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Just over a decade ago, the BMJ found itself in the eye of the storm about dietary salt (BMJ 1996;312:1239-40). We had published the Intersalt study some years previously; it concluded that populations with high average intakes of salt were likely to have higher average blood pressures. But the salt producers' trade organisation, the Salt Institute, had criticised the study's methods and asked the investigators to hand over their raw data for reanalysis. A reanalysis was done—by the original investigators—and published in the BMJ (BMJ 1996;312:1249-53). The findings were the same.
It's worth remembering this skirmish in the war on dietary salt, now that the battle around the evidence linking salt and heart disease has largely been won. At the time we knew that dietary salt was linked to increased blood pressure, and over the next decade the link to actual cardiovascular disease grew stronger. So did the evidence from randomised trials that reducing salt in the diet reduced blood pressure. But still the food industry's fight against restrictions continued.
At the time they could argue that the long term benefits of reducing salt on cardiovascular disease had not been shown in randomised trials—but not any longer. This week the BMJ publishes what may be the final bugle call in the battle of the evidence. Nancy Cook and colleagues followed up people who took part in two randomised trials of dietary salt reduction to see whether reductions in blood pressure converted into reductions in cardiovascular events (p 885 doi: 10.1136/bmj.39147.604896.55). They gathered data on three quarters of the original participants and found that, after 10-15 years, the risk of cardiovascular events was more than 25% lower in people who had cut their salt intake for at least 18 months.
Such hard evidence is at last bringing the food industry to the negotiating table. Voluntary limits and food labelling, as adopted by the UK's Food Standards Agency and the European Union, have brought some progress from the industry, as has the “carrot” of growing markets for healthy foods, but they are unlikely to bring enough muscle to bear on a powerful industry practised in the arts of mitigation and delay. As Francesco Cappuccio says in his editorial (p 859 doi: 10.1136/bmj.39175.364954.BE), real progress will need the additional “stick” of legislation. Most salt in developed countries is consumed in bread and processed foods, and much of it is consumed outside the home in canteens and sandwich bars, so a population-wide policy of salt reduction will come only through pressure on the food and catering industries. The current policy—encouraging consumers to make sensible choices—effectively abandons the poor and uninformed, increasing social inequities.
While we wait for mandatory food labelling and firm limits on salt in processed foods across Europe, what can health professionals do to reduce the impact of dietary salt on people's health? Cappuccio suggests that baseline assessment of salt intake should be part of the UK's National Service Framework. A 24 hour urinary collection is cheaper than testing cholesterol. You might try talking salt in your next consultation.