Impact of Self-monitoring of Salt Intake by Salt Meter in Hypertensive Patients (SMAL-SALT)

Hypertension is one of the most common chronic medical conditions. The concerned sequelae are the cardiovascular complications, especially acute myocardial infarction and stroke. In Thailand, the incidence of hypertension is increasing each year. Many clinical studies found that salt intake over the reference level (>5 g/day) would result in elevated blood pressure (BP) and long-term morbidity. Dietary salt reduction campaigns were unsuccessful, in part, due to time limitation in the clinic, lacking of awareness, and the higher threshold to detect salt taste in chronic high salt ingestion. Salt meter is a device used to detect sodium content in daily food. It will facilitate monitoring and control of salt intake. The 24-hour urinary sodium excretion is an acceptable method to reflect the quantity of sodium intake. This study aimed to compare the efficacy of salt meter plus dietary education compared with education alone in terms of salt intake reduction, blood pressure, salt taste sensitivity, and vascular consequence.

A randomized-controlled trial was conducted in hypertensive patients whose BP was uncontrolled (systolic BP ≥140 mmHg or diastolic BP ≥90 mmHg) despite therapy or antihypertensive-naïve. Patients were randomized to receive salt meter to use in conjunction with dietary education (group A) or receive education only (group B), and were followed up for 8 weeks. Dietary education was provided by certified dietician without awareness of patients' allocation. The primary endpoint was change in 24-hour urinary sodium excretion. Changes in BP, salt taste sensitivity threshold, cardio-ankle vascular index (CAVI), as well as motivation to maintain low salt diet were also analyzed.

Patients received salt-meter in conjunction with dietary education by trained dietician to help monitoring the salt content in food, as well as usual care by their primary physicians.

Salt-meter, developed by Faculty of Engineering at Mahidol University, is a device to measure sodium chloride content in the food and reflects to user with number and symbols for easy-understanding.

Using the different saline concentration in solution. Starting from the lowest to higher concentration, the point when the patient can differentiate from distilled water is called "detection threshold", and the point that patient can identify salty taste is called "recognition" threshold.

Number of patients documented to have hospitalisation for hypertension treatment including hypertensive emergency requiring intravenous antihypertensive agents.

Scale from 0 to 10 to estimate self motivation for taking low salt strategy at baseline and at 8 weeks

Inclusion Criteria: Mean SBP 140-179 mmHg or mean DBP 90-109 mmHg (average 3 times) Diagnosed of hypertension for at least 3 months No adjustment of antihypertensive agents for at least 1 month 24h Urine sodium ≥ 90 mmol/day eGFR ≥ 45 ml/min/1.73 sq.m. Exclusion Criteria: eGFR < 45 ml/min/1.73 sq.m. UACR > 300 mg/g Serum potassium > 6.0 mmol/l Serum sodium < 135 mmol/l Unable to collect 24-hour urine

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