Reduced dietary salt for the prevention of cardiovascular disease
Editorial Group: Cochrane Heart Group
Published Online: 6 JUL 2011
Assessed as up-to-date: 1 APR 2009
Copyright © 2013 The Cochrane Collaboration. Published by John Wiley & Sons, Ltd.
How to Cite
Taylor RS, Ashton KE, Moxham T, Hooper L, Ebrahim S. Reduced dietary salt for the prevention of cardiovascular disease. Cochrane Database of Systematic Reviews 2011, Issue 7. Art. No.: CD009217. DOI: 10.1002/14651858.CD009217.
- Publication Status: Edited (no change to conclusions)
- Published Online: 6 JUL 2011
An earlier Cochrane review of dietary advice identified insufficient evidence to assess effects of reduced salt intake on mortality or cardiovascular events.
1. To assess the long term effects of interventions aimed at reducing dietary salt on mortality and cardiovascular morbidity.
2. To investigate whether blood pressure reduction is an explanatory factor in any effect of such dietary interventions on mortality and cardiovascular outcomes.
The Cochrane Library (CENTRAL, Health Technology Assessment (HTA) and Database of Abstracts of Reviews of Effect (DARE)), MEDLINE, EMBASE, CINAHL and PsycInfo were searched through to October 2008. References of included studies and reviews were also checked. No language restrictions were applied.
Trials fulfilled the following criteria: (1) randomised with follow up of at least six-months, (2) intervention was reduced dietary salt (restricted salt dietary intervention or advice to reduce salt intake), (3) adults, (4) mortality or cardiovascular morbidity data was available. Two reviewers independently assessed whether studies met these criteria.
Data collection and analysis
Data extraction and study validity were compiled by a single reviewer, and checked by a second. Authors were contacted where possible to obtain missing information. Events were extracted and relative risks (RRs) and 95% CIs calculated.
Seven studies (including 6,489 participants) met the inclusion criteria - three in normotensives (n=3518), two in hypertensives (n=758), one in a mixed population of normo- and hypertensives (n=1981) and one in heart failure (n=232) with end of trial follow-up of seven to 36 months and longest observational follow up (after trial end) to 12.7 yrs. Relative risks for all cause mortality in normotensives (end of trial RR 0.67, 95% CI: 0.40 to 1.12, 60 deaths; longest follow up RR 0.90, 95% CI: 0.58 to 1.40, 79 deaths) and hypertensives (end of trial RR 0.97, 95% CI: 0.83 to 1.13, 513 deaths; longest follow up RR 0.96, 95% CI; 0.83 to 1.11, 565 deaths) showed no strong evidence of any effect of salt reduction. Cardiovascular morbidity in people with normal blood pressure (longest follow-up RR 0.71, 95% CI: 0.42 to 1.20, 200 events) or raised blood pressure at baseline (end of trial RR 0.84, 95% CI: 0.57 to 1.23, 93 events) also showed no strong evidence of benefit. We found no information on participants health-related quality of life.
Despite collating more event data than previous systematic reviews of randomised controlled trials (665 deaths in some 6,250 participants), there is still insufficient power to exclude clinically important effects of reduced dietary salt on mortality or cardiovascular morbidity in normotensive or hypertensive populations. Further RCT evidence is needed to confirm whether restriction of sodium is harmful for people with heart failure. Our estimates of benefits from dietary salt restriction are consistent with the predicted small effects on clinical events attributable to the small blood pressure reduction achieved.
Plain language summary
Advice to reduce salt consumption for reducing blood pressure; insufficient evidence to confirm predicted reductions in people dying prematurely or suffering cardiovascular disease
Cardiovascular disease includes heart attacks, strokes, and the need for heart surgery and is a major cause of premature death and disability. This review set out to assess whether intensive support and encouragement to cut down on salt in foods reduced the risk of death or cardiovascular disease. This advice did reduce the amount of salt eaten which led to a small reduction in blood pressure by six months. There was not enough information to detect the expected effects on deaths and cardiovascular disease predicted by the blood pressure reductions found. There was limited evidence that dietary advice to reduce salt may increase deaths in people with heart failure. Our review does not mean that asking people to reduce salt should be stopped. People should continue to strive to do this. However, additional measures - reducing the amount of hidden salt in processed foods, for example – will make it much easier for people to stick to a lower salt diet. Further evidence of measures to cut dietary salt is needed: (1) randomised controlled trials of advice to reduce salt in individuals with heart failure assessing mortality and cardiovascular events and (2) experimental or observational studies of population based interventions to reduce salt in hypertensives or healthy individuals assessing mortality and cardiovascular events.