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Michael F. Jacobson

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Confused About Salt?

Posted: 08/08/2012 1:59 pm

The world's leading health authorities -- from the American Heart Association to the World Health Organization -- have urged people to cut back on salt (sodium). And several experts have estimated that if Americans reduced their sodium consumption by half, that would save upward of 100,000 lives and billions of dollars in medical costs annually. There simply is no controversy: Medical experts are nearly unanimous that we're eating too much salt.

But in June, the New York Times' Sunday Review section -- one of the most prestigious pieces of real estate in journalism -- published, in my opinion, one of the most irresponsible articles I've ever seen. The article, by freelance writer Gary Taubes, argued that "the actual evidence to support [eating less salt] has always been so weak" and that eating less salt "can increase our likelihood of dying prematurely."

Times readers -- and the American public -- deserved better.

Out-of-context quotes. Mr. Taubes claimed that in 1972 the government started a program to prevent hypertension, encouraging the Americans to reduce sodium even though an eminent hypertension expert, Dr. Jeremiah Stamler of the Northwestern University Feinberg School of Medicine, had written that the evidence linking sodium to high blood pressure was "inconclusive and contradictory."

Unfortunately, Mr. Taubes yanked that quote out of context. In the very same paragraph, Dr. Stamler stated, "Despite the unclarities, the fact remains that a considerable body of evidence has been collected by clinical, animal-experimental, and epidemiologic research indicating a significant relationship among salt intake ... and blood pressure regulation." [1] He recommended that people with hypertension, as well as healthy people who had a family history of the disease, should cut their sodium intake to 2,000 milligrams a day (slightly above the 1,500 mg that is recommended for most adults today).

Ignored evidence. According to Mr. Taubes, "NIH has spent enormous sums of money to test the hypothesis" that too much salt is harmful, but all of the official governmental admonitions to cut the salt "all essentially rely on the results from a 30-day trial of salt."

In fact, the conventional advice is not based on one study, but on a mountain of research conducted over the past half-century. As I and seven of the world's leading hypertension experts, including Dr. Stamler, recently wrote to the New York Times,

The consistency, variety, and solidity of findings from multiple studies of varied types, not just one 30-day study, has led practically every nutrition and public health agency in the world to advise the general population to reduce sodium. The Centers for Disease Control and Prevention, National Institutes of Health, American Medical Association, American Heart Association, American Public Health Association, World Health Organization, and many other groups have advocated reducing sodium in both processed foods and in diets. Even the Grocery Manufacturers of America has encouraged its member companies to lower sodium levels in their products. In contrast to Mr. Taubes, policy makers got it right -- excess salt intake has a prominent role in the pathogenesis of elevated blood pressure, the leading cause of preventable mortality worldwide.

In other words, Mr. Taubes was dead wrong.

Faulty studies. Mr. Taubes relied on two meta analyses, which combine results from several studies, to argue that cutting salt has no benefit. But one meta analysis used studies that lasted less than a month. When researchers excluded the short studies, the benefits were clear.

The second meta analysis had two flaws. First, it included an Italian study in which patients with heart failure were severely salt-depleted due to high doses of diuretics. Those patients never should have been put on low-sodium diets. Second, the meta analysis separated people with normal vs. high blood pressure. That left too few people in each group to detect an effect of lower-sodium diets. When Feng J. He and Graham A. MacGregor, two of the world's leading salt researchers, combined the two groups, they found a 20 percent reduction in heart attacks and other cardiovascular "events."

Possible harm. What about Mr. Taubes' bombshell -- that a "slew" of studies proves that cutting back on salt is risky? Only one of the studies Mr. Taubes cited was a trial that randomly assigned people to either cut salt or not. (It was the above-mentioned trial of people with heart failure.)

The other three simply stated that people who reported consuming less salt (for whatever reason) had a higher risk of heart disease. Mr. Taubes implied that people ate less salt because they were health conscious, but that probably is an incorrect assumption. For instance, in one study, the low-sodium group included people who supposedly consumed only about 600 mg of sodium a day. Such a low sodium intake is a red flag, indicating either that those people were ill or that their 24-hour urine collections to assess sodium intake were incomplete. It is well-recognized among experts that underestimating sodium intake is a common and serious problem that can lead to spurious results.

Defenders of salt generally accept that people with high blood pressure should follow their doctors' advice to cut the salt. But they argue that even if research proved that salt raises blood pressure and that high blood pressure caused heart disease, no one study had shown that lowering salt directly prevents heart disease. Now that important study has been done, but Mr. Taubes failed to acknowledge its findings. The Trials of Hypertension Prevention documented a 30 percent reduction in cardiovascular disease among people who were counseled to reduce their salt intake. (One of the meta-analyses included the trial, but erroneously indicated that it reported no benefit.)

The Times article -- with its prominence, reference to scientific evidence, and contrarian perspective -- undoubtedly confused many people who were following experts' advice to look for lower-sodium foods and restaurant meals. But the timing of the article may have even more serious repercussions.

Years ago, the Institute of Medicine of the National Academy of Sciences concluded that the evidence was clear that Americans were consuming far too much sodium and recommended major reductions. Then, in a landmark 2010 report, the IOM concluded that food manufacturers had largely ignored health experts' admonitions since 1969 to voluntarily cut sodium levels: We're consuming more salt now than we did in 1969. Hence, the IOM recommended that the Food and Drug Administration set gradually tighter legal limits on sodium in processed foods. Mr. Taubes' article might give ammunition to those who want to prevent the FDA from doing just that. As we told the New York Times, "That would only mean more hypertension, heart disease, deaths, misery, and medical costs down the road."

CSPI nutrition director Bonnie Liebman contributed to this article.

Reference:

[1] Stamler, Jeremiah. Lectures on Preventive Cardiology. New York: Grune & Stratton, 1967. 261. Print.

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