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UPDATED: November 29, 2021 at 4:00 p.m.

Researchers at the Harvard T.H. Chan School of Public Health found in a study published in the New England Journal of Medicine that consuming less sodium and more potassium is linked to lowering the risk of cardiovascular diseases.

Frank Hu, the chair of the Department of Nutrition at HSPH and a senior author of the study, said the project began after his co-author Yuan Ma, an epidemiologist at HSPH, received the American Heart Association Postdoctoral Fellowship Award, which has the goal of resolving a major “controversy” in the nutrition field.

Hu said that though studies have long confirmed the link between high sodium intake and poor cardiac health, there has been scientific debate over whether lowering sodium decreases the risk of cardiovascular disease.

“Not that many studies have looked at the link between sodium and cardiovascular disease directly,” he said. “It’s very difficult to do that type of study because you need a very large number of people, you have to follow them for years or even decades, and you need to have a very reliable measure of sodium intake.”

Such studies typically use a research method called “spot urine” samples, in which urine samples are collected every 24 hours, per the authors. These can be misleading, however, according to Ma, and only relying on daily samples has contributed to controversial findings in past studies.

“The total amount of sodium cannot be reflected in just a spot urine, which may be biased or inaccurate,” Hu said. “In this study we used multiple 24-hour urine samples to measure habitual sodium intake in more than 10,000 people, and then look at sodium intake levels and subsequent risk of cardiovascular disease, which includes heart disease or stroke.”

Ma and Hu collaborated with five cohorts in the United States, along with researchers at Groningen University in the Netherlands and experts from the United Kingdom and Canada in their data collection.

“This is basically teamwork and international collaboration,” Ma said.

Ma and Hu said they hope their research will allow for more effective public health policy surrounding sodium.

“Unfortunately, these controversial findings have largely impeded the implementation of the public health policy on reducing sodium intake,” Ma said. “This has very important public health implications. This issue needs to be clarified before they go further, [before] more actions can be taken on public health policies regarding sodium reduction.”

Ma also noted the importance of effective communication and transparency with the public that the study might provide.

“We feel that for us as researchers, we have the responsibility to deliver results that are from rigorous methods that we feel are reliable and not misleading for the public,” Ma said.

CORRECTION: November 29, 2021

A previous version of this article misquoted Frank Hu as saying the study measured habitual sodium intake in more than 100,000 people. In fact, it was more than 10,000 people.