FUNDAMENTALS OF FUNCTIONAL NUTRITION COURSE

THE ROLE OF AND

M o d u l e 6

FUNDAMENTALS OF FUNCTIONAL NUTRITION COURSE Lesson

2 Salt: historical perspective, science, and nutritional roles in the human body.

The significance of salt throughout history

Salt has played a major role in the development of our civilisation. It has been used as money, to flavour , in religious proceedings, to enhance the libido, and to ward off evil. Below we will explore a ‘snap-shot’ of the significant role that salt has played in the history of the world. The following reference 1 was used in this section as it provides an easy digestible account of this long history.

Stone Age: During this period people hunted and therefore obtained their salt from red meat.

Ten thousand BC: People began to farm the land, cultivating rice, wheat, barley, and millet, and reduced their red meat consumption. Thus, people required salt in their diets and to for the preservation of such as hams and . The cattle they kept on their farms also required salt.

Neolithic period: Settlements flourished around salt springs and caravans transported salt across the desert trading it for gold – ounce for ounce.

Six thousand BC: Northern China’s Lake YunCheng was documented as the first place people harvested and produced salt.

Ancient Egyptians 3000 BC: The Old Kingdom was preserving fish and meat with salt. They also used salt to preserve mummies. The Egyptians obtained salt by evaporating water from the Mediterranean Sea and buying it from nearby Libya, Sfax, Tunisia, and Nubia.

Chinese 800 BC: The Chinese produced salt by filling clay jars with sea water and boiling the water until only salt remained. Others who used evaporation to produce salt included the Etruscans of Italy, the early Romans, and the Carthaginians in North Africa.

Indo-European Celts 700 BC: The Celts were mining salt underground in what is now Austria, Hungary, South Germany, and Poland.

Ancient Greeks: sold their slaves in exchange for salt.

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2 As Napoleon was retreating from Moscow, many of his troops died because of the lack of salt.

Europeans in America: The first Europeans in America had great commercial success because they learned to salt the fish they caught in order to transport it to their home markets.

The Erie Canal in the United States was built primarily to transport salt.

The symbolic value of salt

The has both positive and negative connotations. According to an Arabic proverb; ‘salt is not worm-eaten’. Salt is white, immaculate, incorruptible, and imperishable” 2. durability and its immunity to decay made it an emblem of immortality. Salt also served as a recognition of loyalty, as illustrated by the ancient custom to share one’s bread and salt with the guest 2. As a reflection of its anti-bacterial properties, salt was also considered to have healing strength 2.

Salt was said to promote health. The Latin words for health and healthy, salus and saubris are actually derived from sal (salt) 2. Although salt was thought to be essential for health, the Chinese were sceptical. The famous Yellow Emperor wrote approximately 3000 BC ‘If too much salt is used in food, the pulse hardens, tears make their appearance and the complexion changes’2.

Salt was a precious commodity, often used as the equivalent of money. For example, in ancient Rome soldiers and officials were paid in the form of a ‘salarium’; salt money, from which the word salary comes from 1,2.

The symbol of salt also had some negative connotations. In biblical times, defeated and destroyed cities during war had salt spread over their territory 2. It was thought that salt belonged to the realm of evil, the deadly desert, and the land of sin. Even now, farmers in Bavaria still put salt into the brim of their hats to ward off evil 2.

The lack of salt

Salt hunger is well known in the animal kingdom. As early as 1884, Manley wrote: The ‘universal existence of an appetite for salt surely indicates that the substance serves more important functions that that of merely gratifying the palate’ 2. In fact, it has been suggested that one of the reasons why some species of wild

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2 animals could be domesticated into human settlements were because they were attracted by the salt content of human urine 2.

Salt deficiency occurs usually in remote regions a long way from the sea. It is not noted in carnivorous animals (which get a supply of salt from their prey’s blood and meat), but occurs in herbivores 2. Salt deficiency poses a serious risk in selection: speed and endurance are diminished when animals are trying to escape predators, thermoregulation is disturbed, and fertility is reduced 2.

In humans, lack of salt contributed to the development of the slave trade. In Africa, salt was traded for gold and it has been documented that natives even gave their wives and children away in exchange for salt 2.

Adding salt to food: how was this need met?

When did the need to add salt to food arise? Addition of salt to food by the hunters and gatherers was unknown, and is supported by more recent anthropological studies in New Guinea 2. The need to add salt arose when agriculture was introduced which led largely to a vegetarian diet.

How was the need for salt met?

