In the kitchen, salt almost feels like cheating. Adding just the right dash of salt instantly enhances the flavor of almost any savory dish – but there's a definite downside to this cheap and plentiful ingredient.

Put simply, too much salt is bad for you. More specifically, too much sodium is bad for you, and sodium is one of the two primary elements that make up salt (aka the chemical compound sodium chloride).

Much prior research has investigated the links between excess levels of dietary sodium and health issues – such as increased risk of cardiovascular disease.

At the same time, other studies have plotted the health impacts of insufficient potassium in people's diets, which also has a negative effect on blood pressure.

As it happens, one product – commonly available in many supermarkets – can mitigate both these problems at the same time: salt substitutes that are designed to taste just like salt, but feature reduced levels of sodium and added amounts of potassium.

Despite the promise of salt substitutes, however, there's been a lack of large clinical trials measuring their impact on stroke, heart disease, and death, so questions remain about how effective they are.

Now, a giant study conducted in China seems to suggest pretty much everybody would benefit from making the switch.

"Almost everyone in the world eats more salt than they should," says clinical epidemiologist Bruce Neal from the George Institute for Global Health in Australia.

"If salt was switched for salt substitute worldwide, there would be several million premature deaths prevented every year."

In the study, Neal and his team examined over 20,000 villagers from rural areas in China, recruiting participants with a history of stroke or poor blood pressure. The people came from 600 villages in total, with an average age of about 65 at the outset of the trial.

In the experiment, half the participants were given a free supply of salt substitute to use for the course of the trial (designed as a five-year experiment, but slightly affected by the COVID-19 pandemic).

The salt substitute they were given featured less sodium and added potassium, and they were encouraged to use it more sparingly than they usually used salt, in order to maximize their overall sodium reduction.

Meanwhile, the other half of the villagers acted as a control group, and continued to use salt in their cooking and food preparation as they always had.

At the end of the study, there was a marked contrast in the health outcomes of these two groups.

Overall, roughly five years after the experiment had begun, more than 4,000 of the participants had died, with more than 3,000 experiencing a stroke, and over 5,000 having some kind of major cardiovascular event – sad and unfortunate outcomes, but not unexpected given their age and health at the outset of the trial.

Amongst the results, however, the salt substitute group was significantly less likely to experience strokes compared with the regular salt consumers (29.14 events vs. 33.65 events per 1,000 person-years), as well as lower chances of major cardiovascular events (49.09 events vs. 56.29 events), and death (39.28 events vs. 44.61 events).

The researchers say their results effectively confirm previous modelling in China, which suggested salt substitutions conducted on a national level could save the lives of an estimated 460,000 people every year, simply by preventing early deaths linked to the health effects of excessive sodium consumption.

By extension – and this part is hypothetical – the researchers suggest the same simple substitution would save millions of lives annually, if people worldwide made the switch from regular salt to its healthier, slightly tweaked alternative.

One potential barrier to seeing these protective effects could be due to the different ways food is made in different countries.

"In rural villages in China … processed food is not generally used; dietary sodium chloride is added during food preparation within each household," pediatrician Julie R. Ingelfinger from Massachusetts General Hospital, who wasn't involved with the study, explains in a commentary on the research.

"In contrast, in much of the world, commercial food preservation adds much sodium chloride to the diet, and the use of salt substitutes would not fully account for the majority of salt intake."

One answer could be substituting salt not just in the domestic kitchen, but in the industrial kitchen too, where commercially manufactured processed food is made.

In terms of cost, there's not that much difference the researchers say, with salt substitute costing about 50 percent more – but given how cheap regular salt is (about US$1.08 in China for a kilogram), and how little is generally needed in cooking, making the substitution is fairly affordable, especially given the benefits.

"While salt substitutes are a bit more expensive than regular salt, they're still very low-cost – just a few dollars a year to make the switch," Neal says.

"This is quite simply the single most worthwhile piece of research I've ever been involved with."

The findings are reported in The NEJM.