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Database of Abstracts of Reviews of Effects (DARE): Quality-assessed Reviews [Internet]. York (UK): Centre for Reviews and Dissemination (UK); 1995-.

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Database of Abstracts of Reviews of Effects (DARE): Quality-assessed Reviews [Internet].

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Effect of lower sodium intake on health: systematic review and meta-analyses

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Review published: .

CRD summary

This review found that reduced sodium intake lowered blood pressure and reduced the risk of stroke, without adversely affecting blood lipid levels or renal function. Although some of the results were based on non-randomised cohort studies which are prone to bias, the large size of this review means its results are likely to be reliable.

Authors' objectives

To assess the effect of decreased sodium intake on blood pressure, cardiovascular disease and potentially related adverse effects.

Searching

A literature search was conducted to identify relevant existing systematic reviews. To identify studies published after these reviews MEDLINE, EMBASE, CENTRAL, LILACS and WHO International Clinical Trials Registry Platform were searched in August 2011 without language restrictions. Search terms were presented. Reference lists of included articles were checked and relevant researchers contacted to identify further studies.

Study selection

Randomised controlled trials (RCTs), quasi-randomised trials, non-randomised trials and prospective cohort studies were all eligible for inclusion. RCTs had to compare a lowered sodium intake group to a higher sodium group, with at least a 40mmol/day difference in sodium intake between groups. RCTs had to use urinary sodium excretion from 24 hour urine collection to estimate actual sodium intake. Trials had to be at least four weeks long. Prospective cohort studies had to have duration of at least one year. Trials that used concomitant interventions only in the intervention arm were excluded, as were studies where participants were acutely ill, had HIV or had been admitted to hospital. Outcomes of interest included: blood pressure; all-cause mortality; cardiovascular mortality and morbidity; and adverse effects such as changes in blood lipids, catecholamine levels or renal function.

The most common means of altering sodium intake in the RCTs was thorough dietary advice, but education, provision of reduced-sodium foods and provision of sodium pills were also used. Studies were conducted worldwide, including in the UK.

Two reviewers independently screened the search results to identify relevant studies.

Assessment of study quality

For RCTs, risk of bias was assessed by considering sequence generation, allocation concealment, blinding, selective reporting, loss to follow-up and completeness of outcome reporting. For cohort studies, risk of bias was assessed by considering methods of measuring exposure, collecting outcome data and selecting participants. Overall quality of the evidence was assessed using GRADE criteria.

It appeared that at least two reviewers performed the quality assessment.

Data extraction

For blood pressure and other continuous outcomes, the mean difference between lower and higher sodium intake groups was extracted, with 95% confidence intervals. For cardiovascular events the risk ratio or hazard ratio between groups was extracted, with 95% confidence intervals. In cohort studies the lowest and highest sodium intake groups were compared.

Two reviewers independently undertook the data extraction, which was checked by a third; disagreements were resolved by discussion.

Methods of synthesis

Results were synthesised in a random-effects meta-analysis using the inverse-variance method. Heterogeneity was assessed using Ι²; Ι² greater than 75% indicated an important level of heterogeneity. Several subgroup analyses were conducted to explore potential causes of heterogeneity. Funnel plots were produced to check for small-study bias.

Results of the review

Thirty-seven RCTs reported blood pressure and adverse effect outcomes; 14 cohort studies and five RCTs reported cardiovascular outcomes. There were also nine trials and one cohort study in children. Most RCTs had duration of less than three months (range four weeks to 36 months). Cohort studies had follow-up times ranging from 3.8 to 22 years. RCTs were judged to be at low risk of serious bias. Cohort studies were judged to have little risk of serious bias beyond that inherent in observational studies. Studies in children were judged to be at risk of bias.

