity were performed. All the hypothesis testing was 2-sided with a significance level of a = 0.05. All statistical analyses were done using SPSS version 29 (IBM SPSS Inc., Chicago, IL, USA). A total of 15 healthy volunteers were included in the study; the sample size was determined based on feasibility considerations. Exclusion criteria were a history of heart failure, an estimated glomerular filtration rate (eGFR) <50ml/min/1.73m 2 , and hypertension. Median age of the participants was 32.0 (23.0À59.0) years old, with 6 (40%) men and a median body mass index of 21.4 (19.5À24.7). The systolic and diastolic blood pressures were 120 § 15 From the