Every adult should consider switch to potassium-enriched salt

In contrast to prior failed sodium reduction efforts, the simplicity of the intervention and the joint benefits of sodium reduction and potassium supplementation provide a very high likelihood of success. Switching Australia’s, and the world’s, salt supply to potassium-enriched salt should be a priority.

THE adverse effects of excess dietary sodium intake on blood pressure levels are widely accepted. The magnitude of the excess consumption is less well appreciated. Most of the world’s population now eats dietary sodium, mostly in the form of salt, at about five times the level consumed during a million years of hominid evolution.

Current average Australian consumption of sodium is about 3.8 g per day (9.6 g salt). This is five times the estimated sodium contained in a Paleolithic diet, which contains about 0.7 g per day (1.75 g salt). At the same time, dietary potassium intake is far below the level our physiology evolved on. Average adult Australian consumption is about 2.9 g per day which compares to a World Health Organization-recommended minimum of 3.5 g per day and an evolutionary intake of up to 11.0 g per day.

The reason for the gulf between actual and optimal levels of dietary sodium and potassium intake in Australia is the food system. Food processing systematically removes naturally occurring potassium from fresh fruits and vegetable and replaces it with added sodium.

The key problem with excess sodium consumption is that it results in high blood pressure and greatly increased risks of stroke, heart attacks, kidney disease and heart failure. Eating too much sodium also appears to be one of the main reasons that blood pressure goes up as we age. At the same time, lower levels of dietary potassium are also independently associated with higher blood pressure and increased cardiovascular risks.

Proven benefits of potassium-enriched salt

Potassium-enriched salts (salt substitutes) are a practical way of reducing dietary sodium intake and achieve blood pressure lowering by jointly reducing dietary sodium and increasing dietary potassium. The blood pressure-lowering effects of sodium reduction, potassium supplementation and potassium-enriched salts have been established for decades. What was unknown until recently was the effect of changing sodium and potassium intake on cardiovascular outcomes. The reason for this uncertainty has been a combination of factors, but mostly it has been caused by the misinterpretation of weak observational epidemiology and the absence of definitive large-scale trials.

The state of the evidence was transformed with the completion of the Salt Substitute and Stroke Study. One year ago, in September 2021, the trial reported data for 20 995 people randomly allocated to potassium-enriched salt (25% potassium chloride and 75% sodium chloride) or regular salt (100% sodium chloride). Study participants were followed for 5 years, during which time more than 3000 strokes and 4000 deaths were recorded. The trial showed that the potassium-enriched salt reduced the risks of stroke by 14% (P = 0.006), major cardiovascular events by 13% (P < 0.001), and premature death by 12% (P < 0.001).

The Salt Substitute and Stroke Study was designed on the premise that the potassium-enriched salt would reduce blood pressure and that lower levels of blood pressure would reduce cardiovascular risks. The magnitude of the effects seen in the trial were exactly those anticipated from the mean 3.3 mmHg lowering of systolic blood pressure achieved. This means that potassium-enriched salt should provide protection for anyone who has their blood pressure lowered by using it, with the size of the protection achieved directly related to how big the blood pressure reduction is.

The Salt Substitute and Stroke Study also showed that potassium-enriched salt can be provided safely, even in situations where concerns about risks have been raised. The trial population was mostly older people with known vascular disease who were at higher than average risk of having occult kidney disease. High blood potassium levels are a risk of potassium-enriched salt use in this situation, and hyperkalaemia was the pre-specified safety outcome for the study. Possible hyperkalaemia was observed infrequently (just 331 suspected events), and rates were the same across the randomised groups (rate ratio, 1.04; P = 0.76). Mitigation of hyperkalaemia risks in the trial was achieved simply by asking participants to self-exclude if they had kidney disease or used a potassium supplement. There was no requirement for a clinical consultation or a test of kidney function.

This hyperkalaemia finding provides a strong indication that it will be possible to provide potassium-enriched salt safely to general populations.

A practical solution for patients

The Salt Substitute and Stroke Study, and many other studies before it, have highlighted the feasibility of achieving sustained dietary change with potassium-enriched salt.

In general, salt reduction interventions require patients to make changes to their behaviour, which they find difficult to do. For example, reducing the amount of salt they add when preparing or seasoning food can change taste. As a consequence, successful reduction in sodium intake using these interventions is usually restricted to a few highly motivated individuals and even then, it can be difficult to sustain in the long term.

