Switching from regular salt to a low-sodium salt substitute has major public health benefits, including a reduction in stroke, cardiovascular events, and death, a new landmark study shows.
The Salt Substitute and Stroke Study (SSaSS) was conducted in 21,000 people with a history of stroke or high blood pressure in rural China, with half of them using a lower-sodium salt substitute instead of regular salt.
Results showed that after 5 years, those using the salt substitute had a 14% reduction in stroke, a 13% reduction in major cardiovascular events, and a 12% reduction in death. These benefits were achieved without any apparent adverse effects.
The trial was presented by Bruce Neal, MB, George Institute for Global Health, Sydney, Australia, on August 29 at the virtual European Society of Cardiology (ESC) Congress 2021. They were simultaneously published online in the New England Journal of Medicine (NEJM).
“This is one of the largest dietary intervention trials ever conducted and has shown very clear evidence of protection against stroke, cardiovascular events, and premature death, with no adverse effects with a very simple and low-cost intervention,” Neal concluded. “This is a very easy thing to work into the diet. You just replace regular salt with a substitute that looks and tastes almost identical,” he added.
Addressing the issue of whether these results are generalizable to other populations, Neal said, “We believe the results are relevant to everyone who eats salt.”
“The way the body manages sodium and potassium and their association with blood pressure is highly consistent across different populations,” he said. “Almost everyone, with the exception of a few people with serious kidney disease, should be avoiding salt or switching to a salt substitute and expect to see some benefit of this.”
Commentators at the ESC presentation lauded the study as “magnificent,” with “extraordinary” results and “very powerful implications.”
Designated discussant, hypertension expert Bryan Williams, MD, University College London, United Kingdom, said the SSaSS was “probably the most important study with regards to public health that we will see.” He described the reductions in stroke, cardiovascular events, and death as “extraordinary for such a simple intervention.”
Williams added: “Those who have doubted the benefits of salt restriction must now admit they were wrong. The debate stops here. The data are in. Global health interventions to implement these findings must now begin.”
He also highlighted the large number of events in the trial. “This was a large, pragmatic, long-duration study in a high-risk population, and with 5000 cardiovascular events it gives enormous power to show benefits.”
Chair of the ESC session, Barbara Casadei, MD, DPhil, John Radcliffe Hospital, Oxford, United Kingdom, said the SSaSS “will change the way we think about salt and be remembered for years to come.”
Noting that the benefits were seen in all subgroups across the study, Bertram Pitt, MD, University of Michigan School of Medicine, Ann Arbor, was particularly excited about the stroke reduction seen in patients with diabetes, noting that several recent trials of new diabetes drugs have not managed to show a reduction in stroke.
“For patients with diabetes, this is a really important intervention,” he stated.
However, an editorial accompanying the NEJM publication gave a somewhat less enthusiastic response to the study than the ESC commentators.
Julie R. Ingelfinger, MD, deputy editor of the journal, points out that serial monitoring of potassium levels was not performed in the trial, so it is possible that hyperkalemic episodes were not detected, and persons with a history of medical conditions that may be associated with hyperkalemia were not studied.
She also notes that because the salt substitute was distributed to families, it would have been instructive to have data on the household members without risk factors, but no such data were obtained.
“Overall, the SSaSS provides some intriguing hints, but wider effectiveness is hard to predict, given limited generalizability,” she concludes.
The SSaSS was an open-label, cluster-randomized trial involving 20,995 people from 600 villages in rural China who had a history of stroke or were 60 years of age or older and had uncontrolled hypertension. Patients with a history of severe kidney disease and those taking potassium supplements or potassium-sparing diuretics were excluded.
They were randomly assigned in a 1:1 ratio to the intervention group, in which the participants used a salt substitute (approximately 75% sodium chloride and 25% potassium chloride), or to the control group, in which the participants continued to use regular salt (100% sodium chloride).
Results showed that after a mean follow-up of 4.74 years, systolic blood pressure was reduced by 3.3 mm Hg in the salt substitute group.
The rate of stroke, the primary endpoint, was 29.14 events per 1000 person-years in the salt substitute group vs 33.65 events per 1000 person-years with regular salt (rate ratio, 0.86; 95% CI, 0.77 – 0.96; P = .006).
The rates of major cardiovascular events were 49.09 events per 1000 person-years in the salt substitute group vs 56.29 events per 1000 person-years in those using regular salt (rate ratio, 0.87; 95% CI, 0.80 – 0.94; P < .001).
And the rate of death was 39.28 events per 1000 person-years with the salt substitute vs 44.61 events per 1000 person-years with regular salt (rate ratio, 0.88; 95% CI, 0.82 – 0.95; P < .001).
The rate of serious adverse events attributed to hyperkalemia was not significantly higher with the salt substitute than with regular salt (3.35 events vs. 3.30 events per 1000 person-years; rate ratio, 1.04; 95% CI, 0.80 – 1.37; P = .76).
Neal reported that 7% to 8% of the control group started using salt substitute over the study period, so these results have likely underestimated the true effect of switching to a salt substitute product.
Noting that about 10 million cardiovascular events occur each year in China, he said the study results suggested that using salt substitute instead of regular salt could prevent about 10% of these events.
Food Manufacturers Must Make Changes
Neal acknowledged that a limitation of the study was the fact it was conducted in a single country, which would raise issues of generalizability. But he believes the results are generalizable to other populations.
Those who would get the most benefit from switching to a salt substitute are those who consume large amounts of discretionary salt — salt added at home at the time of cooking for preservation of food or seasoning. “This is salt that is easy to replace with salt substitute,” Neal noted.
“There are more than 5 billion people in the world that consume more than 50% of their salt intake as discretionary salt — mainly in the developing world. These people would expect to get significant health benefits from a switch to salt substitute.”
He pointed out that salt substitute is low cost and is easy to manufacture. “Salt substitutes cost around 50% more than regular salt, but this translates into just a dollar or two per person per year to make the switch.”
Neal believes the results also apply to higher-income countries but must be implemented by governments and food manufactures, as most salt in these countries comes from processed foods.
“This study provides strong evidence to take to the food industry,” he concluded. “We would like to see food manufacturers switch to using salt substitute and for salt substitute products to be widely available on supermarket shelves. We also urge governments to take action to promote use of salt substitutes over regular salt. This could take the form of taxing regular salt or subsidies for use of salt substitutes.”
The SSaSS was supported by grants from the National Health and Medical Research Council of Australia. Neal reports no disclosures. Ingelfinger is employed by the New England Journal of Medicine as deputy editor.
European Society of Cardiology (ESC) Congress 2021. Presented August 29, 2021.
N Engl J Med. Published online August 29, 2021. Abstract, Editorial