Scientists: Salt Not That Bad For Health After All

Wednesday, April 08, 2015
Washington — For years, the federal government has advised Americans that they are eating too much salt, and that this excess contributes yearly to the deaths of tens of thousands of people.

But unknown to many shoppers urged to buy foods that are “low-sodium” and “low-salt,” this long-standing warning has come under assault by scientists who say that the typical American’s salt consumption is without risk.

Moreover, according to studies published in recent years by pillars of the medical community, the low levels of salt recommended by the government may actually be dangerous.

“There is no longer any valid basis for the current salt guidelines,” said Andrew Mente, a professor at McMaster University in Ontario, who was one of the researchers involved in a major study published last year by the New England Journal of Medicine. “So why are we still scaring people about salt?”

But the debate over dietary salt is among the most contentious in the field of nutrition, and other scientists, including the leadership of the American Heart Association, continue to support the decades-old warning.

The result is that as the federal government prepares its influential Dietary Guidelines for 2015, bureaucrats confront a dilemma: They must either retract one of their oldest dietary commandments — or overlook these prominent new doubts.

The U.S. Dietary Guidelines cover an array of nutritional issues, including cholesterol, fat and sugars. They have broad effects on American menus, shaping school lunches, guiding advertisers and serving as a touchstone for reams of diet advice.

Dennis Bier, a professor at Baylor College of Medicine in Houston, said that as the editor of the American Journal of Clinical Nutrition, he has been trying to stay neutral in what he considers the “hot buttonest” of topics.

“When you are making recommendations for 300 million people, you have to be concerned about any data that suggests harm,” Bier said.

A spokesperson for the Department of Health and Human Services said that the federal guidelines will consider comments from the public and the advice of its science panel. That panel, the Dietary Guidelines Advisory Committee, in February generally reaffirmed the current salt warning.

No matter what the government comes up with on salt, Americans may be left confused.

There is one area of consensus: Both sides agree that consuming too much salt, especially for people with high blood pressure, can be dangerous.

The critical disagreement concerns how to define “too much.”

Under the current dietary guidelines, too much is more than 2,300 milligrams of sodium per day — the amount of sodium in a teaspoon of salt. (For people over 50 and for African-Americans, the recommended intake is even lower — 1,500 milligrams per day.)

If the U.S. salt warnings are correct, Americans are indeed endangering themselves on a massive scale. Americans typically go way over the limit, ingesting about 3,500 milligrams per day.

If the skeptics are correct, on the other hand, most Americans are fine. In this camp’s view, a typical healthy person can consume as much as 6,000 milligrams per day without significantly raising health risks. But consuming too little — somewhere below 3,000 milligrams — raises health risks, they say.

To understand how divided scientists are on salt, consider that even authorities with the American Heart Association, one of the organizations promoting the current salt limits, don’t agree.

“The totality of the evidence strongly suggests that Americans should be lowering their sodium intake,” said Elliott Antman, president of the American Heart Association. “Everyone agrees that current sodium intake is too high.”

This is the long-established view. It is based on the observation that, in some people, reducing salt consumption can lower blood pressure. Because high blood pressure is common and raises the risk of cardiovascular troubles, strict salt limits will benefit society, according to this view.

None of this is persuasive to people such as Suzanne Oparil, a former president of the American Heart Association.

For one thing, the blood pressure reductions that come from avoiding salt are relatively small on average, because individuals vary widely in their reactions. (An average person who reduces his or her salt intake from median levels to the U.S. recommended levels may see a drop in blood pressure from 120/80 to 118/79, according to American Heart Association figures.)

“The current (salt) guidelines are based on almost nothing,” said Oparil, a distinguished professor of medicine at the University of Alabama at Birmingham. “Some people really want to hang onto this belief system on salt. But they are ignoring the evidence.”

How could something as simple as salt stymie scientists for so long?

The answer is that, despite the dietary claims that get made for all kinds of foods, actually substantiating how eating influences human health is notoriously difficult.

While the diets and lifestyles of test animals are easily controlled, humans and their whims introduce an array of murky variables, making people less than ideal subjects for what scientists call randomized controlled trials, their preferred form of research. This is especially true when these experiments go on for years, as diet research often does.

In the absence of such experiments, scientists are forced to consider lesser types of evidence. And in recent years, the debate appears to have tilted in the skeptics favor.

In 2013, the Institute of Medicine published a major review of the evidence connecting salt consumption and health outcomes. There was insufficient proof, the panel concluded, that heeding the U.S. recommended limit on sodium consumption improved health outcomes.

