Systematic review of long term effects of advice to reduce dietary salt in adults

doi:10.1136/bmj.325.7365.628

BMJ 2002;325:628 ( 21 September )

Papers

Systematic review of long term effects of advice to reduce dietary salt in adults

Lee Hooper, research fellow in evidence based care and systematic review, ^a Christopher Bartlett, research associate in health services research, ^b George Davey Smith, professor of clinical epidemiology, ^b Shah Ebrahim, professor in epidemiology of ageing. ^b

^a MANDEC, University Dental Hospital of Manchester, Manchester M15 6FH, ^b Department of Social Medicine, MRC Health Services Research Collaboration, University of Bristol, Bristol BS8 2PR

Correspondence to: L Hooper
lee.hooper{at}man.ac.uk

Objective: To assess the long term effects of adviceto restrict dietary sodium in adults with and withouthypertension.
Design: Systematic review and meta-analysis of randomisedcontrolledtrials.
Data sources: Cochrane library, Medline, Embase, andbibliographies.
Study selection: Unconfounded randomised trials that aimedto reduce sodium intake in healthy adults over at least 6 months.Inclusion decisions, validity and data extraction were duplicated.Random effects meta-analysis, subgrouping, sensitivity analysis,and meta-regression wereperformed.
Outcomes: Mortality, cardiovascular events, blood pressure,urinary sodium excretion, quality of life, and use of antihypertensivedrugs.
Results: Three trials in normotensive people (n=2326),five trials in those with untreated hypertension (n=387), andthree trials in people being treated for hypertension (n=801)were included, with follow up from six months to seven years.The large high quality (and therefore most informative) studiesused intensive behavioural interventions. Deaths and cardiovascularevents were inconsistently defined and reported. There were 17deaths, equally distributed between intervention and control groups.Systolic and diastolic blood pressures were reduced (systolicby 1.1 mm Hg, 95% confidence interval 1.8 to 0.4 mm Hg; diastolicby 0.6 mm Hg, 1.5 to $-$ 0.3 mm Hg) at 13 to 60 months, as was urinary24 hour sodium excretion (by 35.5 mmol/24 hours, 47.2 to 23.9).Degree of reduction in sodium intake and change in blood pressurewere notrelated.
Conclusions: Intensive interventions, unsuited to primarycare or population prevention programmes, provide only small reductionsin blood pressure and sodium excretion, and effects on deathsand cardiovascular events are unclear. Advice to reduce sodiumintake may help people on antihypertensive drugs to stop theirmedication while maintaining good blood pressurecontrol.

What is already known on this topic
Restricting sodium intake in people with hypertension reduces blood pressure

Long term effects (on blood pressure, mortality, and morbidity) of reduced salt intake in people with and without hypertension are unclear

What this study adds
Few deaths and cardiovascular events have been reported in salt reduction trials

Meta-analysis shows that blood pressure was reduced (systolic by 1.1 mm Hg, diastolic by 0.6 mm Hg) at 13 to 60 months, with a reduction in sodium excretion of almost a quarter (35.5 mmol/24 hours)

The interventions used were highly intensive and unsuited to primary care or population prevention programmes

Lower salt intake may help people on antihypertensive drugs to stop their medication while maintaining good control of blood pressure, but there are doubts about effects of sodium reduction on overall health

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Rapid Responses:

Read all Rapid Responses

Beyond risk factors (2), in the war against Atherosclerosis.: Sergio Stagnaro
bmj.com, 20 Sep 2002 [Full text]
Reduction of dietary salt may be more appropriate in selected hypertensive patients groups.: John A Sayer
bmj.com, 23 Sep 2002 [Full text]
Distrust: antonio lopez pe�a
bmj.com, 23 Sep 2002 [Full text]
Re: Distrust: John P Heptonstall
bmj.com, 24 Sep 2002 [Full text]
SALT: Graham A. MacGregor, et al.
bmj.com, 27 Sep 2002 [Full text]
Sodium, salt and hypertension: James Laughton
bmj.com, 27 Sep 2002 [Full text]
PATIENT EDUCATION: Dr Rita Pal
bmj.com, 28 Sep 2002 [Full text]
SALT OVERLOAD: Sunil Bhandari
bmj.com, 30 Sep 2002 [Full text]
Neither the safety nor benefit of long term reduced sodium intake has been established in hypertensi: Michael H. Alderman
bmj.com, 9 Oct 2002 [Full text]
Salt and Health: Ivan J Perry
bmj.com, 10 Oct 2002 [Full text]
Response to Hooper et al: Nicholas J Wald, et al.
bmj.com, 17 Oct 2002 [Full text]
Salt consumption and commercial interests: Hugh E de Wardener
bmj.com, 30 Jan 2003 [Full text]