Discrepant acute effect of saline loading on blood pressure, urinary sodium and potassium according to salt intake level: EpiSS study

Acute dietary salt intake may cause an elevation in blood pressure (BP). The study aimed to assess the acute effect of saline loading on BP in subjects with different levels of salt intake. This study is based on the baseline survey of systemic epidemiology of salt sensitivity study. The sodium excretion in the 24-hour urine was calculated for estimating the level of salt intake. Subjects were performed an acute oral saline loading test (1 L), and data of 2019 participants were included for analyses. Multivariate linear regression and stratified analyses were performed to identify associations between 24-hour urinary sodium (24hUNa) with BP changes. Due to saline loading, systolic BP (SBP), pulse pressure, and urinary sodium concentration were significantly increased, while diastolic BP, heart rate, and urinary potassium concentration were significantly decreased. The SBP increments were more significant in subjects with lower salt intake, normotensives, elders, males, smokers, and drinkers. There was a significant linear negative dose-response association between SBP increment with 24hUNa (beta = -0.901, 95% CI: -1.253, -0.548), especially in lower salt intake individuals (beta = -1.297, 95% CI: -2.338, -0.205) and hypertensive patients (beta = -1.502, 95% CI: -2.037, -0.967). After excluding patients who received antidiabetic or antihypertensive medicines, the effects of negative associations weakened but remained significantly. In conclusion, acute salt loading leads to an increment in SBP, and the increased SBP was negatively related with 24hUNa. This study indicated avoiding acute salt loading was important for escaping acute BP changes, especially in lower salt intake populations.