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Purpose of Review:
To synthesize the evidence regarding the effects of dietary sodium reduction and increased potassium intake on (and their associations with) blood pressure and risk for chronic cardiovascular diseases (CVD).
DRAFT Key Messages
- Interventions that decrease dietary sodium intake reduce blood pressure in both normotensive adults and those with hypertension. The effect of sodium reduction is greater in adults with hypertension than in those with normal blood pressure.
- Prospective cohort studies show that higher intakes of sodium are associated with greater risk for developing hypertension.
- Use of potassium-containing salt-substitutes to reduce sodium intake reduces blood pressure in adults.
- Increasing potassium intake decreases blood pressure in adults with hypertension.
- Interventions to reduce sodium intake decrease all-cause mortality slightly, but studies are inconsistent and small in number.
- Although there appears to be an association between all-cause mortality and 24-hour sodium excretion at higher sodium levels, the linearity of this relationship at lower sodium levels could not be determined.
Objectives. This systematic review synthesized the evidence regarding the effects of dietary sodium reduction and interventions to increase potassium intake on (and their associations with) blood pressure and risk for chronic cardiovascular diseases (CVD). The purpose of the review is to provide a future Dietary Reference Intakes (DRI) Committee with the evidence on chronic disease endpoints for consideration in reviewing the DRIs for sodium and potassium.
Data Sources. PubMed, EMBASE, the Cochrane Database of Systematic Reviews, Cochrane Central Register of Controlled Trials, CINAHL, Web of Science, references of prior reviews, hand searches of gray literature, and expert recommendations.
Review Methods. Two reviewers independently screened citations and full-text publications. Eligible studies included randomized controlled trials (RCTs), nonrandomized controlled trials, and prospective observational studies published to 2017 that enrolled healthy populations or those with pre-existing hypertension, CVD, diabetes, or obesity and that assessed blood pressure, incident hypertension, achievement of prespecified blood pressure goals, all-cause mortality, CVD morbidity and mortality, CHD morbidity and mortality, stroke, myocardial infarction, renal morbidity and mortality, kidney stones, and adverse events. We extracted data, assessed risk of bias, summarized and synthesized results, and evaluated strength of evidence separately for randomized controlled trials and other study designs.
Results. We identified 12,054 unique citations, of which 241 publications reporting on 159 studies were deemed eligible for the review.
Moderate-strength evidence supports a blood-pressure lowering effect of dietary sodium reduction in adults. The blood-pressure lowering effect is greater in adults with hypertension than in normotensive adults. Sodium reduction also increases the proportion of study participants who achieved a prespecified blood pressure goal in small numbers of trials (moderate SoE) but does not significantly decrease the incidence of hypertension (based on a small number of trials). Observational studies show an association between lower urinary sodium excretion and reduced risk for hypertension (low SoE because of high RoB and lack of consistency).
Only a small number of RCTs assessed the effects of sodium reduction on longer-term chronic disease outcomes: Low-strength evidence supports a small effect of sodium reduction on reducing all-cause mortality (studies were few in number and did not consistently report all-cause mortality as a primary outcome). We found no effect of sodium reduction on CVD mortality, CVD morbidity, or combined CVD mortality/morbidity (low strength of evidence). Low-strength evidence from prospective cohort studies supports an association between sodium intake and all-cause mortality but evidence was inconsistent regarding an association with combined CVD morbidity/mortality and a lack of association with stroke risk.
Use of potassium salt substitutes in place of sodium chloride and increased potassium intake itself significantly decrease blood pressure (moderate SoE), but evidence is insufficient to assess their effect on risk for hypertension or longer-term chronic conditions or the potential moderating effects of other factors. Evidence from prospective cohort studies is insufficient to assess associations of potassium status with outcomes of interest.
Conclusions. Dietary sodium reduction, increased potassium intake, and use of potassium-containing salt substitutes significantly decrease blood pressure, but their effects on longer term chronic disease outcomes, particularly CVD and CHD morbidity and mortality, need more research.