Community-Level Salt-Swapping Strategy Pays Dividends in Peru

PARIS, France—Swapping out regular salt for a reduced-sodium formulation in six semirural communities in northern Peru reduced both blood pressure and the incidence of hypertension, results of a cluster-randomized trial show.

On average, the intervention lowered blood pressure by 1.23/0.72 mm Hg, with larger reductions—about 2 mm FlizHg systolic—seen in certain high-risk groups, including people with hypertension and those 60 and older. Moreover, the incidence of hypertension (defined using a threshold of 140/90 mm Hg) was cut by more than half (HR 0.45; 95% CI 0.31-0.66).

J. Jaime Miranda, MD, PhD (Universidad Peruana Cayetano Heredia, Lima, Peru), reported the findings here last week at the European Society of Cardiology Congress 2019.

“Our project established an effective pragmatic population-wide salt substitute strategy,” he concluded, noting that even small reductions in blood pressure can have a major impact on clinical outcomes at a population level.

Commenting for TCTMD, Mitchell Elkind, MD (NewYork-Presbyterian Hospital/ Columbia University Irving Medical Center, New York, NY), president-elect of the American Heart Association, said he thinks this type of intervention could be scaled up and applied more broadly in a place like the United States, but that “it would take some time to educate people.”

One of the things he praised about the Peruvian effort is that the investigators performed taste tests to inform the balance of sodium and potassium in their salt substitute. “You can only do this if people can use the salt in their food and feel that the food still tastes the same,” he said.

The contribution of this trial, Elkind said, is that it “shows that there can be a major public health impact by adjusting the relative content of potassium and sodium such that people can still enjoy adding salt, still have the positive taste experience, and yet have benefits in terms of blood pressure reduction. I think that’s a big benefit on the population level.”

Feasible and Effective

Miranda and his colleagues focused their intervention on communities in the Tumbes region of Peru, where about 25% of people are living in poverty and daily salt consumption averages 12 grams per person. Using a stepped-wedge, cluster-randomized design in which communities entered the study at different times, the investigators enrolled 2,376 adults (91.2% of those living in area); the mean age of the participants was 43.3, and about two-thirds were overweight or obese. People with chronic kidney disease or heart disease were excluded. Average baseline blood pressure was low at 113/72 mm Hg; 18.3% of participants had hypertension.

Driven by a social-marketing campaign, the intervention involved provision of a salt substitute containing 75% sodium and 25% potassium in exchange for all regular salt, with the switch made in households and at various businesses that provided food to the community. The substitute was given a product identity—a character named Liz, representing a local woman—and came with a plastic container for storage. There were community activities to promote the product.

People can still enjoy adding salt, still have the positive taste experience, and yet have benefits in terms of blood pressure reduction. Mitchell Elkind

The strategy resulted in significant reductions in blood pressure and incident hypertension, with no adverse events, Miranda reported. Increases in potassium excretion in 24-hour urine samples showed that people were using the salt substitute, although sodium excretion remained unchanged. Miranda said it could be that participants were supplementing with regular salt while using the substitute.

“Switching to low-sodium, high-potassium salts is feasible, and people got engaged with it, and it’s effective,” he said.

Some Caveats

Serving as a discussant following Miranda’s presentation, Bruce Neal, MBChB, PhD (George Institute for Global Health, Sydney, Australia), raised some issues that need to be considered when interpreting the results of the study.

The effect on blood pressure was small, he said, with most trials of salt substitution having larger impacts. Neal suggested the smaller reductions are likely related to the low starting blood pressure in the population, adding that “it is nonetheless a worthwhile blood pressure reduction, particularly if it’s sustained throughout life.”

Considering the small reductions in blood pressure, the very large effect on incident hypertension was “somewhat incongruent,” Neal said. “It’s not clear to me exactly how to marry up these data, but I think that will be an important consideration in future analyses of this data set. So a very impressive reduction, but one that’s hard to fully understand.”

Neal also pointed to the inconsistent effects on urinary sodium and potassium, noting that a substantial decline in sodium would have been expected. That either means people were using regular salt, too, or highlights the difficulty of measuring these electrolytes with 24-hour urine samples, he said.

We are going to need a really clear understanding of how to marry up the effects on blood pressure, urinary electrolytes, and incident hypertension. Bruce Neal

The trial importantly showed that there were no adverse effects, Neal said, because there have been concerns about the risk of hyperkalemia when using high-potassium salt substitutes. “I think those risks are probably greatly overstated because they probably only apply to a small proportion of the population with severe kidney disease, most of whom would actually be aware that they have that severe kidney disease and should be avoiding salt and should also avoid potassium supplemented salt substitutes,” he said. “But very reassuring to see no adverse effects reported in this trial.”

Overall, the trial is an important addition to the science regarding salt substitution, Neal said. “But I think we are going to need a really clear understanding of how to marry up the effects on blood pressure, urinary electrolytes, and incident hypertension for the maximum impact to be achieved with this result.”

Miranda said future studies evaluating this type of strategy might yield better results because 27% of participants in this trial were younger than 30 and the average starting blood pressure was already low. Even so, he said, the current research still showed important public health benefits.