While most health agencies advocate a low-sodium diet for heart health, a controversial new study out of the Population Health Research Institute (PHRI) of McMaster University and Hamilton Health Sciences in Canada has found that the opposite holds true— low salt intake may not be beneficial, and might actually increase the risk of cardiovascular disease (CVD) and death when compared to those who consumed an average amount of sodium.

The study, which is published in The Lancet, recruited 133,118 people across 49 countries. After measuring the sodium in their urine to estimate how much they consume on a daily basis, they followed these people across a median time period of 4.2 years and correlated their sodium levels to major CVD events (like heart disease and stroke) and mortality rates.

At the end of the study, they found that regardless of blood pressure level, lower sodium intake than the average Canadian consumes (less than 3,000 mg per day) was tied to a greater number of heart attacks, strokes, and deaths as compared to average intake (3,500 to 4,000 mg per day).

“These are extremely important findings for those who are suffering from high blood pressure,” said Andrew Mente, lead author of the study, a principal investigator of PHRI and an associate professor of clinical epidemiology and biostatistics at McMaster’s Michael G. DeGroote School of Medicine, in a statement.

“While our data highlights the importance of reducing high salt intake in people with hypertension, it does not support reducing salt intake to low levels. Our findings are important because they show that lowering sodium is best targeted at those with hypertension who also consume high sodium diets.”

Further, the study also found that a high sodium intake (6,000 mg per day) was only harmful to those with high blood pressure.

“Low sodium intake reduces blood pressure modestly, compared to average intake, but low sodium intake also has other effects, including adverse elevations of certain hormones which may outweigh any benefits. The key question is not whether blood pressure is lower with very low salt intake, instead it is whether it improves health,” said Mente.

The American Heart Association strikes back

Many health experts strongly disagree with the results of the study, with the American Heart Association leading the criticism.

“This is a flawed study and you shouldn’t use it to inform yourself about how you’re going to eat,” said Elliott Antman, M.D., associate dean for clinical/translational research at Harvard Medical School and senior physician in the Cardiovascular Division of Brigham and Women’s Hospital in Boston, in an AHA statement. “The AHA has reviewed the totality of the evidence and we continue to maintain that no more than 1,500 milligrams of sodium a day is best for ideal heart health.”

(1,500 milligrams, of course, is the recommendation for the average person, not including those working in extreme heat or with specific illnesses.)

Antman went on to point out that the methods of the study—namely, estimating daily salt intake based off of a single urine test at the start of the study—is likely a poor indicator of how much salt a person truly consumes. This is because urine does not reflect how much salt a person eats in the long-term, but rather how much they just ate.

“If we followed you for two years and made assumptions on whatever that first meal was, it just wouldn’t be accurate all along the way,” said Antman. “There are a lot of assumptions being made in this study, and the results are not reliable.”

“The link is proven between excess sodium and high blood pressure, and I find it worrisome that adoption of the authors’ recommendations may reverse the progress that has occurred in modifying dietary sodium intake and reducing the risk of high blood pressure and its effect on heart disease and stroke,” added Mark Creager, M.D., president of the American Heart Association and director of the Heart and Vascular Center at Dartmouth-Hitchcock Medical Center at Dartmouth College.

“Today’s widely accepted sodium recommendations are based on well-founded scientific research – and that’s what people should understand.”

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