Background A range of policies aim to reduce salt intake; however, their relative effects remain unclear. We undertook a narrative synthesis of existing evidence to determine the most promising approaches.
Methods We searched for systematic reviews, then empirical and modelling studies of salt reduction policies in six electronic databases. Reference lists of retrieved articles were screened and key informants were asked to identify further reviews and empirical/modelling studies. Items were assessed for inclusion and data were extracted into predesigned forms. Results were categorised using a modified version of the marketing four P’s framework: Price, Product, Place and Promotion.
Results Price: A US sodium excise tax may reduce sodium intake (by 6%), systolic blood pressure (by 0.9mmHg), stroke (by 10%) and myocardial infarction (by 5%) over the lifetime of those aged 40 – 85 years. (One modelling study)
Product: Voluntary US salt limits might achieve lifetime reductions in sodium intake (-9.5%), blood pressure (-1.25mmHg), myocardial infarction (-5%) and stroke (-10%). In Australia, mandatory salt limits could reduce cardiovascular disease (by 18%) but only by 1% with voluntary intervention. (Two modelling studies)
Promotion: Intensive advice, support and encouragement to restrict dietary sodium intake led to significant long term reductions in urinary sodium excretion, systolic blood pressure (-1.1mmHg) and disease burden (-0.5%.) Interventions involving advertising/marketing/labelling have only been evaluated within multi-component interventions. (One systematic review.)
Place: Place-based interventions (targeting schools, workplaces and community settings) have only been evaluated within multi-component interventions.
Multi-component interventions: The UK FSA product and promotion-based initiatives reduced salt intake by approximately 10%. Two modelling studies estimate that similar interventions in low- and middle-income countries might achieve a 15% reduction in salt consumption, globally averting perhaps 1 million deaths and 21 million disability-adjusted life years annually. Modelling estimates from Norway suggest that combining taxes and subsidies with product and price interventions might reduce daily salt intake by 6g. Survey data reveal that in Finland between 1979 – 2002, a comprehensive and mandatory nutrition intervention (using regulations targeting price, product, place and promotion) reduced urinary sodium excretion from 13 to 10 g/day in men and from 10.5 to 7.5g/day in women. (Two empirical studies and three modelling studies)
Conclusion There is patchy evidence on the effectiveness of policy actions to reduce dietary salt intake. Dietary advice can achieve modest benefits. Modelling suggests taxes and reformulation may be effective (particularly when mandatory). Empirical and modelling studies indicate multi-component interventions could be particularly powerful.
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