Fifty-six RCTs (n=3,505) in 53 articles: 28 RCTs included hypertensive participants (n=1,131), while the remaining 28 RCTs examined normotensive participants (n=2,374).
The dietary intervention effect averaged 95 mmol/day (range: 71 to 119) in the 28 hypertensive trials and 125 mmol/day (range: 95 to 156) in the 28 normotensive trials. There was significant heterogeneity among trials in the effect of dietary sodium restriction on blood-pressure; this heterogeneity was not eliminated when taking study design and quality into account.
After adjustment for measurement error in urinary sodium excretion, regression analysis showed a decrease in blood-pressure of 3.7 mmHg (range: 2.35 to 5.05) for systolic (p<0.001) and 0.9 mmHg (range: -0.13 to 1.85) for diastolic (p=0.09), for a 100 mmol/day reduction in daily sodium excretion, in the hypertensive trials. For the same reduction in daily sodium excretion, the normotensive trials showed decreases of 1.0 mmHg (range: 0.51 to 1.56; p<0.001) and 0.1 mmHg (range: -0.32 to 0.51; p=0.64) in systolic and diastolic blood-pressure, respectively.
A statistically-significant intercept, representing a decrease in blood-pressure with no change in dietary sodium intake, was observed in the hypertensive trials for both systolic and diastolic blood-pressure.
Subgroup analysis demonstrated large decreases in blood-pressure in the trials of older hypertensive individuals. In the 14 trials of normotensive non-institutionalised patients whose meals were prepared for them, there was no evidence of a significant change in blood-pressure.
Publication bias was examined and found to be evident in favour of small trials reporting a reduction in blood-pressure.