Then, this past August, the New England Journal of Medicine published the results of a massive research effort known as the PURE study. It indicated that people who conform to the U.S. recommended limits actually have more heart trouble.

To explain their findings, these researchers pointed to studies suggesting that low sodium may stimulate the production of renin, a hormone that may have harmful effects on blood vessels.

While food studies are often financed by the industry, the PURE study in the New England Journal of Medicine and the Institute of Medicine study were funded by governmental and other sources.

Since their inception more than 30 years ago, the salt guidelines have drawn criticism.

Some of the earliest notions that Americans were eating too much salt arose from international comparisons.

It turned out that in some cultures, especially isolated ones, people consumed less salt and had lower blood pressure.

In one influential 1973 paper, Lillian Gleiberman, a University of Michigan anthropologist, collected statistics for 27 different populations. It showed the lowest blood pressures were among the African Bushmen, the Chimbu of New Guinea, the Caraja of Brazil and the Eskimos. Each group consumed exceptionally low levels of salt.

Maybe, Gleiberman suggested, human bodies had not adapted to the higher salt available in modern societies.

“My major hypothesis was that people ate much less salt in prehistoric times,” Gleiberman, now retired, said by phone recently. “And that our bodies may not be prepared for the larger amounts of salt now available to us.”

But Gleiberman said her paper was intended to inspire more research, not to serve as the basis of dietary guidelines. Those remote peoples, she said, are too different from modern populations to make sound comparisons.

“They have a simpler life,” Gleiberman said. “They don’t have the obesity, the diabetes and the other problems we have. We can’t look at a no-salt culture and say, ‘If we just do that, we’d be OK.’

“I have friends who won’t eat anything with salt,” she said. “I tell them they’re foolish.”

Nevertheless, when a Senate committee led by Sen. George McGovern, D-S.D., in 1977 set out to issue national dietary goals, the international comparisons played a key role.

There was not much else to go on. Scientists told the committee there was general agreement that very high salt consumption could be harmful. But were Americans eating too much? That was a matter of dispute, scientists testified.

But when the committee published its “Dietary Goals,” it recommended reducing daily sodium consumption to a very, very low level — less than 1,200 milligrams per day.

It’s not clear where that figure came from, and it didn’t last long.

Three years later, the federal bureaucracy issued its dietary advice. It was the first version of the Dietary Guidelines. And while it advised people to lower their salt consumption, it did not specify an upper limit.

So the question lingered. The Dietary Guidelines said Americans were eating too much salt. But how much was too much?

In 1984, a major worldwide study known as Intersalt was launched, with scientists testing more than 10,000 people from 52 different populations.

Yet Intersalt, too, failed to settle the argument. When the results were published in 1988, many of the findings undercut the salt orthodoxy. For example, populations with saltier diets did not have significantly higher blood pressure. But another point favored the other side: In places where more salt was consumed, blood pressures rose more with age.

Both sides declared victory. Then, despite the muddle, Intersalt became the basis for strict U.S. salt guidelines, with the 1995 Dietary Guidelines recommended holding to just about today’s limit of 2,300 milligrams per day.

The strict salt limit had become a fixture of U.S dietary advice.

Many experts expect the 2015 Dietary Guidelines to hold to the existing 2,300 milligram limit.

Already, the 15-member advisory panel last month recommended keeping the limit, though it withdrew support for the even stricter 1,500 milligram limit for African-Americans and people over 50. It further called for measures to remove salt from American foods.

Cheryl Anderson, nutrition expert at the University of California at San Diego who led the advisory panel’s sodium working group, said the government should continue to offer salt guidelines despite some of the recent findings that have called them into question.

One of the major critical studies, the PURE investigation, included more than 100,000 people. Anderson said it was “respectable” and “an important contribution.”

But she said such studies may be misleading because researchers take only a limited number of urine samples. And, she said, that type of research, known as observational studies, may suffer from a problem known as “reverse causality.” That is, while the data suggested that low-salt diets may have caused cardiovascular problems, maybe it was just the reverse — that preexisting cardiovascular problems had led people to eat low-salt diets.

The authors of the PURE study took steps to minimize such bias, but in the end, Anderson said, the weight of the evidence favored the old salt warning.

“We can’t take any one study in isolation,” Anderson said. “We placed the new ones in the context of the body of literature on sodium — and we put the strongest recommendations forward.”

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