There are a multitude of different types of studies that have examined the effects of salt on health. They range from small laboratory-based projects to large population-based investigations. While the results of individual pieces of work have varied, the totality of the evidence is incontrovertible – most of the world’s population eats far more salt than it needs and the adverse effects on global health are enormous.
Salt intake and blood pressure
The clearest adverse effect of salt is on blood pressure. Observational studies comparing individuals and populations that eat different amounts of salt show a striking association of salt consumption with blood pressure. The more salt eaten, the higher is the blood pressure and the greater is the increase in blood pressure with age. And this is true not just for people with hypertension, but for the majority of the world’s population. Salt consumption is above that required for good health in most of the world’s population. Salt consumption above this level will cause some rise in the blood pressure of billions of people worldwide every year with consequent effects on the risk of stroke, heart attack, heart failure and kidney disease.
Salt reduction and blood pressure
Experimental studies confirm the observational studies. Overviews of more than thirty randomised trials in which people were assigned to eat different amounts of salt showed clear benefits of reducing salt consumption on blood pressure. And the greater the salt reduction, the greater was the blood pressure reduction. Once again, the effect was observed not just in people with hypertension but also in people with normal blood pressure levels.
Salt reduction and health outcomes
There are strong data linking salt consumption to major adverse health outcomes. First, salt has clear effects on blood pressure, and high blood pressure is the biggest single cause of death in the world. Blood pressure lowering with drug therapies bring about substantially reduced risks of heart attack, stroke and heart failure and there is every expectation that the same effects would be achieved by blood pressure reduction through reduced salt consumption.
While studies of the direct effects of salt on mortality have shown varied results, the majority show adverse effects and those that do not have significant limitations in their design. Most recently, long-term follow-up of the participants of two large-scale randomised trials have shown that people assigned to reduced salt 10-15 years earlier had a 25-30% lower risk of cardiovascular events than those who continued with their usual salty diets. This evidence has greatly strengthened the argument for salt reduction.
Summaries and Reports
Reducing Salt Intake in Populations
WHO Forum and Technical Meeting on Reducing Salt Intake in Populations.
Consensus Action on Salt and Health website – Evidence
Why 6g, A summary of the scientific evidence for the salt reduction target
Reviews and meta-analysis
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