To assess the long term effects of advice to restrict dietary sodium in adults with and without hypertension.
Systematic review and meta-analysis of randomised controlled trials.
Cochrane library, Medline, Embase, and bibliographies.
Unconfounded randomised trials that aimed to 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 were performed.
Mortality, cardiovascular events, blood pressure, urinary sodium excretion, quality of life, and use of antihypertensive drugs.
Three trials in normotensive people (n=2326), five trials in those with untreated hypertension (n=387), and three 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) studies used intensive behavioural interventions. Deaths and cardiovascular events were inconsistently defined and reported. There were 17 deaths, equally distributed between intervention and control groups. Systolic and diastolic blood pressures were reduced (systolic by 1.1 mm Hg, 95% confidence interval 1.8 to 0.4 mm Hg; diastolic by 0.6 mm Hg, 1.5 to −0.3 mm Hg) at 13 to 60 months, as was urinary 24 hour sodium excretion (by 35.5 mmol/24 hours, 47.2 to 23.9). Degree of reduction in sodium intake and change in blood pressure were not related.
Intensive interventions, unsuited to primary care or population prevention programmes, provide only small reductions in blood pressure and sodium excretion, and effects on deaths and cardiovascular events are unclear. Advice to reduce sodium intake may help people on antihypertensive drugs to stop their medication while maintaining good blood pressure control.
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