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Reduced salt intake reduces blood pressure in people with or without hypertension

He F, Jiafu L, MacGregor G. Effect of longer term modest salt reduction on blood pressure: Cochrane systematic review and meta-analysis of randomised trials. BMJ. 2013;346:1325.

Review question

What is the effect of long-term salt reduction on blood pressure?

Background

Salt raises blood pressure (BP) in some people. A lower salt intake is related to a reduced risk of heart attacks and stroke.

Healthy adults need only 1,500 mg of salt per day. The maximum recommended daily intake is 2,300 mg. 1 teaspoon of salt = 2,400 mg sodium.

For most people, about 85% of salt intake is from food, with only about 15% added by salt shaker.

How the review was done

This summary is based on a systematic review of 34 randomized controlled trials of 3230 people 22 to 73 years of age. Publication period was 1973 to 2009.

• 12 trials included 2,240 people with normal BP (median BP 127/77 mg Hg). Their salt intake ranged from 7,500 to 11,700 mg/day. Study duration ranged from 1 month to about 1 year.
• 22 trials included 990 people with high BP (median BP 148/93 mm Hg). Their salt intake ranged from 7,300 to 11,200/day. Study duration ranged from about 1 month to about 3 years.

Reduced salt intake for 4 or more weeks was compared with usual salt intake.

The main outcomes were systolic and diastolic BP.

What the researchers found

For all people (high or normal BP)

• The average reduction in salt intake was 4,400 mg/day.
• For systolic BP, this reduction resulted in an average lowering of 4.18 mm Hg.
• For diastolic BP, the average lowering was 2.06 mm Hg.
• A daily reduction of salt intake of 6,000 mg was associated with a lowering of systolic BP of 5.8 mm Hg.

For people with high BP

• The average reduction in salt intake of 4,400 mg/day resulted in an average lowering of 5.39 mm Hg. for systolic BP.
• The average lowering of diastolic BP was 2.82 mm Hg.

For people with normal BP

• The average reduction in salt intake of 4,400 mg/day resulted in an average lowering of 2.42 mm Hg for systolic BP.
• The average lowering of systolic BP was 1.00 mm Hg.

Conclusion

A reduction in salt intake for 4 or more weeks reduces blood pressure in patients with or without hypertension, regardless of sex or ethnicity.