Reduced dietary salt for the prevention of cardiovascular disease

Abstract

Background: This is an update of a Cochrane review of the effects of dietary advice, including low sodium salt substition, to reduce salt intake on mortality and cardiovascular events. Objectives: 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. Search methods: The searches of CENTRAL, MEDLINE, EMBASE and CINAHL were updated and last run in May 2013. References of included studies and reviews were also checked. No language restrictions were applied. Selection criteria: Trials fulfilled the following criteria: (1) randomised with follow up of at least six-months, (2) intervention was reduced dietary salt (through advice to reduce salt intake or low sodium salt substition), (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. Main results: Nine studies met the inclusion criteria -three in normotensives (n=3518), and six in hypertensives or mixed populations of normo-and hypertensives (n=3908) with end of trial follow-up of six 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 0.68, 95% CI: 0.37 to 1.25, 42 deaths; longest follow up RR 0.90, 95% CI: 0.58 to 1.40, 79 deaths) and hypertensives (end of trial RR 0.99, 95% CI: 0.86 to 1.15, 564 deaths; longest follow up RR 0.98, 95% CI; 0.86 to 1.13, 665 deaths) showed no strong evidence of any effect of salt reduction. There was no strong evidence of benefit in cardiovacular mortality (hypertensives: end of trial RR 0.79, 95% CI 0.54 to 1.16), or in cardiovascular morbidity in normotensives: longest follow-upRR 0.71, 95% CI: 0.42 to 1.20, 200 events;hypertensives: longest follow up RR 0.93, 95% CI 0.50 to 1.72). advice to reduce salt showed small reductions in systolic blood pressure (MD -1.04mmHg, 95% CI: -2.02 to -0.05) and diastolic blood pressure (MD -0.66mmHg, 95% CI-1.22, -0.10) in normotensives and greater reductions in systolic BP in hypertensives (MD-3.82mmHg 95% CI -5.42 to -2.22). We found no information on participants health-related quality of life. Authors' conclusions: Despite collating more event data than previous systematic reviews of randomised controlled trials (606 deaths in some 7426 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. Our estimates of benefits from advice to reduce dietary salt are consistent with the predicted small effects on clinical events attributable to the small blood pressure reduction achieved.

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Affiliated Institutions

• London School of Hygiene & Tropical Medicine GB
• University of East Anglia GB
• University of Exeter GB
• Florida Atlantic University US

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