Background Non-communicable disease prevention strategies now prioritise four major risk factors: food, tobacco, alcohol and physical activity. Dietary salt intake remains much higher than recommended, leading to high blood pressure, cardiovascular disease and gastric cancer. Substantial reductions in salt intake are therefore urgently needed. However, debates continue about the most effective approaches. To inform future prevention programmes, we therefore systematically reviewed the evidence on possible interventions. We further hypothesised an effectiveness hierarchy, that “upstream, structural” policy-based population strategies are more powerful than “downstream, agentic” approaches targeting individuals.
Methods We searched six electronic databases (CDSR, CRD, MEDLINE, SCI, SCOPUS and the Campbell Library) using a pre-piloted search strategy focusing on the effectiveness of population interventions to reduce salt intake. Retrieved papers were independently screened, appraised and graded for quality by two researchers. Extracted data were categorised using nine stages along the McLaren’s agentic/structural continuum, from “downstream”: individual dietary counselling, through worksite and community interventions, media campaigns, nutrition labelling, voluntary and mandatory reformulation, to the most “upstream” regulatory and fiscal interventions. We also considered comprehensive strategies involving multiple components. We used a narrative synthesis and formally investigated evidence to support or refute an effectiveness hierarchy.
Results After screening 2526 candidate papers, 72 were included in this systematic review (51 empirical and 21 modelling studies). Some papers described several interventions. Quality was variable.
Multi-component strategies involving both upstream and downstream interventions, generally achieved the biggest reductions in salt consumption across an entire population, most notably −4 g/day in Finland and Japan, −3 g/day in Turkey and −1.5 g/day in the UK. Tax interventions were considered in a few modelling studies where effects were mixed and modest.
Mandatory reformulation achieved reductions of at least −1.45 g/day in three separate countries, more than food labelling or worksite interventions (each typically averaging −1.2 g/day, but with a wide range). Smaller population benefits came from health education media campaigns (−0.2 g/day or less) or interventions in schools (ranging from −0.2 g/day to −0.7 g/day).
Although dietary advice achieved −2 g/day reductions in compliant volunteers in trials, much smaller reductions might be anticipated in unselected individuals in the general population.
Conclusion Our systematic review supports the concept of an “effectiveness hierarchy”. Comprehensive strategies involving multiple components and “upstream” population-wide policies achieve larger, population-wide reductions in salt consumption than more “downstream” interventions such as reformulation, food labelling, worksite interventions or individual approaches.