Blood Pressure Effects of Sodium Reduction
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The authors performed a search for studies that investigated the BP effects of changes in dietary sodium, and conducted a dose–response meta-analysis using the novel 1-stage cubic spline mixed-effects model. Studies were required to have at least 4 weeks of follow-up; 24-hour urinary sodium excretion measurements; sodium manipulation through dietary change or supplementation, or both; and measurements of systolic BP (sBP) and diastolic BP (dBP) at the beginning and end of treatment. For the dose–response assessment of the effect of achieved sodium intake on BP levels, 2 g/d of sodium intake was the reference value; 87 mmol/d corresponds to 2 g of sodium or 5 g of salt.

-- There were 85 eligible trials with over 10,000 participants (65 trials with hypertension, 9 a combination, and 11 without hypertension) with sodium intake ranging from 0.4-7.6 g/d and follow-up from 4 weeks to 36 months.

-- Mean study age ranged from 23-73 years. The difference in sodium excretion between intervention and control groups ranged from 0.1-7.1 g/d with a median of 1.8 g/d.

-- In linear regression analysis, every 100 mmol/d reduction in urinary sodium excretion was associated with a lower mean sBP of 5.56 mm Hg and a lower mean dBP of 2.33 mm Hg.

-- Overall, the pooled data were compatible with an approximately linear relationship between achieved sodium intake and mean sBP and dBP, with no indication of a flattening of the curve at either the lowest or highest levels of sodium exposure.

-- Results were similar for participants with or without hypertension, but the former group showed a steeper decrease in BP after sodium reduction.

-- Intervention duration (more than 12 weeks vs. 4-11 weeks), type of study design (parallel or crossover), use of antihypertensive medication, and participants’ sex had little influence on the BP effects of sodium reduction.

-- Additional analyses based on the BP effect of difference in sodium exposure between study arms at the end of the trial confirmed the results on the basis of achieved sodium intake.

Conclusively, in this dose–response analysis of sodium reduction in clinical trials, there is an approximately linear relationship between sodium intake and reduction in both sBP and dBP across the entire range of dietary sodium exposure. The effect of sodium reduction on level of BP was more pronounced in participants with a higher BP level.

The DASH diet (limited to 2300 mg of sodium or 5750 mg of salt) for hypertension has been shown to be effective in lowering BP and is strongly supported in guidelines. That there is evidence that a modest reduction in salt intake might prevent the onset of hypertension in persons with BP above normal (120/80 mm Hg), and particularly those with a family history of hypertension or metabolic risk factors, is highly encouraging.