That lovin' spoonful
Salt is poison
Salty history
Intersalt assault
Big study. Big problems?
Millimeters of megadeath
Finding common ground

Why add salt to the wound?
The concern over sodium dates back to World War II when Walter Kempner of Duke University treated severe hypertension with a low-salt diet of rice and fruit. While many scientists credited the reduction in sodium for the success, the high-potassium, low-fat diet probably also played a role.

Processed foods are a major source of sodium. This item contains close to half the recommended daily sodium intake.

In the 1960s, Lewis Dahl of Brookhaven National Laboratory studied a rat that got hypertension with a high-salt diet. Dahl persuaded many scientists that high sodium caused hypertension, but critics later noted that, if scaled to human size, the rats would have been eating the equivalent of 500 grams of salt a day.

That's beyond the famous potato-chip diet – we're thinking pure road salt! And the rats were missing some of their kidney mass, so they were abnormally slow to get rid of extra sodium.

But for a public eager for dietary advice, and a medical profession becoming more and more eager to dispense it, the sodium results were compelling enough. In 1979, the U.S. Surgeon General's report was the first blanket recommendation to reduce dietary salt.

How convincing was the evidence at that point? Pretty flimsy, charges David McCarron, a persistent critic of the salt hypothesis from Oregon Health Sciences University. In 1979, he writes, the only "information that was supported by valid scientific data regarding the role of salt in blood pressure control was:

Excessive sodium intake produced blood pressure increases under extreme conditions.

In patients with renal [kidney] disease, blood pressure decreased with severe sodium restriction.

Animal studies suggested a possible genetic link.

McCarron says that because this data supported the expected relationship between sodium and hypertension, the recommendation was made despite the lack of answers to "a vast number of issues that bear far more heavily on the relevance and rationality of national dietary recommendations," including:

Careful studies of the relationship between salt intake and blood pressure.

Randomized controlled studies of sodium reduction in people.

Ongoing studies of whether salt intake was related to cardiovascular diseases and deaths.

Information about the interactions of multiple nutrients.

In other words, the argument was inconclusive. What did the largest salt study find?