Impact of self-monitoring of salt intake by salt meter in hypertensive patients: a randomised controlled trial (SMAL-SALT)

Abstract Background Hypertension is one of the most common chronic medical conditions. The concerned sequelae are the cardiovascular complications. 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 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. 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. Method A randomized-controlled trial was conducted in hypertensive patients whose BP was uncontrolled (SBP ≥140 mmHg or DBP ≥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. Results A total of 100 patients were enrolled, with 90 patients who met the eligible criteria and had completed to follow-up, 45 in group A and 45 in group B. Mean age was 62.9 years and 53% were females. 11.1% were treatment-naïve, and median number of antihypertensive agents was 2. Mean baseline 24-hour urine sodium was 151.6 mmol/24h and mean baseline SBP and DBP were 152.8 and 83.4 mmHg, respectively. Baseline characteristics including age, sex, number of drugs, BP, body weight, 24-hour urine sodium, creatinine, salt sensitivity, and CAVI were similar between two groups. At 8 weeks, mean decrease in 24-hour urine sodium were 29.1 mmol/24h and −0.9 mmol/24h in group A and group B, respectively (p=0.017). Mean decrease in BP (group A vs group B) were SBP, 14.3 vs 8.4 mmHg (p=0.043), and DBP 5.7 vs 1.8 mmHg (p=0.021). The salt sensitivity was improved in both groups, more in group A (detection threshold decrement = 1.547 in group A and 0.265 in group B). There was no different between change in CAVI. All patients have more motivation to maintain low salt diet after finish the study. No adverse event was observed throughout the study. Conclusions Salt meter in conjunction with dietary education, for self-monitoring of salt intake is superior to education alone in hypertensive patients, and provided better blood pressure control. Salt meter should be considered in patients with uncontrolled hypertension. Funding Acknowledgement Type of funding source: Public hospital(s). Main funding source(s): Faculty of Medicine, Ramathibodi Hospital of Mahidol University