The first author of the study is Pekka Jousilahti, a research professor at the National Institute for Health and Welfare in Helsinki, Finland.
Sodium - which we mostly derive from the salt we eat - is key for a range of bodily functions, such as nerve function, muscle flexibility, and fluid balance.
In fact, due to the increased risk of high blood pressure and cardiovascular disease that is associated with a high intake of sodium, the American Heart Association (AHA) recommend reducing the daily consumption of dietary sodium to less than 1,500 milligrams (mg).
"In addition to CHD and stroke, heart failure is one of the major cardiovascular diseases in Europe and globally," Prof. Jousilahti adds, "but the role of high salt intake in its development is unknown."
Partly, the authors note, this is due to the difficulties of monitoring how much salt people consume on an individual level.
Studying salt intake and heart failure risk
To account for this methodological problem, Prof. Jousilahti and team used the so-called "24 hour sodium excretion" method, which is widely considered the most accurate technique for assessing salt intake.
The researchers examined the data available from the North Karelia Salt Study and the National FINRISK Study - both conducted in Finland between 1979 and 2002. The scientists randomly chose 4,630 men and women aged between 25 and 64 at the time of enrollment.
At baseline, the scientists gathered data using a self-administered questionnaire, in which the participants were asked about their health habits.
To assess salt intake, the researchers calculated 1 gram of ingested sodium as being the equivalent of 17.1 millimoles (mmol) of excreted sodium, as detected in the 24 hour urine sample.
The participants were clinically followed for nearly 12 years, during which time the researchers had access to their National Health Records.
Prof. Jousilahti and his team obtained information about the incidence of new heart failure and heart failure-related deaths from the Causes-of-Death Register, the Hospital Discharge Register, and the drug reimbursement records.
High salt intake doubles risk
During the study's overall period of follow-up, 121 men and women had new heart failure. After adjusting for potential confounders, the researchers found that "high salt intake increases the risk of [heart failure] markedly."
The study's lead author summarizes the findings, saying:
"People who consumed more than 13.7 grams of salt daily had a two times higher risk of heart failure compared to those consuming less than 6.8 grams. [...] The optimal daily salt intake is probably even lower than 6.8 grams. [...] This salt-related increase in heart failure risk was independent of blood pressure."
Prof. Pekka Jousilahti
"The World Health Organization [recommend] a maximum of 5 grams per day and the physiological need is 2 to 3 grams per day," the professor continues.
A teaspoon of salt roughly contains 5.8 grams.
"The heart does not like salt," Prof, Jousilahti says. However, he also concedes that more research is needed to confirm his and his team's findings: "Studies in larger, pooled population cohorts are needed to make more detailed estimations of the increased heart failure risk associated with consuming salt."