Some populations satisfied their need for salt by cannibalism, others by drinking milk or animal blood and urine 2. Apart from these sources, salt was obtained by three main techniques.

1. obtained by the evaporation of sea water, 2. Mining of rock salt, and 3. Heating of the brine of (area for making salt).

Production of salt and its role in the beginnings of modern industry and capitalism

Salterns were the forerunners of industrial production and capitalistic organisations in Europe. At the end of the 16th century, salterns were faced with growing economic and ecological problems. For example, the use of wood to fuel the salterns became uneconomical because it had to be transported over great distances. Likewise, an ecological crisis arose because the forests were cleared to make way for new salterns. This was not surprising because 1 tonne of salt required 1.5 tonnes of wood2. Salt was also the driving force behind the

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2 construction of roads and canals around the world, and the expansion of cities (e.g. Venice) 3.

Salt today

Salt today is produced on an enormous scale. For example, in 2010, an estimated 270 million tonnes of salt was produced, a quantity far greater than the production of ammonia and sulphuric acid 3. So what do we do with all this salt? Well, we don’t eat most of it. It is estimated that only 2% of the salt produced each year goes to human or livestock consumption 3. In contrast, approximately 20% goes to roads in the winter months, and the vast remainder goes to the chemical industry 3.

☺ We all love a bit of salt, which may explain why it has been called the “primordial narcotic.” We tend to put it on everything even when it is not needed. For example, there are two camps of people when it comes to barbecues. The first say you should salt your meat before cooking – that way the salt can be absorbed into the meat and bring out the flavour. The second camp says that you should add salt after cooking; the argument goes that salting beforehand removes the juices from the meat by osmosis and it dries out. The second group is correct, but for the wrong reason. The structure of meat is such that osmosis does not occur, but the juices that are lost during cooking simply wash away any salt that was added to the surface of the meat. So you can salt before you cook if you wish, but it’s a waste 3.

Types of salt

Most of the world’s salt comes from seawater which contains dissolved minerals, rocks, and soil containing sodium and chloride, and from massive underground salt deposits 1. Salt deposits were formed millions of years ago when large bodies of water evaporated leaving behind rock salt () which formed the salt beds we find today 1.

Salt is used for various purposes, the most common being added to food for flavour. It is also added as a food preservative because bacteria do not grow well in salt-rich environments. The reason salt often has bad press as being unhealthy (in large amounts) is that it binds to water in the blood and raises blood pressure.

The great majority of salt in the western diet comes from processed foods.

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2 Table salt (refined salt)

The most common salt used today is plain table salt. This salt is highly refined and usually has anti-caking agents added to it to stop it clumping together. Refined salt undergoes processes that include bleaching, kiln drying, heating, and/or altering with chemicals 1. Iodine is often added to table salt as a successful public health campaign against iodine deficiency which is still common in many parts of the world. Iodine deficiency is the leading cause of hypothyroidism, mental retardation, and other health problems 4,5.

Kosher salt

Kosher salt is far less refined than table salt, and is thus a better example of a natural salt crystal 1. It is less likely to contain additives like anti-caking agents and iodine.

Sea salt

Like table salt, sea salt is mostly . However, it depends on where it is harvested and how it was processed and the kind of trace minerals it may contain (e.g. potassium, iron, and zinc). The darker the sea salt, the higher its trace mineral content and impurities. However, with ocean pollution becoming a major global problem, sea salt may contain some heavy metals like lead 6.

Himalayan pink salt

Himalayan pink salt is mined in the Khewra Salt Mines, Pakistan 1. It contains traces of iron oxide (rust) which gives it a pink colour. It also contains small amounts of calcium, iron, potassium, and magnesium and has a lower sodium content than regular salt 6.

The science of salt

The chemistry of salt is defined as the product formed from the neutralisation reaction of acids and bases.

Acids: acids are substances which produce hydrogen ions (H+) in solution (an ion is an atom or a molecule that has a charge). In the case of the hydrogen ion, the H has a positive charge. The hydroxide ion below has a negative charge.

Bases: bases are substances which produce hydroxide ions (OH-) in solution.

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2 Salts are ionic compounds composed of cations (positively charged ions) and anions (negatively charged ions). Because the salt is composed of cations and anions it is electrically neutral (that is, it has no charge).

Chemically, salt is 60.66% chloride (Cl-) and 39.34% sodium (Na+). Thus the reaction to form salt is as follows:

Na+ + Cl- = NaCl (sodium chloride: table salt)

Salt and the human body

Sodium is an essential mineral that is vital in the balance of body fluids. For example, the amount of bodily sodium is directly proportional to the volume of bodily fluid 7. Most people in the western world ingest more salt than is needed which can result in fluid volume expansion, edema, and elevated blood pressure. In contrast to sodium, ingestion of adequate amounts of potassium is associated with lower blood pressure and better cardiovascular performance 7.

Generalisations about sodium and salt

To understand the mechanism of sodium balance in the human body, it is necessary to differentiate between sodium and salt (sodium chloride). Sodium is an essential mineral that is vital in maintaining the balance of body fluids. The most common source of dietary sodium is table salt, sodium chloride.

The total sodium of a normal adult with a typical weight of 70 kg is approximately 4200 mmol (almost 100 grams) 7. Bone contains about 40 % of the total body sodium, and 60 % of sodium resides in the extracellular (50%) and intracellular fluid (10%) 7. Sodium stores are classified as exchangeable and non- exchangeable. Exchangeable sodium consists of all the intracellular and extracellular sodium and less than 50% of bone sodium. Non-exchangeable sodium is predominantly buried deep in bone tissue. Exchangeable sodium is highly important because when it is lost from the blood into the urine or faeces, it can rapidly be replaced from other compartments 7. The majority of chloride (approximately 70%) is distributed in the extracellular fluid. The remaining chloride can be found in collagen of connective tissue.

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2 Sodium balance: absorption, transport, and tissue distribution

The regulation of blood sodium occurs through a hormone system, which also regulates water balance, pH, and osmotic pressure 8. The hormones, angiotensin and aldosterone both facilitate sodium conservation by increasing sodium reabsorption by the kidney. When sodium is depleted, the enzyme renin is produced by the kidneys which generates active angiotensin into the blood circulation 8. Angiotensin stimulates constriction of blood vessels which increases blood pressure, decreases water loss, and stimulates the release of aldosterone from the adrenal cortex 8 (Figure 1). In contrast to sodium, chloride is distributed passively throughout the body and moves to replace anions by other mechanisms. The main excretory route for sodium and chloride is in urine. Sweat losses tend to be low unless extreme physical activity is performed. Faecal loss is also low in healthy individuals 8.

Figure 1: The renin-angiotensin system. 1. A decrease in blood pressure leads to the release of renin (2). Renin proceeds to activate angiotensin (3). Active angiotensin acts on the adrenal gland to produce aldosterone (5) and constricts blood vessels leading to an increase in blood pressure (4 and 5, in red). Aldosterone acts on the kidney to increase sodium and water retention (6 and 7) which leads to an increase in blood pressure. Figure produced using Servia Medical Art, www.servier.com

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2 Summary

Salt has played a major role in shaping our environment and civilisation. Salt has been used for many purposes throughout history, and has been particularly successful in stimulating our taste buds for more of this “primordial narcotic.” Salt comes in many types with each having a different composition of impurities or minerals. Although excess salt has been linked to elevated blood pressure and heart disease, its role in the human body is critical for maintaining the body’s fluid balance. This is achieved through the renin-angiotensin system.

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2 References 1 Moore, D. K. The Significance of Salt: an Introductory Lesson Module. Chemeketa Community College, Funded by a grant from the Department of Energy. 2 Ritz, E. The history of salt—aspects of interest to the nephrologist. Nephrology Dialysis Transplantation 11, 969-975 (1996). 3 Gibb, B. C. Salt of the Earth. Nature Chemistry 5, 547-548, doi:10.1038/nchem.1684 (2013). 4 The, L. Iodine deficiency?way to go yet. The Lancet 372, 88 (2008). 5 Pearce, E. N. Iodine deficiency in children. Endocrine development 26, 130-138, doi:10.1159/000363160 (2014). 6 Gunnars, C. http://authoritynutrition.com/different-types-of-salt/ 7 Preuss, H. G. & Clouatre, D. L. Sodium, chloride, and potasium. In Present knowledge in nutrition, 10th ed. Editors: John, W. Erdman Jr; Ian, A. Macdonald, and Steve, H. Zeisel. Wiley-Blackwell, Ltd. . 2012. 8 Strain, S. & Cashman, K. D. Minerals and trace elements. In, Introduction to Human Nutrition, 2nd Ed. Editors: Michael, J. Gibney; Susan, A. Lanham- New; Aedin Cassidy, and Hester, H. Vorster. John Wiley & Sons, Ltd. UK. . (2009).

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