Potassium-enriched salts, by contrast, are easy to use because they require only that people purchase potassium-enriched salt instead of regular salt. Usage is then the same as for regular salt and there is typically no detectable change in taste, or only a slight change, which is well tolerated. In the Salt Substitute and Stroke Study, more than 90% of participants were still using potassium-enriched salt after 5 years, which is far above the adherence rates achieved with other salt reduction programs and far better than most trials of drug therapies.

A challenge to the effectiveness of potassium-enriched salt in the Australian setting is that, for many people, most of the daily salt intake derives from packaged or processed foods purchased at the supermarket or from meals eaten out of the home in restaurants. In most cases, potassium-enriched salt could be used as a direct switch for regular salt in the preparation of processed foods, but this will be beyond the direct control of patients.

A parallel process of advocacy targeting food manufacturers, restaurant chains, and bulk ingredient suppliers will be required.

A feasible and achievable solution for the broader community

The health benefits observed in the Salt Substitute and Stroke Study are likely to be widely generalisable because they were driven by blood pressure lowering. A recent overview of 20 trials of potassium-enriched salts showed that blood pressure-lowering effects are achieved across diverse populations and geographies. It is likely that most of the Australian population, not just individuals with hypertension or established cardiovascular disease, would benefit from using a potassium-enriched salt because lower blood pressure levels throughout life are associated with lower risks of disease.

Another key feature of potassium-enriched salt is that it can be provided at low cost. Sodium chloride, which makes up regular salt, is inexpensive, and while the potassium chloride used in potassium-enriched salt costs more, it is still a low cost commodity. A recent global review showed that, on average, potassium-enriched salt was about twice as expensive as regular salt. Potassium-enriched salts had a median price of less than $3 per kilogram in low and middle-income countries, though tended to be more expensive in higher income countries such as Australia, where they are marketed as premium products.

Even so, in Australia, the personal cost of switching to potassium-enriched salt would likely be just a few dollars a year for most. An in-trial cost-effectiveness analysis done for the Salt Substitute and Stroke Study showed use of potassium-enriched salt was cost-saving from the perspective of the patient and health system because of reduced hospital costs in individuals using potassium-enriched salt.

There is real potential for making a nationwide switch, and even a global switch, to potassium-enriched salt. In the fight against iodine deficiency disorders, the past 50 years have seen the global salt supply switched from salt to iodised salt. The benefits of this switch for goitre, hypothyroidism and child development are undoubted, but iodine and salt have made for uncomfortable bedfellows. The benefits of iodine have provided salt with an unwarranted veneer of respectability.

Dietary sodium is associated with millions of cases of cardiovascular disease, stomach cancer and premature death each year. Resolution of this dilemma could be achieved with our proposed second switch of the global salt supply from iodised salt to iodised and potassium-enriched salt.

A large global collaboration built over many decades has implemented the salt iodisation program. Already, members of this partnership are exploring the feasibility of double-fortified salt with added iron to address endemic anaemia. The potential for further enriching salt with potassium is therefore highly apposite, and joint development and delivery with the iodisation program could provide both for implementation efficiencies and a greater likelihood of success at scale.

Large health gains

The potential health gains from a switch to potassium-enriched salt are very large. Modelling done for China indicates that about 1 million strokes and heart attacks could be prevented each year if the switch was made nationwide.

Benefits to Australia would be lesser because the population is much smaller, and full benefits will be achieved only if potassium-enriched salt was incorporated into food manufacturing processes as well as being used in the home. Nonetheless, a nationwide 10–15% reduction in cardiovascular events, comparable to that achieved in the Salt Substitute and Stroke Study, would be substantial. There are about 42 000 deaths per annum caused by cardiovascular disease in Australia and this would translate to 5000 premature deaths averted every year.

Switching to iodised and potassium-enriched salt is a low cost, high impact opportunity for rapidly and massively improving global health outcomes. There is clear potential to accrue large benefits in Australia.

There should be a population-wide recommendation for everyone to switch to a potassium-enriched salt unless there is a clear risk of hyperkalaemia. Supermarkets should replace their stocks with low cost potassium-enriched salt, and the food processing industry should switch to using potassium-enriched salt.

In contrast to prior failed sodium reduction efforts, the simplicity of the intervention and the joint benefits of sodium reduction and potassium supplementation provide a very high likelihood of success. Switching Australia’s, and the world’s, salt supply to potassium-enriched salt should be a priority.

Professor Bruce Neal is Executive Director of the George Institute, Australia, Professor of Medicine at UNSW Sydney, and Professor of Clinical Epidemiology at Imperial College London.

The statements or opinions expressed in this article reflect the views of the authors and do not necessarily represent the official policy of the AMA, the MJA or InSight+ unless so stated.

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