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Salt intake: the lower the better

 

Clinical bottom line

Reducing salt intake by 3 g per day lowers blood pressure, but the effect is doubled with a 6 g per day reduction and tripled with a 9 g per day reduction.


Background

Too much salt can cause high blood pressure, which in turn is one of the most important risk factors for cardiovascular disease. The average salt intake in the UK is between 9 and 12 g per day. Current recommendations are to reduce salt intake to 6 g per day or less. This paper asks whether these recommendations are low enough and whether further reductions in salt intake would have greater effects on blood pressure (i.e. whether there is a dose-response to salt reduction).

Reference

FJ He, A MacGregor. How far should salt intake be reduced? Hypertension 2003 42: 1093-1099.

Systematic review

This paper re-analysed a meta-analysis. To be included, studies had to meet the following criteria:

Results


Hypertensive trials

Hypertensive trials

Blood pressure results

Hypertensives
A reduced salt intake of:
Predicted a fall in systolic and diastolic blood pressure of:
50 mmol or 3 g/d
3.6/1.9 mmHg
100 mmol or 6 g/d
7.1/3.9 mmHg
150 mmol or 9 g/d
10.7/5.8 mmHg

 

Normotensives
A reduced salt intake of:
Predicted a fall in systolic and diastolic blood pressure of:
50 mmol or 3 g/d
1.8/0.8 mmHg
100 mmol or 6 g/d
3.6/1.7 mmHg
150 mmol or 9 g/d
5.4/2.5 mmHg

The impact on cardiovascular disease

The impact of reducing salt intake on cardiovascular disease was estimated using falls in blood pressure from both hypertensives and normotensives. The results are shown in Table 1, where SBP = systolic blood pressure; DBP = diastolic blood pressure; and IHD = ischaemic heart disease.

Table 1. Predicted reductions in stroke and ischaemic heart disease deaths\

Measure
Reduction in salt intake
3 g/d
6 g/d
9 g/d
SBP
DBP
SBP
DBP
SBP
DBP
Fall in BP in all participants
2.5
1.4
5
2.8
7.5
4.2
Reduction in stroke death, %
12
14
23
25
32
36
Stroke deaths prevented in UK
7,300
8,300
13,700
15,500
19,300
21,600
Reduction in IHD, %
9
10
16
19
23
27
IHD deaths prevented in UK
10,600
12,400
20,300
23,600
29,100
33,700

 

Comment

It was estimated that a reduction of 3 g/d in salt intake would lower blood pressure by 2.5/1.4 mmHg, which would reduce strokes by 12 to 14% and ischaemic heart disease by 9% to 10%. In the UK, the total number of stroke deaths is 60,666 per year and the total number of ischaemic heart disease deaths is 124,037 per year. Therefore, a reduction of 3 g/d in salt intake would prevent approximately 7,300 to 8,300 stroke deaths and 10,600 to 12,400 ischaemic heart disease deaths in the UK per year. These effects are predicted to double with a 6 g/d reduction and triple with a 9 g/d reduction.

It was also estimated that even in normotensives, reducing salt intake by 3 g/d would lower blood pressure by 1.8/0.8 mmHg, which would reduce strokes by 9% and ischaemic heart disease by 6%. A reduction of 6 g/d would reduce strokes by 17% and ischaemic heart disease by 12% and a 9 g/d reduction would reduce strokes and ischaemic heart disease by 24% and 18% respectively.

How do we eat less salt?