By Anne Harding
People who eat more sodium and less potassium may die sooner of heart or other problems than people who consume the opposite, a large, 15-year-study has found.
The study of more than 12,000 Americans provides more ammunition to health advocates who say that slashing salt intake will save lives. But not everyone is convinced, as some research is contradictory.
In the new study, men consumed an average of 4,323 milligrams of sodium a day, while women took in 2,918 milligrams.
The American Heart Association recommends people limit their sodium intake to 1,500 milligrams a day or less.
The group with the highest sodium-to-potassium ratio had a mortality risk about 50% higher during the study than the group with the lowest, according to the report by Elena V. Kuklina, M.D., and colleagues at the Centers for Disease Control and Prevention (CDC), Emory University, and the Harvard School of Public Health. The research was published Monday in the Archives of Internal Medicine.
A diet rich in fruits and vegetables is naturally low in sodium and high in potassium. Good potassium sources include bananas, baked potatoes, and raisins. In contrast, a diet of processed foods tends to be the opposite — it contains more sodium and less potassium, says Kuklina, a nutritional epidemiologist at the CDC.
“We probably should take into account the whole diet and take a more comprehensive look,” she says. “Looking at a single micronutrient, we might just miss the whole picture.”
Because most of the sodium people in the developed world consume comes from processed food, there has been a movement to get the food industry to reduce the amount of salt it adds to products.
In 2010, the Institute of Medicine recommended that the Food and Drug Administration regulate sodium in food. And the National Salt Reduction Initiative is a partnership of organizations — including major food companies — that aims to cut sodium in processed foods by 25% by 2014.
“We now have 28 companies who have committed to reducing the salt levels in at least one of their categories of products,” says Thomas A. Farley, M.D., of the New York City Department of Health and Mental Hygiene and coauthor of an editorial accompanying Kuklina’s study.
It’s the easiest way to reduce sodium intake, says Graham MacGregor, chairman of World Action on Salt and Health (WASH) and a professor of cardiovascular medicine at the Wolfson Institute of Preventive Medicine, in London.
The UK started doing just that in 2006, requiring companies to cut salt content by 25 to 30%. By 2008, according to MacGregor, sodium intake had fallen by 10%.
“It’s a very large study…and it clearly shows what we’d expect it to show, that eating too much sodium is harmful and eating too little potassium is harmful,” he says.
WASH is a global group established in 2005 with the aim of improving people’s health by reducing salt intake.
But the case isn’t quite closed, some say. For example, a report this May in the Journal of the American Medical Association found that while healthy men and women who ate more sodium than average weren’t at higher risk of dying of heart disease or stroke, cardiovascular mortality was 56% higher for people who ate the least sodium. The eight-year study included 3,681 European men and women age 60 or younger who did not have hypertension.
“It’s confusing,” says Michael Alderman, M.D., a professor of medicine and population health at the Albert Einstein College of Medicine, in the Bronx, and editor of the American Journal of Hypertension.
While some people with hypertension do need to reduce their sodium intake, Alderman says, reducing the sodium intake of the entire population could be harmful.
And an analysis of the evidence published in the Cochrane Review in July suggested that there isn’t strong evidence that people who cut back on salt will reap heart-health benefits. But it did say that a population-wide reduction might help.
“These findings should not be misinterpreted as showing that salt reduction will not save lives. There was insufficient evidence to make this judgment,” the author wrote. “Giving advice to reduce salt is a weak method of reducing salt intake in the population. Reducing hidden salt in processed foods, including bread, would likely have a bigger impact on blood pressure levels and on cardiovascular disease.”
Farley says concerns about the risks of salt reduction are unfounded.
“There are populations around the world who take in much, much less sodium than we do and they maintain lower blood pressure throughout their lives, so I’m not concerned about that,” he says. “The easiest way for people to think about it is they should be taking in less sodium and more potassium.”
As far as the JAMA study is concerned, Farley says, “I would consider that an outlier.”