Table 3 Dietary salt and blood pressure

Case study

A dose-response relationship between dietary salt intake and blood pressure has been consistently demonstrated in animal studies and in ecological, cohort and intervention studies in humans. A recent randomised controlled trial has also shown that dietary and behavioural counselling to limit salt intake reduces the incidence of 'hard' cardiovascular endpoints, thus surely fulfilling any reasonable definition of an evidence-based public health intervention. The linear model of translation suggests that all that remains is for 'sodium reduction interventions' of this kind to be implemented as widely as possible [20, 21].

However, an estimated 80% of dietary salt intake in Westernised countries comes from bread and processed foods rather than from discretionary use. Even if it were feasible to roll out intensive counselling across the population, shifting the population distribution of salt intake is therefore more likely to depend on changing the composition of processed foods. The greatest potential for translation into population health improvement may therefore lie not in disseminating and implementing a 'proven' intervention but in using other, predominantly epidemiological evidence to influence policymakers and the non-statutory corporate social responsibilities of food manufacturers. It may not be possible to demonstrate the population-level effectiveness (or otherwise) of regulatory interventions on food labelling or the salt content of processed foods until policymakers, somewhere, decide to intervene in this way as a 'natural experiment'; the effects could then be evaluated through enhanced population dietary and health surveillance [36].