Association Between Estimated Daily Salt Intake from Spot Urine and Nocturnal Blood Pressure in Hypertensive Patients under Antihypertensive Treatment

BACKGROUND: Excessive salt intake is a major contributor to hypertension and is associated with elevated nocturnal blood pressure (BP), particularly in the elderly and individuals with chronic kidney disease (CKD), metabolic syndrome (MetS), or diabetes, who are prone to nocturnal BP elevation in response to high salt intake. Although estimation of salt intake from spot urine is widely used, the relationship of estimated salt intake from spot urine with nighttime BP in treated patients with hypertension remains unclear. METHODS: In this cross-sectional study, we analyzed 209 hypertensive patients receiving antihypertensive therapy. Estimated daily salt intake was calculated from spot urine using a validated formula. Nighttime BP was measured over a period of seven days using a home BP monitoring device. RESULTS: The mean estimated salt intake was 9.3 ± 2.5 g/day, and the mean nighttime systolic BP was 115.6 ± 12.1 mmHg. There was no significant correlation between estimated salt intake and nighttime systolic BP (r = -0.08, P = 0.23). Multivariable linear regression analysis also showed no significant association (β=-0.070, P = 0.34). Subgroup analyses in participants aged ≥ 65 years and those with CKD, MetS, or diabetes showed no significant associations. Sensitivity analyses in participants with controlled morning BP (< 135 mmHg) and those with a ≤ 7-day interval between spot urine and nighttime BP measurements also showed no significant associations. CONCLUSIONS: Estimated salt intake from spot urine was not significantly associated with nighttime systolic BP in treated hypertensive patients, even in those prone to salt-related nocturnal BP elevation.