EFFECT OF REDUCED DIETARY-SODIUM ON BLOOD-PRESSURE - A METAANALYSIS OF RANDOMIZED CONTROLLED TRIALS

Objective.-To ascertain whether restriction of dietary sodium lowers b lood pressure in hypertensive and normotensive individuals. Data Sourc es.-An English-language computerized literature search, restricted to human studies with Medical Subject Heading terms, ''hypertension,'' '' blood pressure,'' ''vascular resistance,'' ''sodium and dietary,'' ''d iet and sodium restricted, ''sodium chloride,'' ''clinical trial,'' '' randomized controlled trial,'' and ''prospective studies,'' was conduc ted. Bibliographies of review articles and personal files were also se arched. Trial Selection.-Trials that had randomized allocation to cont rol and dietary sodium intervention groups, monitored by timed sodium excretion, with outcome measures of both systolic and diastolic blood pressure were selected by blinded review of the methods section. Data Extraction.-Two observers extracted data independently, using purpose- designed forms, and discrepancies were resolved by discussion. Data Sy nthesis.-The 56 trials that met our inclusion criteria showed signific ant heterogeneity. Publication bias was also evident. The mean reducti on (95% confidence interval) in daily urinary sodium excretion, a prox y measure of dietary sodium intake, was 95 mmol/d (71-119 mmol/d) in 2 8 trials with 1131 hypertensive subjects and 125 mmol/d (95-156 mmol/d ) in 28 trials with 2374 normotensive subjects. After adjustment for m easurement error of urinary sodium excretion, the decrease in blood pr essure for a 100-mmol/d reduction in daily sodium excretion was 3.7 mm Hg (2.35-5.05 mm Hg) for systolic (P<.001) and 0.9 mm Hg (-0.13 to 1. 85 mm Hg) for diastolic (P=.09) in the hypertensive trials, and 1.0 mm Hg (0.51-1.56 mm Hg) for systolic (P<.001) and 0.1 mm Hg (-0.32 to 0. 51 mm Hg) for diastolic (P=.64) in the normotensive trials. Decreases in blood pressure were larger in trials of older hypertensive individu als and small and nonsignificant in trials of normotensive individuals whose meals were prepared and who lived outside the institution setti ng. Conclusion.-Dietary sodium restriction for older hypertensive indi viduals might be considered, but the evidence in the normotensive popu lation does not support current recommendations for universal dietary sodium restriction.