In the past, people thought that salt boosted health — so much so that the Latin word for “health” — “salus” — was derived from “sal” (salt). In medieval times, salt was prescribed to treat a multitude of conditions, including toothaches, stomachaches and “heaviness of mind.”
While governments have long pushed people to reduce their intakes of sodium chloride (table salt) to prevent high blood pressure, stroke and coronary heart disease, there are good reasons why cutting down on salt is not an easy thing to do.
“In biology, if something is attractive and we invest in gaining it, it must be beneficial, adaptive in evolutionary terms,” says Micah Leshem, a professor of psychology at Haifa University in Israel, who spent decades researching salt’s unique appeal.
People tend to consume about the same amount of sodium no matter where they live, and this amount hasn’t changed much in decades. Those facts hint at the biological basis of our sodium appetite.
A 2014 analysis of data that spanned 50 years and dozens of countries found that the quantity of sodium that most people consume falls into a historically narrow range of 2.6 to 4.8 grams per day. (And then there are extremes: In 16th-century Sweden, for example, people ate 100 grams a day, mostly from fish that had been salted to preserve it.)
Over the last five decades, salt content of commercial food in in the United States has gone up; but people’s 24-hour urinary sodium excretion have been constant. Irrespective of age, sex or race, between 1957 and 2003 Americans have been eating on average 3.5 grams of salt a day. Scientists therefore posit that we are somehow regulating the amount of salt we eat.
And, in fact, salt is good for us. Sodium is necessary for preventing dehydration, for proper transmission of nerve impulses and for normal functioning of cells. If we ate no sodium at all, we would die. When animals become sodium-deficient, they often go out of their way to find the mineral. That’s why, for example, sweaty clothes of alpinists tend to attract mountain goats.
Once sodium deficiency is experienced, salt cravings can last a lifetime. That happens with humans — but only if the deficiency strikes in very early childhood, or even before birth.
If your mother suffered frequent vomiting in pregnancy or if you lost significant amounts of
sodium as a baby (due to vomiting or diarrhea, for example), chances are good that you eat more salt than other people do, even by as much as 50 percent, as one of Leshem’s studies has shown. This is probably because sodium depletion alters our central nervous system so that we develop long-lasting preference for the mineral.
In one of Leshem’s studies, babies who had low concentrations of sodium in their blood in the first weeks of their lives grew up to be teenagers with a penchant for salt, even salt that is seemingly hidden in processed foods. “Even if you can’t taste the salt, apparently your body does. It’s working on an unconscious level to condition a preference for sodium,” Leshem explains.
Eating salt may also help calm us, or reduce our stress. In animal studies, the effects are pretty clear. An experiment published in 1995 showed, for example, that when rats are put in stressful situations, they choose to drink salty water rather than unsalted water. In another study, when wild rabbits were stressed, their sodium intake shot up.
The possibly stress-reducing, or mood-enhancing, effects of salt in humans are not as well documented, but there is some evidence. In a 2014 study involving about 10,000 Americans, Leshem and his colleagues found a relationship between salt intake and depression: Women whose diets were high in sodium were less depressed than other women. “Maybe people are self-medicating with salt,” he reasons. “But that’s a small effect; salt is not going to cure anyone of depression.”
It’s also possible that sodium aids growth. As scientists from New Jersey Medical School found out, if you put rats on low-salt diets, their bones and muscles fail to grow as fast as they normally would. In one of his experiments, Leshem found that children in general reach for more salt than adults do – independent of calorie intake – which may be explained by the needs of their growing bodies.
In 1940 the case of a little boy was described in the Journal of the American Medical Association. From the time he was a year old, the boy would go out of his way to eat massive amounts of salt. When he started speaking, one of his first words was “salt.” During a hospital stay (unrelated to his dietary habits), he was put on a low-sodium diet. To prevent him from sneaking around the hospital and stealing salt, he was strapped to his bed. He soon died. The reason? Due to severe and undiagnosed cortico-adrenal insufficiency, his kidneys were unable to retain sodium. Only eating huge amounts of salt had kept the boy alive.