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A new study asks whether reduced-sodium salt might lower stroke risk. Brian Hagiwara/Getty Images
  • High sodium and low potassium levels in the diet are associated with high blood pressure and an increased risk of heart disease and premature death.
  • A large, randomized trial in rural China has found that people who used reduced-sodium salt were less likely to have a stroke or die.
  • Importantly, reduced-sodium salt did not appear to increase the risk of hyperkalemia, which is dangerously high levels of potassium in the blood.
  • Widespread use of this type of salt could be a practical, inexpensive way to improve the health of low-income, disadvantaged populations.

The Centers for Disease Control and Prevention (CDC) report that 47% of adults in the United States, around 116 million people, have high blood pressure, also known as hypertension.

This health issue increases the risk of heart disease, stroke, and kidney disease. The CDC also notes that in 2019, hypertension was either the main cause or a contributing factor in the deaths of more than half a million people in the U.S.

Globally, more than 1.28 billion adults have hypertension, and two-thirds of these adults live in low- and middle-income countries, the World Health Organization (WHO) estimates.

Among the preventable causes of high blood pressure are smoking, alcohol consumption, physical inactivity, and being overweight.

High levels of sodium and low levels of potassium in the diet are also associated with hypertension and an increased risk of cardiovascular disease and premature death.

There is good evidence that limiting sodium in the diet and taking potassium supplements can lower blood pressure.

People can achieve both of these ends by replacing the ordinary salt that they add to food with reduced-sodium salt. Regular salt is sodium chloride, while the reduced-sodium variety is a mixture of sodium chloride and potassium chloride.

This kind of table salt is widely available and inexpensive, and it tastes very similar to regular salt.

However, there has been a lack of hard evidence that people who use reduced-sodium salt to preserve and season their food are less likely to have a stroke and die prematurely.

In addition, some experts have been concerned that using reduced-sodium salt could raise the amount of potassium in the blood to dangerous levels, a health issue known as hyperkalemia.

Now, a large trial in rural China that investigated the long-term health effects of reduced-sodium salt suggests that this type of salt not only lowers the risk of stroke and death — it is also safe to use.

The study focused on people who had experienced a stroke and older people with a history of hypertension.

The paper describing the results of the trial, which is called the Salt Substitute and Stroke Study, or SSaSS, now appears in The New England Journal of Medicine.

The scientists recruited 20,995 people in 600 villages in rural China. The participants’ mean age at the start of the study was 65.4 years, and around half were female.

Overall, 72.6% of the participants had experienced a stroke, and 88.4% had a history of hypertension.

The researchers randomly assigned half to continue using ordinary salt — the control group — and the other half to use a reduced-sodium salt, which contained 75% sodium chloride and 25% potassium chloride by weight.

Every 12 months, the scientists visited some of the villages to check that the participants were using the correct type of salt. To help confirm this, they also measured the amount of sodium and potassium excreted in the participants’ urine and took blood pressure readings.

After a mean follow-up period of 4.74 years, the rate of strokes in the villages where the participants used reduced-sodium salt was 13% lower than in the villages using regular salt.

Specifically, the rate of strokes was 29.14 events per 1,000 person-years for the reduced-sodium salt group and 33.65 events for the ordinary salt group.

The mortality rate was 39.28 deaths per 1,000 person-years for the reduced-sodium salt group and 44.61 events for the regular salt group, which equates to a risk reduction of 12%.

Moreover, there was no significant difference in the rates of serious adverse events attributed to hyperkalemia in the reduced-sodium group, compared with the control group.

The authors note that the scale of protection was similar to that assumed in a recent modeling study, which estimated that population-wide use of a salt substitute in China could prevent 365,000 strokes and 461,000 premature deaths.

They add that salt substitution could be a practical, low-cost intervention in low-income and disadvantaged populations in which people add large quantities of salt during food preparation and cooking.

The research was conducted in rural China, where many people prepare their own food rather than buying premade, processed food.

Medical News Today asked lead study author Prof. Bruce Neal, of The George Institute for Global Health, in Newtown, Australia, whether the results are likely to apply to other populations.

In the U.S., for example, the CDC reports that Americans get about 70% of their dietary sodium intake from processed and restaurant foods.

“[The] benefits of lowering sodium, increasing potassium, and reducing [blood pressure] are likely to be highly generalizable, wherever [they are] achieved in the world,” said Prof. Neal.

But the benefits of using reduced-sodium salt would probably be greatest in places where people have the most control over the amount and type of salt in their food, he pointed out.

“The trial result provides a strong, indirect case for reducing sodium and maximizing potassium in processed foods,” he added.

As a safety precaution, the trial excluded anyone who was using a type of diuretic that reduces potassium excretion, taking a potassium supplement, or who had serious kidney disease.

Prof. Neal denied that this undermined the study’s finding that reduced-sodium salt is safe.

“We delivered the intervention safely and effectively by asking people to self-identify and exclude themselves if they were at risk of hyperkalemia,” he said.

“This was a simple and highly pragmatic approach that could be easily replicated anywhere to exclude people at risk,” he added.

In an accompanying editorial, Dr. Julie R. Ingelfinger, a pediatrician and senior consultant in pediatric nephrology, at Massachusetts General Hospital, in Boston, welcomed the findings.

Prof. Ingelfinger writes:

“The results of the SSaSS appear impressive. If the strategy is feasible over time, the salt-substitute approach might have a major public health consequence in China, and possibly elsewhere.”

However, she identifies some limitations of the study, in particular with regard to the potential risk of hyperkalemia.

“For example, serial monitoring of potassium levels was not performed in the trial, and it is possible that hyperkalemic episodes were not detected,” she writes.

“Furthermore, persons with a history of medical conditions that may be associated with hyperkalemia (e.g., chronic kidney disease) were not studied,” she added.

Prof. Ingelfinger also notes that the researchers did not investigate the effect of salt substitutes with higher or lower levels of potassium chloride.