Sometimes, a study can show information that was not expected by the original developed plan. A clear example of such statement is a recent study published in the August 6, 2008 issue of Physiology & Behavior. Entitled, Salt Craving: The Psycho-biology of Pathogenic Sodium Intake. The purpose of the study was to look for reasons why people, who knew they needed to reduce their salt consumption, continued to consume more salt.
University of Iowa psychologist Kim Johnson and colleagues found in their research that when rats are deficient in sodium chloride, common table salt, they shy away from activities they normally enjoy, like drinking a sugary substance or pressing a bar that stimulates a pleasant sensation in their brains.
What is Salt?
Before discussing the study and its implications, what is salt? We all know salt shakers are found on almost every table, and salt is added to most recipes. Many of us remember from our science class that salt is a simple molecule formed by the combination of a sodium ion with a chloride ion. Na is the symbol for sodium and Cl is the symbol for chlorine. The symbol for sodium chloride is NaCl.
All of us need sodium in order for our bodies to function properly. Sodium and other electrolytes are essential to allow our bodies to maintain their proper level of hydration and for our cells to function properly. Sodium chloride is an essential element--the human body cannot long function without it.
Apparently, salt also is important for the proper operation of the digestive processes.
History of Salt
No one knows when man first began to obtain his sodium from salt and not from his diet. It is known that as early as 2500 B.C., salt had become considered essential to any civilization. Some historians speculate that the reason that civilizations first developed on the edges of deserts was because they were close to natural deposits of salt.
Roman soldiers were paid in salt; the word salary is derived from the Latin for salt. While salt is now very plentiful, until fairly recently it was difficult to find and transport. Some historians say that the first wars were not fought over water or property but over salt deposits.
Even when mechanical refrigeration lessened the need for salt in the 19th century, consumption continued in excess because people liked the taste and it had become fairly inexpensive. Today, 77 percent of our salt intake comes from processed and restaurant foods, like frozen dinners and fast food.
The authors acknowledge that the body needs salt, but they want to examine the premise that salt is becoming an abused, addictive substance -- almost like a drug. The authors point out that for most of our existence, the diets of most humans did not contain enough sodium. They state that a pleasure mechanism in the brain is activated when salt is consumed. Since humans sought to gain more pleasure and less pain, people ate salt and this supplied the sodium that our bodies needed.
According to the authors, the fact that in our modern society diets are high in salt has led many of us to consume more sodium than our bodies can safely handle. "Most of our biological systems require sodium to function properly, but as a species that didn't have ready access to it, our kidneys evolved to become salt misers," the study stated.
Too high sodium levels, like smoking, have been linked to increased cardiovascular disease and numerous other health problems. Since too high a sodium intake, like smoking, is something that can be controlled by a person, the authors wanted to find if there were reasons why people, knowing that they needed to lower their sodium intake, continued to consume too much sodium.
The authors said that lab rats would generally perform feats in order to get rewards. They gave the example of pressing a bar that rewarded them by getting a sugary substance to drink. However, if these same lab rats were deficient in sodium chloride, common table salt, they were much less active and even tended to avoid things like pressing the bar even though they knew that pressing the bar would get them a sugary reward.
"Things that normally would be pleasurable for rats didn't elicit the same degree of relish, which leads us to believe that a salt deficit and the craving associated with it can induce one of the key symptoms associated with depression," said Dr. Kim Johnson, one of the authors of the study.
One sign of addiction is using a substance even when it's known to be harmful. Many people are told to reduce sodium due to health concerns, but they have trouble doing so because they like the taste and find low-sodium foods bland.
Another strong aspect of addiction is the development of intense cravings when drugs are withheld. Experiments by Johnson and his colleagues indicated similar changes in brain activity whether lab rats are exposed to drugs or salt deficiency.
"This suggests that salt need and cravings may be linked to the same brain pathways as those related to drug addiction and abuse," Johnson said.
Daily Sodium Requirement
The authors of the University of Iowa study admit that the minimum sodium requirement for human health is debatable, but it is clear that in developed countries the average daily intake of sodium “far exceeds what is needed for survival”. They report that the worldwide average salt intake is about 10 g daily, whereas the US Food and Drug Administration’s recommended intake is only 4 g a day.
The researchers then discuss the history of salt consumption in humans, and cultural differences in salt consumption. They say that New Guinea Highlanders have low daily salt intake (about 0.5 g per day), and they have less cardiovascular disease than groups who consume the worldwide average per day. When salt is introduced as a food additive to people from this group, they initially find it unpleasant, but some authors have claimed that after repeated exposures they develop an “addiction”, similar to caffeine or nicotine addiction. Similar results are reported for chimpanzees.
Mood and Pleasure-Related Effects of Sodium Deficiency
The authors report that changes in mood are one of the first signs of an inadequate diet, and they discuss findings regarding various vitamins. They suggest that the effects of chemicals such as sodium, potassium, calcium, magnesium and phosphate on mood have largely not been studied. The authors say that people who lose large quantities of sodium through sweating while they work in extremely hot environments often experience fatigue, headache, difficulties concentrating and sleeping. These symptoms are often associated with depression.
They discuss a study from 1936 looking at the effects of sodium deficiency created by eating a no-sodium diet and inducing sweating for seven days. After being subjected to this, participants reported a loss of appetite, an inability to feel pleasure, difficulty concentrating, and a feeling of exhaustion. The authors also report a study in 21 people with chronic fatigue syndrome (CFS) and also with low blood pressure when they stood up suddenly (a condition known as postural hypo-tension).
These people were given a drug with sodium-retaining properties, and encouraged not to limit their sodium intake (about two-thirds of the people had been intentionally limiting their salt intake). This treatment improved CFS symptoms and low blood pressure in 16 of the participants, as well as improving scores on well-being and mood. They say that the increase in sodium intake and retention “may have contributed to the mood improvements” but that this was only speculative.
The authors also report on experiments in rats, including some studies from their laboratory. They say that their studies showed that treating rats with a specific drug that normally makes them ingest more sodium and removing their access to salt solutions reduced their sensitivity to activities that were usually rewarding, such as drinking a sugar solution, while the drug alone had little effect on these behaviors.
Rats that had been given another drug that made them urinate more (therefore depleting sodium) but had no salt solution to replenish their sodium levels, experienced a similar effect. This effect could be reversed by providing a salt solution. Depriving rats of sodium also showed lower heart rate variability, which is another sign often observed in people with depression.
They discuss the possibility that changes in levels of hormones connected with maintaining sodium levels in the body may be related to mood. For example, people with depression have been shown to have increased levels of a hormone that causes the body to retain sodium, and people with a disease that leads to high levels of this hormone sometimes show symptoms of depression. They also discuss studies which found that one particular drug for treating high blood pressure may also have mood-enhancing properties, but that other high blood pressure drugs were not found to have this effect.
University of Haifa Research
Well, looking at the same fact from a different angle brings an idea that adding more salt to your food may help to fight depression.
Researchers at the University of Haifa’s Department of Psychology confirmed that people crave salt partly because its main component, sodium, helps fight depression. “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 bio-psychologist at the University of Haifa’s Department of Psychology, who authored the study along with bio-statistician 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 1.500 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.
Sources and Additional Information: