Modest salt intake reduction for 4 weeks or longer decreases blood pressure

Abstract

Commentary on: He FJ, Li J, Macgregor GA. Effect of longer-term modest salt reduction on blood pressure. Cochrane Database Syst Rev 2013;4:CD004937 Implications for practice and research ▪ Salt restriction (<6 g/day) improves blood pressure (BP).▪ The effect in hypertensives is more significant than normotensives.▪ Small increase in renin-angiotensin-aldosterone (RAAS) markers.▪ Long-term data regarding the effects of sodium restriction is limited. ContextHypertension is a primary cause of death and disability. 1 Despite great strides in achieving BP targets, the majority of patients remain undertreated. Current recommendations include the dietary approaches to stop hypertension (DASH) diet and sodium reduction (6 g/day salt). 1 DASH-sodium is the sequel to the DASH study, as salt was not a factor originally. 2 Reductions in the BP by decreasing salt, while not as impressive as with DASH, were still substantial. A reduction of 4 g/day of salt for 30 days had similar effects to single drug therapy. Two recent meta-analyses have shown dissimilar long-term sodium reduction effects. 3 MethodsStudies were included if they were randomised, included participants aged 18 and above, had sodium restriction as a solo intervention and lasted more than 4 weeks. 4 The data were gathered by an inverse variance method in a random-effects meta-analysis. The heterogeneity was determined by I 2 (I 2 >50% important). I 2 describes the percentage of total variation across studies due to heterogeneity rather than chance. A I 2 close to 0% means there is consistency in the results of the studies included in the meta-analysis, A I 2 =50% means that half of the total variability is caused by true heterogeneity between studies. Sources of heterogeneity were evaluated by metaregression analyses and weighted by the inverse variance of changes in BPs. The researchers also evaluated change in 24 h urinary sodium and BP. Funnel plot asymmetry was used to detect potential publication bias and Egger's regression test to measure funnel plot asymmetry. FindingsThe meta-analysis included 34 studies (n=3230). The salt reduction intake by 4.4 g/day resulted in a -4.18 mm Hg change in systolic BP (SBP) and -2.06 mm Hg diastolic BP. Changes in 24 h urinary sodium, age, BP and ethnicity were all significantly associated with SBP changes. Hypertensives (vs normotensives) and black patients (vs white patients) had greater BP reduction. A 1-year increase in age was associated with a 0.06 mm Hg greater decrease in SBP with salt reduction.There was a statistically significant increase in plasma renin activity, aldosterone and norepinephrine. There was no change in cholesterol, however, <25% of trials measured low-density lipoprotein, high-density lipoprotein, triglycerides and total cholesterol CommentaryThe role of dietary sodium in health and disease has been a topic of debate for many decades. 4 The meta-analysis shows that a modest reduction in salt intake (5-9.4 g/day) reduces BP in hypertensives and normotensives. Small individual BP changes can have a...