It seems that barely a day goes by without new research emerging that shows the dangers of consuming too much salt. Used for centuries across the world to season, preserve and improve the flavour of food, the link between sodium chloride – the most common form of salt in the human diet – and high blood pressure, cardiovascular disease (CVD) and other major health risks have been well established.

One of the major studies to identify this link was the Intersalt study in 1997, which added significantly to the ever-growing body of research that suggests a habitual high salt intake is one of the quantitatively important, preventable mass exposures that causes the unfavourable population-wide blood pressure pattern, which is a major risk factor for epidemic cardiovascular disease. From this, food and health agencies have derived clear guidance for salt intake.

“Evidence to suggest a relationship with sodium and hypertension – and thus risk of CVD – has been around for a while,” says Janette Walton of the department of biological sciences at the Cork Institute of Technology. “The Food Standards Agency in the UK and the Food Safety Authority of Ireland have set target maximum population salt intakes of less than 6g per day in relation to hypertension and CVD risk, but intakes are currently well above this.”

The WHO estimates that the global average salt intake is 10.8g per day, more than double the organisation’s recommendation of less than 5g per day. The latest work by the WHO not only urges everyone to reduce dietary salt intake, but the recently launched WHO global report on sodium intake reduction will monitor the progress and identify the areas for action through implementing reduction policies and other measures within member states, across WHO regions and World Bank income groups.

“The Food Standards Agency in the UK and the Food Safety Authority of Ireland have set target maximum population salt intakes of less than 6g per day in relation to hypertension and CVD risk, but intakes are currently well above this.”

In the report, a sodium country score of one (the lowest level) to four (the highest level) will be allocated to each member state based on the level and effectiveness of sodium reduction policies and other measures. This will be used to estimate the impact of policy progress on population dietary sodium intake and cardiovascular disease.

The recommended daily intake of sodium salt.

“Unhealthy diets are a leading cause of death and disease globally, and excessive sodium intake is one of the main culprits,” said Dr Tedros Adhanom Ghebreyesus, WHO director-general at the launch. “This report shows that most countries are yet to adopt any mandatory sodium reduction policies, leaving their people at risk of heart attack, stroke, and other health problems.”

The potential of potassium

As well as CVD and hypertension, new risk factors appear to be emerging. A recent study by researchers at Vanke School of Public Health at Tsinghua University, Beijing and the Department of Epidemiology at Johns Hopkins University examined the impact of sodium and potassium – put forward as the healthier alternative to sodium – on the risk of cognitive decline in older people. The results showed high dietary sodium intake is associated with cognitive decline, while elevated levels of dietary potassium is linked with improved cognitive function.

A systemic review recently published in the Journal of Alzheimer’s Disease looked at 15 studies – one clinical trial, six cohorts and eight cross-sectional studies – and investigated the link between sodium intake, cognitive function and dementia risk. It found they reported mixed associations between sodium levels and cognition, nevertheless, the results of the only clinical trial showed lower sodium intake was associated with improved cognition over six months.

That link needs to be examined further, but the existing risks of CVD and hypertension are enough to merit serious action on sodium. After all, CVD – which includes ischaemic heart disease and strokes – kills more people each year than any other disease.

The appropriate response to these risks seems to be simple, just eat less salt. But controlling the daily intake of large populations is extremely difficult. Therefore, the current thinking seems to be that encouraging the substitution of salt based on potassium rather than sodium would be simpler and more beneficial to health outcomes.

A recent study led by Bruce Neal of the George Institute for Global Health, and professor of clinical epidemiology at Imperial College London, recorded a significant reduction in cardiovascular events in a population of more than 20,000 adult participants, many of whom had an existing history of stroke and/or hypertension. The results, published in 2021, show the rate of stroke was lower with the salt substitute than with regular salt – 29.14 events compared with 33.65 events per 1,000 person-years.

 “Though the human body does need a very small amount of sodium to function properly, most people nowadays consume too much,” Neal remarks. “Of all dietary risk factors, our current high salt intake is estimated to be responsible for most deaths and disability worldwide – meaning our excess salt consumption is more harmful to health than low fruits and vegetable intake or soft drink consumption, for example.”

“A gradual reduction in salt intake across the whole population, as recommended by the WHO, is achievable, affordable, and cost-effective,” he adds. “An example of a good substitute to regular table salt would be a low-sodium, high-potassium salt. While sodium raises blood pressure, potassium lowers it.”

Take it with a grain of salt

Walton’s recent work has looked closely at the balance between sodium and potassium in a healthy diet. Both minerals are vital to the healthy functioning of the human body, so the current argument is not about entirely replacing one with the other, rather achieving the right balance between the two. Given the high and widespread use of sodium-based salt, however, this could be the key area where substituting with potassium-based salts may have the biggest impact on health.

“My research has shown that sodium intake is above the recommended [guidelines] and potassium intake is below recommendations,” she remarks. “Following food-based dietary guidelines will help to balance this by increasing consumption of fresh foods including fruit and vegetables, milk and yoghurt, and fresh rather than processed meats.”

The ratio of sodium (Na) to potassium (K) intake is an important predictor of hypertension, so Walton investigated the Na:K ratio in adults with data from the Irish National Adult Nutrition Survey (2008–2010), which collected spot urine samples and dietary data in a nationally representative sample of Irish adults. The findings showed sodium intake exceeded target maximum population goals for all gender and age groups.

“Reducing salt intake at population level from low nutrient dense foods is in keeping with public health advice linked mainly to hypertension and CVD),” says Walton. “Substituting sodium for potassium in salt will increase potassium levels whilst decreasing sodium levels. It is certainly one strategy, but a reduction in low nutrient dense foods in parallel with an increase in high nutrient dense foods – including fruit and vegetables – is also necessary.”

No substitute for a healthy diet

Potassium-based salt certainly seems to be one of the most useful weapons in the battle against excess sodium intake, but it cannot win the war all by itself. This is partly because reworking the global supply chain to bring potassium-based salt to supermarket shelves at the same price as traditional table salt will require time, effort and the willingness of the food industry to make such a big change.

In the meantime, Walton and other researchers suggest that a healthy diet should contain plenty of potassium-rich foods. Bananas, avocados, dried and fresh fruits, leafy greens, potatoes, milk, yoghurt and fresh meat can all help people to achieve a lower Na:K ratio. On the other hand, breads, cured and processed meats, butters and fat spreads have the opposite effect.

The WHO, meanwhile, is calling on countries to implement its ‘best buys’ for sodium reduction – reformulating foods to contain less salt; establishing public food procurement policies to limit salt or sodium rich foods in public institutions such as hospitals, schools, workplaces and nursing homes; using front-of-package labelling that helps consumers select products lower in sodium; and engaging in behaviour change communication through mass media campaigns to reduce salt or sodium consumption. It is also calling on food manufacturers to implement the WHO benchmarks for sodium content in food.

“My research has shown that sodium intake is above the recommended [guidelines] and potassium intake is below recommendations.”

“I think that consumers are aware of the sodium message,” says Walton. “They may not be as aware of the potassium message, but most people are already aware of the message to consume at least five-a-day of fruit and vegetables. Behaviour change is extremely complex, and awareness and education [form] only one aspect of it.”

The estimated global average intake of salt per day.

“Awareness is extremely important,” she adds. “So clear labelling is definitely important, but awareness doesn’t always lead to behaviour change.” Building a healthier world is no simple task, but the latest research has at least confirmed the tools that we can use to address the risk of CVD and cognitive decline through dietary changes.