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Abstract

Although meta-analyses of randomized controlled trials (RCTs) of salt reduction report a reduction in the level of blood pressure (BP), the effect of reduced dietary salt on cardiovascular disease (CVD) events remains unclear. We searched for RCTs with follow-up of at least 6 months that compared dietary salt reduction (restricted salt dietary intervention or advice to reduce salt intake) to control/no intervention in adults, and reported mortality or CVD morbidity data. Outcomes were pooled at end of trial or longest follow-up point. Seven studies were identified: three in normotensives, two in hypertensives, one in a mixed population of normo- and hypertensives and one in heart failure. Salt reduction was associated with reductions in urinary salt excretion of between 27 and 39 mmol/24 h and reductions in systolic BP between 1 and 4 mm Hg. Relative risks (RRs) for all-cause mortality in normotensives (longest follow-up-RR: 0.90, 95% confidence interval (CI): 0.58-1.40, 79 deaths) and hypertensives (longest follow-up RR 0.96, 0.83-1.11, 565 deaths) showed no strong evidence of any effect of salt reduction CVD morbidity in people with normal BP (longest follow-up: RR 0.71, 0.42-1.20, 200 events) and raised BP at baseline (end of trial: RR 0.84, 0.57-1.23, 93 events) also showed no strong evidence of benefit. Salt restriction increased the risk of all-cause mortality in those with heart failure (end of trial RR 2.59, 1.04-6.44, 21 deaths).We found no information on participant's health-related quality of life. Despite collating more event data than previous systematic reviews of RCTs (665 deaths in some 6,250 participants) there is still insufficient power to exclude clinically important effects of reduced dietary salt on mortality or CVD morbidity. Our estimates of benefits from dietary salt restriction are consistent with the predicted small effects on clinical events attributable to the small BP reduction achieved.

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Cost-effectiveness of interventions to reduce dietary salt intake.

L. J. Cobiac, T. Vos, J. L. Veerman (2010)

To evaluate population health benefits and cost-effectiveness of interventions for reducing salt in the diet. Proportional multistate life-table modelling of cardiovascular disease and health sector cost outcomes over the lifetime of the Australian population in 2003. The current Australian programme of incentives to the food industry for moderate reduction of salt in processed foods; a government mandate of moderate salt limits in processed foods; dietary advice for everyone at increased risk of cardiovascular disease and dietary advice for those at high risk. Costs measured in Australian dollars for the year 2003. Health outcomes measured in disability-adjusted life years (DALY) averted over the lifetime. Mandatory and voluntary reductions in the salt content of processed food are cost-saving interventions under all modelled scenarios of discounting, costing and cardiovascular disease risk reversal (dominant cost-effectiveness ratios). Dietary advice targeting individuals is not cost-effective under any of the modelled scenarios, even if directed at those with highest blood pressure risk only (best case median cost-effectiveness A$100 000/DALY; 95% uncertainty interval A$64 000/DALY to A$180 000/DALY). Although the current programme that relies on voluntary action by the food industry is cost-effective, the population health benefits could be 20 times greater with government legislation on moderate salt limits in processed foods. Programmes to encourage the food industry to reduce salt in processed foods are highly recommended for improving population health and reducing health sector spending in the long term, but regulatory action from government may be needed to achieve the potential of significant improvements in population health.