Salt reduction to prevent hypertension: the reasons of the controversy.

There is a causal relationship between dietary salt intake and blood pressure. A reduction in salt intake from the current world average of ∼10 g/day to the WHO recommended level of <5 g/day, lowers blood pressure and reduces the risk of cardiovascular disease and all-cause mortality. However, a few cohort studies have claimed that there is a J-shaped relationship between salt intake and cardiovascular risk, i.e. both high and low salt intakes are associated with an increased risk. These cohort studies have several methodological problems, including reverse causality, and inaccurate and biased estimation of salt intake, e.g. from a single spot urine sample with formulas. Recent studies have shown that the formulas used to estimate salt intake from spot urine cause a spurious J-curve. Research with inappropriate methodology should not be used to refute the robust evidence on the enormous benefits of population-wide reduction in salt intake. Several countries, e.g. Finland, the UK, have successfully reduced salt intake, which has resulted in falls in population blood pressure and deaths from stroke and ischaemic heart disease. Every country should develop and implement a coherent, workable strategy to reduce salt intake. Even a modest reduction in salt intake across the whole population will lead to a major improvement in public health, along with huge cost-savings to the healthcare service.