For decades, the Centers for Disease Control and Prevention has been recommending that Americans cut back on their salt intake.
Officials claim that lowering how much sodium we eat would decrease the national burden of high blood pressure, heart disease, and even prevent deaths.
The official hard line is 2,300 milligrams (about one teaspoon) of sodium per day for a young, healthy person. For about half of the population, those over 40 or who already have high blood pressure, the recommended level is 1,500 milligrams.
This week is even World Salt Awareness week to raise awareness that we should be eating less salt.
The CDC's guidelines are mainly based on a theory and two studies. The first was performed in "salt-sensitive" rats that were fed 60 times the amount of salt in the average American's diet, and then developed high blood pressure.
The other is a short-term (30 days) study of people placed on a high salt diet: They were seen to have slightly higher blood pressure at the end of the trial, though they didn't look at long-term turnouts.
Even though the government has been pushing low salt diets for decades, salty foods have been making a comeback, even for so-called "healthy" chefs like Jamie Oliver, and researchers and doctors are starting to doubt the science behind the "recommended daily levels" of sodium intake.
They say the evidence just doesn't support the CDC's recommended level of salt intake.
A study published in the Journal of Hypertension in 2011 [PDF], which analyzed data from over 6,000 people, failed to find an association between lowered salt intake and lowered risk for heart attacks, strokes, or death.
Another 2011 study, published in the Journal of the American Medical Association, went even further, suggesting that a low-salt diet could actually be hurting us. They reported that the less sodium study subjects excreted in their urine, the greater their risk was of dying from heart disease.
Multiple studies over the years have shown similar findings, and even though we are eating more processed foods and doctors are pushing low-salt diets, a 2010 report in the American Journal of Clinical Nutrition indicated that Americans' salt intake hasn't changed in the last 50 years.
Yet Americans' rates of cardiac diseases has increased over the past 30 years, possibly because of our increasing rates of obesity, which could be playing a bigger role in these diseases than salt intake.
The study found that decade after decade, American adults ate 3,700 milligrams of sodium a day, similar to levels found in international studies. Some researchers think that this similarity is so stunning and consistent in different diets and cultures, that it could mean that humans have a set level of salt intake that we are hardwired to seek out, and that this level is higher than recommended doses.
"It's spooky how consistent this number is," David McCarron, a researcher at University of California, Davis, told USA Today in 2010.
The salt story just got more complicated, though. A study in Nature on March 6 indicated that a high salt intake is also linked to diseases in which the body's immune system attacks our own cells, like multiple sclerosis and type 1 diabetes.
Mouse cells produced more and more of a type of white blood cell linked to these auto-immune diseases when they were grown in higher and higher levels of salt. They also saw this in human cells in the lab and in a mouse model of multiple sclerosis — the mice progressed faster when fed a diet containing 4 percent sodium.
High salt diets would be just one of a number of factors that work together to cause these auto-immune diseases. And because the salt seems to be activating the immune system (albeit in a negative way in the case of multiple sclerosis), someone dying of cancer might actually improve their immune system with a high-salt diet, Hafler theorized.
Most of us should take this campaign with a grain of salt.
People with specific genetic traits that make them more susceptible to salt intake or those who already have really high blood pressure should still be careful about their salt levels. But the studies just don't support the idea that your average American needs to cut their salt intake drastically.
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