Blood pressure and adverse events

Reduced sodium intake lowered resting systolic blood pressure (MD 3.39mmHg, 95% CI 2.46 to 4.31; 36 studies, 6,736 participants; Ι²=65%) and lowered resting diastolic blood pressure (MD 1.54mmHg, 95% CI 0.98 to 2.11). Systolic blood pressure lowering was greater in participants with hypertension (MD 4.06 mmHg, 95% CI 2.96 to 5.15; 24 studies; Ι²=29%), than in those without hypertension (MD 1.38 mmHg, 95% CI 0.02 to 2.74; seven studies; Ι²=38%). Results from a number of other subgroup analyses were presented. Reduced sodium intake was found to have no adverse effect on lipid levels (11 studies, 2,339 participants), adrenaline levels, catecholamine levels or renal function. There was no evidence of publication bias.

Mortality and cardiovascular events

Higher sodium intake was associated with a greater risk of stroke generally (RR 1.24, 95% CI 1.08 to 1.43; 10 studies, 72,878 participants; Ι²=49%), of fatal strokes in particular (RR 1.63, 95% CI 1.27 to 2.10; three studies, 48,645 participants; Ι²=33%) and with a greater risk of fatal coronary heart disease (RR 1.32, 95% CI 1.13 to 1.53; three studies, 30,670 participants; Ι²=0). Higher sodium intake increased the risk of all-cause mortality and cardiovascular events generally but results were not statistically significant.

Children

In studies in children reduced sodium intake lowered resting systolic blood pressure (MD 0.84mmHg, 95% CI 0.25 to 1.43; nine studies; Ι²=21%) and diastolic blood pressure (MD 0.87mmHg, 95% CI 0.14 to 1.6). No studies in children reported data on adverse events.

Authors' conclusions

Reduced sodium intake lowered blood pressure in adults, with no effect on blood lipids, catecholamine levels or renal function. Reduced sodium intake also reduced blood pressure in children. Lower sodium intake was associated with a reduced risk of stroke and fatal coronary heart disease.

CRD commentary

This was a well conducted review with a clear research question and appropriate inclusion criteria. A thorough search was performed. It seemed that action was taken to reduce reviewer error and bias in the review. Study quality was assessed. Randomised controlled trials were deemed to be at low risk of serious bias. Cohort studies were judged to be at low risk of bias, but such studies were generally more prone to bias as they were not randomised comparisons. A large number of studies and participants were included in the review. Studies were synthesised in a number of meta-analyses.

Despite the potential for bias from including non-randomised studies, the large size of this review suggests that its results, and the authors’ conclusions, are likely to be reliable.

Implications of the review for practice and research

Practice: The authors did not make any recommendations for medical practice.

Research: The authors suggested that randomised controlled trials of sodium intake measuring cardiovascular outcomes were needed to strengthen the evidence base.

Funding

WHO funding; Kidney Evaluation Association Japan; Japan and Korean government support.

Bibliographic details

Aburto NJ, Ziolkovska A, Hooper L, Elliott P, Cappuccio FP, Meerpohl JJ. Effect of lower sodium intake on health: systematic review and meta-analyses. BMJ 2013; 346:f1326. [PMC free article: PMC4816261] [PubMed: 23558163]

Indexing Status

Subject indexing assigned by NLM

MeSH

Blood Pressure; Cardiovascular Diseases /diet therapy /metabolism /prevention & control; Catecholamines /metabolism; Diet, Sodium-Restricted; Female; Humans; Hypertension /diet therapy /metabolism /prevention & control; Kidney /metabolism; Lipid Metabolism; Male; Prospective Studies; Public Health; Randomized Controlled Trials as Topic; Sodium Chloride, Dietary /administration & dosage

AccessionNumber

12013018993

Database entry date

11/04/2013

Record Status

This is a critical abstract of a systematic review that meets the criteria for inclusion on DARE. Each critical abstract contains a brief summary of the review methods, results and conclusions followed by a detailed critical assessment on the reliability of the review and the conclusions drawn.

Copyright © 2014 University of York.
Bookshelf ID: NBK132099

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