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Objective: The effect of salt restriction on blood pressure is under intense debate. We tested the effect of 100 mmol salt reduction on ambulatory blood pressure (ABP) in 46 Swedish individuals, 39 of whom completed the study, using a double-blind, placebo-controlled, cross-over design. Furthermore, we tested whether the basal plasma concentration of renin or N-terminal atrial natriuretic peptide (Nt-proANP) predict the degree of salt sensitivity.

Methods: Participants received all meals and drinks with a total daily NaCl content of 50 mmol during 8 weeks. In addition, NaCl capsules (100 mmol/day) and corresponding placebo capsules were administered for 4 weeks each in random order. ABP after high-salt intake (150 mmol/day) was compared with ABP after low-salt intake (50 mmol/day). Salt sensitivity was defined as the difference between 24-h systolic ABP at the high-salt versus the low-salt periods. Baseline renin and Nt-proANP were related to salt sensitivity.

Results: Lowering of salt intake from 150 to 50 mmol/day induced significant blood pressure reductions (mean reduction, 95% confidence interval) in systolic and diastolic 24-h ABP (5.8, 3.4-8.2 and 2.6, 0.91-4.4 mmHg), daytime ABP (5.5, 2.9-8.1 and 2.3, 0.42-4.1 mmHg) and night-time ABP (6.4, 3.5-9.3 and 3.4, 1.4-5.5 mmHg). Baseline ln(renin) correlated inversely with salt sensitivity (r = -0.50, P = 0.001) whereas baseline ln(Nt-proANP) correlated directly (r = 0.33, P = 0.04).

Conclusion: Lowering of salt intake with 100 mmol/day induces clinically relevant ABP reductions. Renin and Nt-proANP, measured with individuals on their habitual diet, could be useful biomarkers to identify individuals with the greatest blood pressure-lowering benefit from reduced salt intake.

(C) 2007 Lippincott Williams & Wilkins, Inc.