Humans consume more sodium than any other animal, eating salt with almost every meal. But unlike the other basic tastes – sweetness, sourness and savoriness – the level of saltiness we seek out doesn’t come close to being explained by the mineral's known benefits.
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Now, researchers at the University of Haifa’s Department of Psychology say that people may crave salt partly because its main component, sodium, helps fight depression. The findings, published in the journal Appetite in April, could help us recognize the reasons for our craving and control our habit. Or not, but at least we'd know.
“You might think people eat salt because it tastes good. But the deeper question is: Why do we love the stuff?” said Professor Emeritus Micah Leshem, a biopsychologist at the University of Haifa’s Department of Psychology, who authored the study along with biostatistician professor Pavel Goldstein of the university’s Department of Statistics. “It turns out we aren’t just born loving salt. We also learn to love it because of its benefits.”
The average person, American or otherwise, consumes 1 1/2 teaspoons of salt, or 3,400 milligrams of sodium, a day – about 50 percent more than the United States recommends. To investigate what drives our salt consumption, Leshem and Goldstein analyzed the results of the 2007-2008 National Health and Nutrition Examination Survey, a series of studies of the health and nutrition of people in the U.S. They found that women with less salt in their diet are more likely to be depressed – and that depressed men and women are more likely to add salt to their food at the table.
While the findings do not prove cause and effect, they could help explain the well-established and mysterious fact that women suffer a higher rate of depression than men.
Shaking off depression
The researchers speculate that women may become depressed because of a lack of salt in their food and may try unsuccessfully to self-medicate by adding salt at the table. (Added salt only amounts to 3-to-5 percent of sodium consumption; the rest is found in the actual food, getting there either naturally or through processing.)
On the other hand, men eat more salt overall and so may unwittingly be doing a better job inoculating themselves against depression, Leshem and Pavel suggest
According to this theory, more sodium means less depression, and less sodium means more depression (within certain unknown limits). So just as Pavlov’s dog salivated in response to a bell it learned to associate with food, people like the taste of salt because they learn that sodium makes them happier – or at least less sad.
“If something does you good, you tend to begin to like that stuff,” said Leshem. “Salt might work as an antidepressant, which helps explain why we eat so much of it.”
Meanwhile, when sodium has long-term negative effects, like heart disease, the conditions develop too subtly to counter the positive association. (High blood pressure is often called a “silent killer” due to its lack of symptoms.)
How bad is salt for you, anyway? Researchers have recently called into question the science behind U.S. government guidelines, showing that in some cases, reducing salt consumption to recommended levels can actually be dangerous.
For what they're worth, though, U.S. dietary guidelines recommend keeping consumption of sodium below 2,300 milligrams a day, or 1,5000 milligrams for those at risk. Above those levels, the government says, blood pressure can increase, along with the risk of heart disease – like heart attack and stroke – the world’s leading cause of death.
A lifelong courtship
Leshem and Goldstein aren’t the first researchers to link salt and depression; they’re just the first to do it with human dietary information. Previous research has shown that the hormone system that regulates salt appetite also regulates depression and that activation of the system causes depression more often in women.
There is some evidence that high blood pressure inhibits the system. Sodium consumption has also been linked to depression in some animals.
Depression is far from the only determinant of salt consumption. In the study, the researchers also showed that growing children – from birth to 18 years old – eat more salt than adults.
This phenomenon, which was previously known, is often attributed to greater calorie consumption during growth. But Leshem and Goldstein found that salt consumption outstrips caloric consumption in children, suggesting that salt may be important for growth and may actually drive children’s outsized appetite, rather than vice versa. Children may then carry their affinity for salt into adulthood.
By contributing to a greater understanding of why we like salt, Leshem and Goldstein’s findings could help us control how much we actually eat. The first step, though, is to figure out how much salt we should be eating. In both cases, it is important to understand salt’s benefits, they say, not just its health risks.