In 1684 the chemist Robert Boyle defined the “salty taste” in some body liquids such as blood, sweat or even tears. He established the salt concentration by evaporating the samples and verifying that there were salt crystals in the ashes.
Nearly a century after that, H.M. Rouelle, in 1776, isolated some urea crystals in the urine. The chemist J. Berzelius prooved that the salt concentrated in some parts of the body such as in the abdominal cavity or the surroundings of the lungs, the heart and the brain. The sodium is the sixth more plentiful element on earth. Due to its extreme reactivity it is very rare to be found pure (it reacts very violently to water). This abundance allows it to be a vital element in the development of some biological chemical reactions that support life. It is known the positive effect of saline in the solution of nutrients. The solution of salt in the liquids of a human being is called saltiness, while its maximum tolerance is called halotolerance.
The body keeps a homeostasis of salt concentration in some liquids through osmorregulation activities (thanks to the sodium channels in some cells). This is why, when the intake of salt is loss-making or the sodium concentration in liquids is less than 140 millimole per litre of blood plasma, the brain sends signs of emergency to the kidneys to reduce the excretion through urine. The operation of regulation in the concentration of salt in the liquids is done by the vasopressin, the antidiuretic hormone (ADH), as well as by the aldosterone (that controls sodium levels in blood). It is common that when the use of salt is stopped (or reduced), the body tends to eliminate liquids aiming to restablish the salt concentration in the body liquids and this effect can lead to an induced dehydratation. For this reason, people exposed to hot weather (like a journey through the desert) eat small amounts of salt to avoid extra sweating.
However, there are other sources of sodium that can replace salt in food, such as the chemical yeast, the monosodium glutamate, the sodium bicarbonate, etc. Sometimes some food can provide sodium to our diet, as milk does.
The necessary element in salt is sodium, very useful in blood pressure and extracellular liquids. The lack of salt is a very rare deficiency, because the presence of salt in food is almost omnipresent. It leads to other health issues affecting the bowel sodium absorption. The salt that an adult has can be transformed in around a quarter of kilo. Until mid-XX century, it was very tough to measure almost briefly the sodium concentration of the body liquids. The emergence of new instrumentation made possible a new test in a very short period of time (five minutes). One of the most known tests to guess the salt concentration in blood is the Fantus test.
The total abscence of salt in a diet is dangerous to health. A small quantity of salt is needed to keep some activities performed by the body, such as breathing and digesting. The lack of salt implies a lack of sodium called hyponatremia. The lack of sodium makes the patient to have signs and syntoms of apathy, weakness, fainting, anorexia, low blood pressure, circulatory collapse, shock and, eventually, death.
The doctor William Osler noticed in some cholera patients the physiological effects due to the lack of salt. Some authors have researched the lack of sodium in the human being, specially in soldiers during the Second World War.
In the year 1994, the COMA (Committee on Medical Aspects of Food and Nutrition Policy) recommended a reduction in the dairy intake of salt for the worldwide population up to 6 grams. In the report, it is mentioned the dangerous effects and impacts that imply an extra intake of salt because it favours some heart diseases. This recommendation is based on the evidence that currently the use of salt and the appearance of high blood pressure are related. In 2003, the SCAN (Scientific Advisory Committee on Nutrition), in the report about “salt and health”, reviews the COMA information and considers as acceptable the estimated numbers in 1994, from a nutritional point of view.