Science Isn't Black and White

Science isn't salt and pepper- it's not black and white, says Editor David Feder, in questioning the "science" behind the Center for Science in the Public Interest's recent attack on salt in processed foods.

By David Feder, RD, Editor

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Last week the Center for Science in the Public Interest (CSPI) declared salt in our diets a "forgotten killer" ("Salt: The Forgotten Killer," by Michael Jacobson, Ph.D., CSPI, 24 February 2005), responsible for 150,000 deaths annually. This is a strong statement, and I’m not against strong statements. But it's also an unequivocal statement and, as someone with a background in science, that disturbs me greatly. Science isn’t salt and pepper — it’s not black and white.

I taught nutrition and food science labs while I was a doctoral candidate for nutrition biochemistry and I pulled some time in labs conducting nutrition studies. In the course of my studies and in my career as a journalist I’ve read thousands of nutrition studies on a variety of topics. This includes the abovementioned 40-page report by CSPI, which purports to back up their unequivocal claim that salt bears the responsibility for killing otherwise healthy people.

In hop-scotching through the 93 references accompanying the study, I found a number of studies relating to subjects who had or were already at risk for hypertension; data for increased consumption in populations bearing only presumed connections to risk for increased blood pressure; outdated studies going back decades; governmental declarations against salt based on compendia of data not necessarily related; and assumptions based on differences in semantics rather than health outcome.

By differences in semantics I refer to one very significant aspect of the relationship between salt intake to blood pressure: The word "significant." In daily parlance, significant means "a whole lot." But in scientific terms, something is significant if it can be measured with reasonable statistical determination that the factor measured is the cause of the change. The amount itself could, in fact, be minuscule.

And this is where salt and blood pressure increase come in. Yes, a high salt diet has been shown to raise blood pressure. But by how much (and for how long)? Most studies, including those cited by CSPI, show increases of only a few points.

For example, in the oft-cited Dietary Approaches to Stop Hypertension (DASH) study, one of the biggest changes decreasing sodium intake in healthy adults achieved was 7.0 mm Hg systolic /3.8 mm Hg diastolic. This means someone with a blood pressure of 117/74 would see it change to 110/70. (High blood pressure is 140/90 and above. prehypertension is 125/80 and above.) Many of the changes observed in the DASH study were only a few mm or less. A change of 3 mm is so small it would not be detectable in an individual patient using the techniques used in most doctor's offices.

So the decrease may be statistically significant, but it’s not necessarily clinically significant within our current knowledge base.

It should be noted that blood pressure readings can vary that much based on a number of variables, including whether your blood pressure is taken while sitting or lying down, early in the day or late, on a full stomach or an empty stomach, or how stressful your day has been. What’s curious is that the conclusions of the DASH study were still to unequivocally recommend decreased salt consumption based on such results.

The CSPI report is worrisome overall because it is constructed in such a manner as to use its predetermined conclusion as basis for its hypothesis. CSPI is also guilty of deliberate blindness to a wealth of data indicating healthy people may enjoy salting their soup without fear of being struck down in the prime of their life by a demonic killer lurking in the dietary shadows. Such hysteria is unbecoming of a group claiming to base their pronouncements on science. The CSPI report "Salt: The Hidden Killer" is not so much science as it is alarmist sophistry.

Look for a more comprehensive article on salt and health in an upcoming issue of Wellness Foods magazine. Until then, I encourage you to read the CSPI report, the Salt Institute’s news release (reprinted below) and the Salt Institute’s archive of studies at www.saltinstitute.org.

To view the CSPI report, go to www.cspinet.org/new/pdf/killer_salt_final.pdf.

Salt: Right Question, Wrong Answer

Richard L. Hanneman, president of the Salt Institute, issued the following response statement to release February 24 of a report on salt by the Center for Science in the Public Interest:

“Mr. Jacobson’s conclusions represent his viewpoint, not science. His report fails the sniff test: it hasn’t been peer reviewed or published.

“That said, however, CSPI’s focus on whether the amount of salt we eat matters to our health is the right question. CSPI, however, has the wrong answer to the question. It’s right to ask whether cutting back salt will save lives. The government has been ducking that question for years, refusing to conduct a randomized clinical trial to provide evidence on this point. We know salt affects blood pressure: for some people cutting back salt lowers blood pressure; for others, it raises blood pressure. We also know reducing salt also adversely affects hormone systems, our nervous systems and our sensitivity to insulin.  It is the total effect of these impacts that determines the number of heart attacks. You can’t just assume that projected blood pressure falls will net a health benefit. We need the data from a clinical trial.

“In fact, the only evidence we have is from observational studies. There are no clinical trials at all. And, worldwide, there have been only a dozen observational studies reported. Eleven of the twelve show just the opposite of what Mr. Jacobson is saying. None of these eleven studies shows improved rates of heart attacks or strokes on low salt diets; three, in fact, show just the opposite – low-salt diets have higher risks of heart attacks. The twelfth study just came out and was done in Japan where the 'low salt' group actually consumed more salt than the average American. I haven’t had a chance to study it in detail yet, but its stated conclusions support Mr. Jacobson’s claim. But what about the other eleven studies? Many of the other eleven studies are quite large studies and none of them could find a population benefit in reducing dietary sodium.


“Mr. Jacobson says that diets too high in salt are responsible for 150,000 premature deaths each year in the United States. There is no evidence supporting this claim. In fact, the American Heart Association says 150,000 is exactly the total number of all Americans under age 65 who die of cardiovascular disease every year. Is Mr. Jacobson alleging all of them died from salt? Or is he saying the American Heart Association is wrong?

“This allegation is sophistry, pure and simple. It is based on a hidden assumption to tie together two well-known facts. First, we’ve known for 4,000 years that salt is an important factor in blood pressure, and, persuasive evidence shows that a two-thirds reduction in dietary salt will reduce average blood pressures by a few millimeters of pressure. And, second, we’ve known for much of the last century that populations with lower average blood pressure, even a few millimeters, have lower incidence of heart attacks and strokes. But that doesn’t mean that reducing dietary salt would lower the incidence of heart attacks. Perhaps it would. But perhaps other known cardiovascular factors such as the impacts of lowering dietary salt on the kidney hormone renin or on insulin sensitivity or on sympathetic nervous system response will cancel out the blood pressure effect. That is a question that deserves a clinical trial and that clinical trial has never been done.

“Let’s look at the evidence. It’s easy to make bombastic charges. Where’s the beef? We invite Mr. Jacobson to join with us in demanding the government conduct a randomized controlled trial of the cardiovascular outcomes of sodium reduction.”

Citations for the twelve studies are provided on the Salt Institute website at www.saltinstitute.org/healthrisk.html.  For further background, see www.saltinstitute.org/28.html.

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