Not long ago, the widespread marketing campaigns pronounced salt as being so bad for human health that it was called “white poison”. Multiple variations of the salt-free diets appear, so you can openly choose which food you prefer without salt.
However, when next time you reach for the salt shaker to flavor your chips, perhaps you need not feel so guilty about treating yourself. For researchers say salt acts as a natural anti-depressant, which may explain why we crave it despite the health risks associated with eating too much of it. While too much can lead to high blood pressure and heart disease, not enough could trigger “psychological depressions”, one of the recent studies says.
University of Iowa Study
The study, by researchers at the University of Iowa in the U.S., discovered that rats began to behave erratically and shun foods and activities they normally enjoyed when they were deprived of salt.
Psychologist Professor Alan Kim Johnson, who led the team, commented: “Things that normally would be pleasurable for rats didn't elicit the same degree of relish. This leads us to believe that a salt deficit and the craving associated with it can induce one of the key symptoms associated with depression.”
The study was funded by the National Heart, Lung and Blood Institute, National Institute of Diabetes and Digestive and Kidney Diseases, and the American Heart Association and published in the peer-reviewed journal Physiology and Behavior.
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.
It is believed the human body has, over centuries, developed a feel-good factor associated with salt, partly because it used to be so scarce. Roman legionnaires were paid in salt because of its value at the time - with the Latin name “salarium” leading to the word 'salary', used today to describe wages.
It was also used to preserve food by the Romans and until the invention of mechanical refrigeration in the 19th century. By then people had become so used to the taste that it came to be sold as a condiment on dinner tables.
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.
Here are some facts about salt that you may find interesting:
- The major factor for the location of London was because it was where salt haulers often had to stay for days at a time because of the high tides of the Thames.
- One of the first taxes on goods was levied on salt in 2200 BC in China.
- The most familiar reference to salt in the Bible was the story of Lot’s wife who was turned into a pillar of salt when she disobeyed the angels and looked back at the wicked city of Sodom.
- By 2000 BC, people knew that adding salt to food helped preserve it and, in the times before refrigeration, this was vital.
- The buying and selling of salt became one of the most important trading activities in the world.
- The origin of the phrase “He is not worth his salt” is thought to have originated when slaves were traded for salt.
- When an early Roman was in love he was said to be “salted.” A juicy piece of gossip is 'salacious' because an ancient Roman in love was said to be 'salted'.
- In many religions, salt was given as a blessing. It was thought to drive out evil spirits and was linked to fertility and sexual desire.
- The story of Judas Iscariot overturning a bowl of salt is thought to be the source of the common superstition that spilt salt is bad luck.
- Many researchers believe that tens of thousands of Napoleon's troops died during their retreat from Moscow because of salt depletion.
- Some U.S. Civil War historians believe that a major factor in the defeat of the South was that the South had no supply of salt. Not only did this lack of salt contribute to the salt depletion of its soldiers, but salt was needed to tan leather, dye cloth for uniforms and to preserve meat.
- Geologists estimate that there are enough salt deposits in the state of Kansas to supply the entire world's salt needs for several hundred thousand years.
- Today, high amounts of salt are found in almost all processed foods, and it is estimated that 77% of our salt intake comes from the foods we eat---not by adding salt to our food.
- The National Academy of Sciences recommends that Americans consume a minimum of 500 mg/day of sodium to maintain good health, but many of us consume much more.
- Although affected by our individual DNA and metabolism, the kidneys of most of us are able to eliminate the excess and unneeded sodium.
- For some, the inability of our kidneys to eliminate excess sodium can lead to serious health problems.
Studies in mammals have shown that a lack of sodium in the body triggers physiological changes to retain the body’s sodium levels, as well as behavioral changes that lead to a higher sodium consumption. Under such conditions, laboratory animals will even drink very salty solutions that they previously avoided, suggesting that the nervous system alters the perceived taste of these substances.
The authors say that people eating modern Western diets and laboratory animals eating standard animal food are likely to consume more sodium than they need. They also say that some mammals lacking in sodium will consume much more sodium than is needed to achieve normal levels. They suggest that such behavior in mammals is “out of step” with their actual need for sodium, and could be detrimental as excess sodium intake over an extended period can lead to adverse health effects, such as high blood pressure and heart failure.
The authors discuss studies in humans and animals which have suggested that persistent unsatisfied salt cravings can induce behaviors similar to those seen in depression. The cravings also cause changes in the regions of the brain that are involved in motivation, reward, drug sensitization and withdrawal. They say that this raises questions about these affects on behavior.
Such questions include whether animals that have been deprived of sodium consume excess amounts in case of future deprivation; whether sodium deprivation alters the sense of “reward” the animal’s brain feels when consuming it; and whether mood is affected by a reduction of sodium intake in animals expecting high-sodium diets. The authors subsequently discuss experiments in animals that look at brain changes associated with sodium deprivation, and studies in humans and animals that suggest that sodium deficiency can reduce the effect of usually pleasant and rewarding stimuli, and negatively affect mood.
Daily Sodium Requirement
The authors say 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 10g daily, whereas the US Food and Drug Administration’s recommended intake is only 4g 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 0.5g 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.
Pathophysiology of Excess Salt Intake
The researchers describe human studies looking at the effect of salt intake on blood pressure. These studies found that groups with low salt intakes had lower blood pressure than groups with higher salt intakes, and that reducing salt intake can reduce blood pressure in people with high blood pressure. Studies in animals showed similar results. The authors report that it is difficult to voluntarily reduce our salt intake because of the high levels of salt in processed foods; they say that 77% of our salt intake comes from processed and restaurant foods.
The authors discuss studies that look at the nervous system and hormonal mechanisms by which the body regulates appetite for sodium.
They also discussed the relationship between taste and sodium appetite. They say that salt receptors on the tongue pass messages to areas of the brain that play a role in mood, reward, motivation and addiction. The authors report that salt becomes more palatable when sodium is lacking, and that in cases of severe sodium deficiency, this helps the body to identify and consume sources of sodium.
There have been reports that people who have cravings for salty foods lose large amounts of sodium in their urine because of hormonal problems or because they take diuretic drugs. They also say that people with high blood pressure who have been on a low sodium diet for a long time find salty tastes more pleasant, and this may affect how well they stick to their prescribed diets. Similar increases in the acceptability of salty solutions in sodium-deficient rats are reported, as well as changes in nerve cells involved in taste perception and reward. They also discuss sensitization to sodium, and the changes in the hormonal and nervous system that may be related to this.
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 hypotension).
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 wellbeing 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.
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