Salt is at the center of a battle among government agencies and health advisers who can't agree on what is too much or too little for a healthy diet.
Four months after an Institute of Medicine report said reducing salt to the lowest recommended level doesn't improve health and may harm it, the U.S. Centers for Disease Control and Prevention said they disagree. In an article published in the American Journal of Hypertension, the CDC and New York City health officials said getting Americans to eat less salt remains a key objective with the potential to save thousands of lives.
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The IOM report stirred controversy after doctors and news organizations suggested the findings meant national efforts to cut salt consumption were unnecessary and potentially dangerous. The CDC, which commissioned the IOM report, the New York City Department of Health and others are now writing in to reiterate their commitment to lowering sodium consumption.
"We strongly believe that given the current high levels of sodium consumption and the preponderance of scientific evidence supporting lower consumption, sodium reduction strategies must remain at the top of the public health agenda," said New York City Health Commissioner Thomas Farley and his colleagues. "It is the shared responsibility of public health leaders, journalists, and government officials to get the message right: reducing sodium intake saves lives."
The IOM review analyzed studies from the past decade to see if sodium reduction prevented heart disease and death. While more sodium does increase heart disease risk, reducing it too much can also cause harm for some people, the report found.
At issue is the question of how low consumers should go when it comes to salt. The U.S. Department of Health and Human Services recommends no more than 2,300 milligrams a day in general, and 1,500 milligrams a day for anyone with hypertension and everyone who is black or older than 51. The high-risk subgroup accounts for roughly half of the U.S. population.
The CDC is committed to trying to get the U.S. population to those levels, down from the current average consumption of 3,400 milligrams, wrote CDC Director Thomas Frieden and his colleagues.
That goal may be dangerous, said Michael H. Alderman, the editor-in-chief of the American Journal of Hypertension, who pulled together eight reports and commentary that explored all angles of the debate. The relationship between heart disease and sodium "has a 'J' shape," with both low and high levels creating risk, he said in a telephone interview.
The original assumptions made sense, he said. Reducing sodium intake by 30 percent to 50 percent lowers blood pressure by a modest amount. Lowering blood pressure has been proven in numerous studies to protect the heart. Therefore, people assumed reducing sodium would protect the heart. The problem was the data didn't support the conclusion, he said.
"Lowering sodium to the extent required to lower blood pressure has a variety of other effects," including some that boost heart attacks, strokes and death, he said. "It's just not that simple. The message from the evidence is we don't know."
It looks like there is a broad range of sodium intake that's compatible with excellent health, he said. Getting too much or too little is a problem. More research is needed to clearly identify those levels, he said.
"Thirty years of looking hard to find evidence that people eating less than the recommended levels of sodium are better off, and not having found it, may give people pause to think maybe it isn't there," he said. "It's not that there is conflicting data. There is no data that suggests people eating less than 2,300 milligrams a day are better off."
Alderman said it's "incumbent on the CDC and others who support these recommendations to come up with evidence" that shows what levels of sodium are safe.
"Hypertension is my game," he said. "I'm interested in lowering blood pressure, of course. But what I'm really interested in is saving lives and preventing heart attacks and strokes."