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

BMJ 2013; 346 doi: http://dx.doi.org/10.1136/bmj.f1326 (Published 04 April 2013) Cite this as: BMJ 2013;346:f1326
  1. Nancy J Aburto, scientist1,
  2. Anna Ziolkovska, intern1,
  3. Lee Hooper, senior lecturer in research synthesis and nutrition2,
  4. Paul Elliott, professor3,
  5. Francesco P Cappuccio, Cephalon professor of cardiovascular medicine and epidemiology4,
  6. Joerg J Meerpohl, deputy director5
  1. 1Nutrition Policy and Scientific Advice Unit, Department of Nutrition for Health and Development, World Health Organization, 1211 Geneva 27, Switzerland
  2. 2Norwich Medical School, University of East Anglia, Norwich, UK
  3. 3Department of Epidemiology and Biostatistics and MRC-HPA Centre for Environment and Health, Imperial College London, UK
  4. 4University of Warwick, World Health Organization Collaborating Centre for Nutrition, Warwick Medical School, Division of Mental Health and Wellbeing, Coventry, UK
  5. 5German Cochrane Centre, Institute of Medical Biometry and Medical Informatics, University Medical Center Freiburg, Freiburg, Germany
  1. Correspondence to: N J Aburto nancy.aburto{at}wfp.org
  • Accepted 18 February 2013

Abstract

Objective To assess the effect of decreased sodium intake on blood pressure, related cardiovascular diseases, and potential adverse effects such as changes in blood lipids, catecholamine levels, and renal function.

Design Systematic review and meta-analysis.

Data sources Cochrane Central Register of Controlled Trials, Medline, Embase, WHO International Clinical Trials Registry Platform, the Latin American and Caribbean health science literature database, and the reference lists of previous reviews.

Study selection Randomised controlled trials and prospective cohort studies in non-acutely ill adults and children assessing the relations between sodium intake and blood pressure, renal function, blood lipids, and catecholamine levels, and in non-acutely ill adults all cause mortality, cardiovascular disease, stroke, and coronary heart disease.

Study appraisal and synthesis Potential studies were screened independently and in duplicate and study characteristics and outcomes extracted. When possible we conducted a meta-analysis to estimate the effect of lower sodium intake using the inverse variance method and a random effects model. We present results as mean differences or risk ratios, with 95% confidence intervals.

Results We included 14 cohort studies and five randomised controlled trials reporting all cause mortality, cardiovascular disease, stroke, or coronary heart disease; and 37 randomised controlled trials measuring blood pressure, renal function, blood lipids, and catecholamine levels in adults. Nine controlled trials and one cohort study in children reporting on blood pressure were also included. In adults a reduction in sodium intake significantly reduced resting systolic blood pressure by 3.39 mm Hg (95% confidence interval 2.46 to 4.31) and resting diastolic blood pressure by 1.54 mm Hg (0.98 to 2.11). When sodium intake was <2 g/day versus ≥2 g/day, systolic blood pressure was reduced by 3.47 mm Hg (0.76 to 6.18) and diastolic blood pressure by 1.81 mm Hg (0.54 to 3.08). Decreased sodium intake had no significant adverse effect on blood lipids, catecholamine levels, or renal function in adults (P>0.05). There were insufficient randomised controlled trials to assess the effects of reduced sodium intake on mortality and morbidity. The associations in cohort studies between sodium intake and all cause mortality, incident fatal and non-fatal cardiovascular disease, and coronary heart disease were non-significant (P>0.05). Increased sodium intake was associated with an increased risk of stroke (risk ratio 1.24, 95% confidence interval 1.08 to 1.43), stroke mortality (1.63, 1.27 to 2.10), and coronary heart disease mortality (1.32, 1.13 to 1.53). In children, a reduction in sodium intake significantly reduced systolic blood pressure by 0.84 mm Hg (0.25 to 1.43) and diastolic blood pressure by 0.87 mm Hg (0.14 to 1.60).

Conclusions High quality evidence in non-acutely ill adults shows that reduced sodium intake reduces blood pressure and has no adverse effect on blood lipids, catecholamine levels, or renal function, and moderate quality evidence in children shows that a reduction in sodium intake reduces blood pressure. Lower sodium intake is also associated with a reduced risk of stroke and fatal coronary heart disease in adults. The totality of evidence suggests that most people will likely benefit from reducing sodium intake.

Footnotes

  • We thank the members of the WHO Nutrition Guidance Expert Advisory Group (WHO NUGAG) for their input and comments on the manuscript; the stakeholders who provided their feedback on scoping the review; and Sharnali Das for screening manuscripts for inclusion and data extraction. PE is a senior investigator for the National Institute for Health Research (NIHR). The views expressed are those of the authors and not necessarily those of the National Health Service, the NIHR, or the Department of Health. FPC and JJM contributed equally to the study.

  • Contributors: The priority questions to be addressed for the review were discussed and developed by the WHO NUGAG Subgroup on Diet and Health in March 2011 and the protocol was subsequently developed to address the requested questions by the WHO NUGAG Subgroup on Diet and Health. NJA and AZ ran the searches, carried out the assessment of papers for inclusion, extracted data, did the validity assessment, and prepared the first draft of the report submitted for review by the WHO NUGAG Subgroup on Diet and Health. NJA completed the data analyses. NJA and JM developed the first GRADE evidence profiles. The WHO NUGAG Subgroup on Diet and Health reviewed earlier drafts and contributed to the analysis and GRADE assessment. NJA wrote the first draft of the manuscript. LH, PE, FPC, and JJM provided substantial intellectual input on research methods and interpretation of results. All authors read, provided input, and agreed the final draft of the manuscript. WHO agreed with the publication of this systematic review in a scientific journal as it serves as the background evidence review for updating the WHO guideline on sodium intake for adults and for the establishment of a guideline on sodium intake in children and should therefore be widely available.

  • Funding: This review was supported by WHO funds, the Kidney Evaluation Association Japan, and the governments of Japan and Republic of Korea.

  • Competing interests: All authors have completed the ICMJE uniform disclosure form at www.icmje.org/coi_disclosure.pdf (available on request from the corresponding author) and declare: LH, FPC, PE, and JJM received funding from WHO to attend NUGAG Subgroup of Diet and Health meetings, PE receives support from the National Institute for Health Research Biomedical Research Centre based at Imperial College Healthcare NHS Trust and Imperial College London, FPC is an unpaid member of Consensus Action on Salt and Health (CASH), World Action on Salt and Health (WASH), unpaid advisor to the WHO and the PAHO, a member of the National Heart Forum and former member of the executive committee and trustee of the British Hypertension Society, PE is an unpaid member of CASH, WASH, and an unpaid advisor to WHO; no further financial support from any organisation for the submitted work that might have an interest in the submitted work in the previous three years; no other relationships or activities that could appear to have influenced the submitted work. NJA was a staff member of WHO at the time this work was conducted. The author alone is responsible for the views expressed in this publication and they do not necessarily represent the views, decisions, or policies of WHO.

  • Ethical approval: Not required.

  • Data sharing: The datasets are available from the corresponding author at nancy.aburto@wfp.org.

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