An unusual medical brawl erupted on Tuesday when the influential Institute of Medicine issued a report questioning the basis of years of advice for Americans to cut their salt intake in half.
The Institute, which advises the federal government on medical issues, concluded that the studies have answered the question poorly. A panel of experts looked at studies showing the medical effects of eating too much salt, as well as at studies that have been used to suggest that some people may suffer form eating too little salt.
Its finding: There’s enough evidence to support advising Americans to keep sodium to 2,300 milligrams a day or less, but there’s not enough to support the current, lower target of 1,500 milligrams a day.
“There is evidence to lower excessive salt intake,” Dr. Brian Strom, a professor of medicine, epidemiology and biostatistics at the University of Pennsylvania, who chaired the panel, told reporters.
There is also good evidence that lowering intake to around 2,300 milligrams a day decreased the risk of heart disease,” Strom said. But he said that the evidence was absent to support recommendations of taking it as low as 1,500 milligrams a day. And, he said, there were some studies suggesting this could harm some people -- although those studies are also flawed.
This infuriated the American Heart Association.
“While the American Heart Association commends the IOM for taking on the challenging topic of sodium consumption, we disagree with key conclusions,” Heart Association CEO Nancy Brown said in a statement.
“The report is missing a critical component -- a comprehensive review of well-established evidence which links too much sodium to high blood pressure and heart disease.”
The Institute agrees that Americans eat far too much salt -- more than 3,400 milligrams a day on average. Most is “hidden” salt, in processed foods such as bread and cereal, restaurant meals and especially fast food.
And studies clearly show that salt raises blood pressure and that cutting salt can lower blood pressure. High blood pressure damages blood vessels and can lead to stroke, kidney failure and heart failure.
“We knew about all this data and it didn’t change our thinking,” said Dr. Elliott Antman of Brigham and Women’s Hospital and Harvard Medical School . “We have to take the evidence that we have -- which is strong,” added Antman, a spokesman for the American Heart Association.
Several studies have suggested that about a quarter of Americans are salt-sensitive -- that their blood pressure is directly and immediately affected by how much salt they eat. But this doesn’t mean that the other 75 percent can pile on the salt with impunity, Antman said.
“About 90 percent of the population will ultimately develop hypertension as they age,” he said. “Part of this is almost certainly from years of eating too much salt, he added. Eating too much salt can also affect kidney function, he said.
“An aggressive reduction in sodium is the way to go,” he said.
Strom would not be drawn into an argument. “What we are saying is the available data is not consistent on outcomes,” he said. “We are not saying that one shouldn’t be lowering excessive salt intake in the general population,” he added. “There is simply a lack of data showing it is beneficial.”
And, he said, it is not up to the panel to set a target. “It’s not that we are against (a target intake of) 1,500 milligrams,” he said. “The data are not consistent.”
The trouble with trying to measure salt intake is that it’s very hard to separate out salt from the rest of the ingredients in food, said Antman.
A truly scientifically rigorous study would randomly assign people to eat diffferent amounts of salt daily and watch to see what kind of diseases they develop -- something that would be difficult to set up, police and also difficult to defend, ethically.
Antman says most Americans get their salt from prepared foods and from restaurants, not from at-home, scratch cooking. What’s needed, he said, is more encouragement for restaurants and food companies to lower sodium content of food.
The food industry argues that Americans have a taste for salt and they won’t buy products that are salt-free. Antman agrees that it’s hard. “We are used to a high sodium content in our food,” he said.
“But the data say that in just two to three weeks you can train person’s taste buds to become accustomed to a lower sodium content in food.”
The Center for Science in the Public Interest piled on, too.
"What the committee failed to emphasize is that most Americans are deep in the red zone, consuming 3,500 to 4,000 milligrams of sodium a day,' the group, which publicizes calorie counts and other food risks, said in a statement.
"It's clear that those excessive levels increase the risk of high blood pressure, heart attacks, and strokes. Whether we aim for 2,300 or 1,500 milligrams a day is irrelevant until we move down out of the red zone. At restaurants, you can get roughly 2,000 milligrams of sodium from just one burrito, a single-serve pizza, or an order of kung pao chicken, and at least 1,000 milligrams from a typical sandwich or burger."
The Centers for Disease Control and Prevention has a widget on salt intake here.