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A Meta-analysis of Randomized Controlled Trials

Julian Paul Midgley, BM BCh; Andrew Glenday Matthew; Celia Margaret T. Greenwood, MMath; Alexander Gordon Logan, MD

JAMA. 1996;275(20):1590-1597.

Abstract
Objective.
—To ascertain whether restriction of dietary sodium lowers blood pressure in hypertensive and normotensive individuals.

Data Sources.
—An English-language computerized literature search, restricted to human studies with Medical Subject Heading terms, "hypertension," "blood pressure," "vascular resistance," "sodium and dietary," "diet and sodium restricted," "sodium chloride," "clinical trial," "randomized controlled trial," and "prospective studies," was conducted. Bibliographies of review articles and personal files were also searched.

Trial Selection.
—Trials that had randomized allocation to control 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 purposedesigned forms, and discrepancies were resolved by discussion.

Data Synthesis.
—The 56 trials that met our inclusion criteria showed significant heterogeneity. Publication bias was also evident. The mean reduction (95% confidence interval) in daily urinary sodium excretion, a proxy measure of dietary sodium intake, was 95 mmol/d (71-119 mmol/d) in 28 trials with 1131 hypertensive subjects and 125 mmol/d (95-156 mmol/d) in 28 trials with 2374 normotensive subjects. After adjustment for measurement error of urinary sodium excretion, the decrease in blood pressure 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 individuals and small and nonsignificant in trials of normotensive individuals whose meals were prepared and who lived outside the institution setting.

Conclusion.
—Dietary sodium restriction for older hypertensive individuals might be considered, but the evidence in the normotensive population does not support current recommendations for universal dietary sodium restriction.

(JAMA. 1996;275:1590-1597)

Author Affiliations
From the Division of Nephrology, Department of Medicine, University of Toronto (Ontario) (Drs Midgley and Logan), and the Henry S. Rosenberg Division of Clinical Epidemiology, Samuel Lunenfeld Research Institute, Mount Sinai Hospital, Toronto (Drs Midgley and Logan, Mr Matthew, and Ms Greenwood). Dr Midgley is now with the Division of Nephrology, Department of Paediatrics, University of Calgary (Alberta).

Footnotes
Presented in part at the American Society of Nephrology 27th annual meeting, Orlando, Fla, October 27, 1994.

Reprints: Alexander G. Logan, MD, Suite 850, Samuel Lunenfeld Research Institute, Mount Sinai Hospital, 600 University Ave, Toronto, Ontario, Canada M5G 1X5.

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