Effect of longer-term modest salt reduction on blood pressure

He FJ, MacGregor GA

Published Online:

October 8, 2008

Current public health recommendations in most developed countries are to reduce salt intake by about half, i.e. from approximately 10 grams per day to 5 grams per day. Our pooled analysis of randomised trials of 4 weeks or more in duration showed that reduction in salt intake lowers blood pressure both in individuals with elevated blood pressure and in those with normal blood pressure. These results support other evidence for a modest and long term reduction in population salt intake. If this occured it would result in a lower population blood pressure, and a reduction in strokes, heart attacks and heart failure. Furthermore, our study is consistent with the fact that the lower the salt intake, the lower the blood pressure. The current recommendations to reduce salt intake to 5 grams per day will lower blood pressure, but a further reduction to 3 grams per day will lower blood pressure more.

Abstract (click to read)

Background:

Many randomised trials assessing the effect of salt reduction on blood pressure show reduction in blood pressure in individuals with high blood pressure. However, there is controversy about the magnitude and the clinical significance of the fall in blood pressure in individuals with normal blood pressure. Several meta-analyses of randomised salt reduction trials have been published in the last few years. However, most of these included trials of very short duration (e.g. 5 days) and included trials with salt loading followed by salt deprivation (e.g. from 20 to 1 g/day) over only a few days. These short-term experiments are not appropriate to inform public health policy which is for a modest reduction in salt intake over a prolonged period of time. A meta-analysis (Hooper 2002) is an important attempt to look at whether advice to achieve a long-term salt reduction (i.e. more than 6 months) in randomised trials causes a fall in blood pressure. However, most trials included in this meta-analysis achieved a small reduction in salt intake; on average, salt intake was reduced by 2 g/day. It is, therefore, not surprising that this analysis showed a small fall in blood pressure, and that a dose-response to salt reduction was not demonstrable.

Objectives:

To assess the effect of the currently recommended modest salt reduction on blood pressure in individuals with elevated and normal blood pressure.
To assess whether there is a dose-response to salt reduction.

Search strategy:

We searched MEDLINE, EMBASE, Cochrane library and reference list of original and review articles.

Selection criteria:

We included randomised trials with a modest reduction in salt intake and duration of 4 or more weeks.

Data collection and analysis:

Data were extracted independently by two persons. Mean effect sizes were calculated using both fixed and random effects model. Weighted linear regression was performed to examine the relationship between the change in urinary sodium and the change in blood pressure.

Main results:

Twenty trials in individuals with elevated blood pressure (n=802) and 11 trials in individuals with normal blood pressure (n=2220) were included. In individuals with elevated blood pressure the median reduction in urinary sodium was 78 mmol/24h (4.6 g/day of salt), the mean reduction in blood pressure was -5.06 mmHg (95%CI:-5.81 to -4.31) for systolic and -2.70 mmHg (95% CI:-3.16 to -2.24) for diastolic. In individuals with normal blood pressure the median reduction in urinary sodium was 74 mmol/24h (4.4 g/day of salt), the mean reduction in blood pressure was -2.03 mmHg (95% CI: -2.56 to -1.50) for systolic and -0.99 mmHg (-1.40 to -0.57) for diastolic. Weighted linear regression showed a significant relationship between the reduction in urinary sodium and the reduction in blood pressure.

Authors' conclusions:

Our meta-analysis demonstrates that a modest reduction in salt intake for a duration of 4 or more weeks has a significant and, from a population viewpoint, important effect on blood pressure in both individuals with normal and elevated blood pressure. These results support other evidence suggesting that a modest and long-term reduction in population salt intake could reduce strokes, heart attacks, and heart failure. Furthermore, our meta-analysis demonstrates a correlation between the magnitude of salt reduction and the magnitude of blood pressure reduction. Within the daily intake range of 3 to 12 g/day, the lower the salt intake achieved, the lower the blood pressure.

This record should be cited as:

He FJ, MacGregor GA. Effect of longer-term modest salt reduction on blood pressure. Cochrane Database of Systematic Reviews 2004, Issue 3. Art. No.: CD004937. DOI: 10.1002/14651858.CD004937

Assessed as up to date:

May 9, 2005

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Primary Review Group:

Hypertension Group

Health topics:

Heart & circulation > Hypertension > Prevention

Heart & circulation > Hypertension > Treatment: non-pharmacological

Kidney disease > Hypertension > Prevention

Kidney disease > Hypertension > Treatment: non-pharmacological

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Effect of longer-term modest salt reduction on blood pressure

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