Friday, January 8, 2016

The CDC needs to take a good look at the scientific evidence on salt

A publication called Healthline has a CDC report up which claims, “Americans are consuming too much salt.” The trouble, according to the CDC, is that Americans eat a lot of processed foods which are loaded with sodium.

A new report from the U.S. Centers for Disease Control and Prevention (CDC) states that roughly 90 percent of people in the United States — regardless of age, race, or gender — consume more than the 2,300 mg daily recommended amount of sodium. That’s only a teaspoon of table salt.

CDC Director Dr. Tom Frieden called it “alarming” that nine out of 10 adults and children consume too much salt. “The evidence is clear: too much sodium in our foods leads to high blood pressure, a major risk factor for heart disease and stroke,” Frieden said in a press release.

The evidence is clear? Really? Let’s see it. The CDC study assumes that evidence is there. However, its study only counts how much salt people are consuming. It never bothers to prove that salt consumption causes heart disease, strokes or even high blood pressure.

CDC director Tom Frieden may be alarmed, but he presents zero evidence whatsoever that “too much sodium in our foods” leads to any negative health consequences. The science is simply not there. If anything, there is a modest amount of evidence which suggests the opposite — a diet too low in sodium may cause health problems.

This week a meta-analysis of seven studies involving a total of 6,250 subjects in the American Journal of Hypertension found no strong evidence that cutting salt intake reduces the risk for heart attacks, strokes or death in people with normal or high blood pressure. 

In May European researchers publishing in the Journal of the American Medical Association reported that the less sodium that study subjects excreted in their urine—an excellent measure of prior consumption—the greater their risk was of dying from heart disease. These findings call into question the common wisdom that excess salt is bad for you, but the evidence linking salt to heart disease has always been tenuous.

More from Scientific American:

Intersalt, a large study published in 1988, compared sodium intake with blood pressure in subjects from 52 international research centers and found no relationship between sodium intake and the prevalence of hypertension. In fact, the population that ate the most salt, about 14 grams a day, had a lower median blood pressure than the population that ate the least, about 7.2 grams a day. 

In 2004 the Cochrane Collaboration, an international, independent, not-for-profit health care research organization funded in part by the U.S. Department of Health and Human Services, published a review of 11 salt-reduction trials. Over the long-term, low-salt diets, compared to normal diets, decreased systolic blood pressure (the top number in the blood pressure ratio) in healthy people by 1.1 millimeters of mercury (mmHg) and diastolic blood pressure (the bottom number) by 0.6 mmHg. That is like going from 120/80 to 119/79. 

The review concluded that "intensive interventions, unsuited to primary care or population prevention programs, provide only minimal reductions in blood pressure during long-term trials." A 2003 Cochrane review of 57 shorter-term trials similarly concluded that "there is little evidence for long-term benefit from reducing salt intake."

Despite a lack of evidence, the CDC has continued its campaign against salt. Here is more from the Healthline report:

The CDC says that 86 percent of people with hypertension still consume too much sodium even though they ingest less salt than people without the condition.

Although this finding by the CDC seems to contradict the notion that it is beneficial to reduce salt intake, it raises a related question: Is a person who does not have hypertension, but consumes more than the recommended amount of sodium in his diet, more likely to acquire high blood pressure down the road if he keeps eating “too much” salt? If the answer is no — and the evidence suggests it is — then why is the CDC recommending a low salt diet to people who don’t have high blood pressure?

Because sodium is so ubiquitous in the American diet, the CDC says a key strategy in lowering sodium intake is to reduce the sodium in the food supply, which some food companies have already begun doing. Many processed foods are now available in lower sodium versions.

This sounds a lot like the long-accepted, but purely bogus idea that it is better to eat a low-fat diet. There is no good evidence for that, either, and there never has been any.

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