Effect of low-sodium salt substitutes on blood pressure, detected hypertension, stroke and mortality: A systematic review and meta-analysis of randomised controlled trials

Objective A systematic review and meta-analysis was conducted to assess the efficacy of low-sodium salt substitutes (LSSS) as a potential intervention to reduce cardiovascular (CV) diseases. Methods Five engines and ClinicalTrials.gov were searched from inception to May 2018. Randomised controlled trials (RCTs) enrolling adult hypertensive or general populations that compared detected hypertension, systolic blood pressure (SBP), diastolic blood pressure (DBP), overall mortality, stroke and other CV risk factors in those receiving LSSS versus regular salt were included. Effects were expressed as risk ratios or mean differences (MD) and their 95% CIs. Quality of evidence assessment followed GRADE (Grading of Recommendations Assessment, Development and Evaluation) methodology. Results 21 RCTs (15 in hypertensive (n=2016), 2 in normotensive (n=163) and 4 in mixed populations (n=5224)) were evaluated. LSSS formulations were heterogeneous. Effects were similar across hypertensive, normotensive and mixed populations. LSSS decreased SBP (MD -7.81 mm Hg, 95% CI -9.47 to -6.15, p<0.00001) and DBP (MD -3.96 mm Hg, 95% CI -5.17 to -2.74, p<0.00001) compared with control. Significant increases in urinary potassium (MD 11.46 mmol/day, 95% CI 8.36 to 14.55, p<0.00001) and calcium excretion (MD 2.39 mmol/day, 95% CI 0.52 to 4.26, p=0.01) and decreases in urinary sodium excretion (MD -35.82 mmol/day, 95% CI -57.35 to -14.29, p=0.001) were observed. Differences in detected hypertension, overall mortality, total cholesterol, triglycerides, glucose or BMI were not significant. Quality of evidence was low to very low for most of outcomes. Conclusions LSSS significantly decreased SBP and DBP. There was no effect for detected hypertension, overall mortality and intermediate outcomes. Large, long-term RCTs are necessary to clarify salt substitute effects on clinical outcomes.