Salt

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This article is about common table salt. For other uses, see Salt (disambiguation).
Salt
Brine being boiled down to produce salt at the Xinhai Well in Zigong, People's Republic of China
The salt works north of Pondicherry, India.

Salt, also known as table salt, or rock salt, is a crystalline mineral that is composed primarily of sodium chloride (NaCl), a chemical compound belonging to the larger class of ionic salts. It is essential for animal life in small quantities, but is harmful to animals and plants in excess. Salt is one of the oldest, most ubiquitous food seasonings and salting is an important method of food preservation. The taste of salt (saltiness) is one of the basic human tastes.

Salt for human consumption is produced in different forms: unrefined salt (such as sea salt), refined salt (table salt), and iodized salt. It is a crystalline solid, white, pale pink or light gray in color, normally obtained from sea water or rock deposits. Edible rock salts may be slightly grayish in color because of mineral content.

Chloride and sodium ions, the two major components of salt, are needed by all known living creatures in small quantities. Salt is involved in regulating the water content (fluid balance) of the body. The sodium ion itself is used for electrical signaling in the nervous system.[1] Because of its importance to survival, salt has often been considered a valuable commodity during human history. However, as salt consumption has increased during modern times, scientists have become aware of the health risks associated with too much salt intake, including high blood pressure. Therefore health authorities have recommended limitations of dietary sodium.[2][3][4][5][6] The United States Department of Health and Human Services recommends that individuals consume no more than 1500–2300 mg of sodium (3750–5750 mg of salt) per day depending on age.[7]

Evaporation pans in the 'Salt Valley' of Añana, Spain

Contents

History

Main article: History of salt
Salt production in Halle, Saxony-Anhalt (1670)
Sea salt harvesting in Pak Thale, Phetchaburi, Thailand

While people have used canning and artificial refrigeration to preserve food for the last hundred years or so, salt has been the best-known food preservative, especially for meat, for many thousands of years.[8] A very ancient saltworks operation has been discovered at the Poiana Slatinei archaeological site next to a salt spring in Lunca, Neamţ County, Romania. Evidence indicates that Neolithic people of the Precucuteni Culture were boiling the salt-laden spring water through the process of briquetage to extract the salt as far back as 6050 BC.[9] The salt extracted from this operation may have had a direct correlation to the rapid growth of this society's population soon after its initial production began.[10] The harvest of salt from the surface of Xiechi Lake near Yuncheng in Shanxi, China dates back to at least 6000 BC, making it one of the oldest verifiable saltworks.[11]:18–19

Salt was included among funereal offerings found in ancient Egyptian tombs from the third millennium BC, as were salted birds and salt fish.[11]:38 From about 2800 BC, the Egyptians began exporting salt fish to the Phoenicians in return for Lebanon cedar, glass, and the dye Tyrian purple; the Phoenicians traded Egyptian salt fish and salt from North Africa throughout their Mediterranean trade empire.[11]:44

Along the Sahara, the Tuareg maintain routes especially for the transport of salt by Azalai (salt caravans). In 1960, the caravans still transported some 15,000 tons of salt, but this trade has now declined to roughly a third of this figure.[12]

Salzburg, Hallstatt, and Hallein lie on the river Salzach in central Austria, within a radius of no more than 17 kilometres. Salzach literally means "salt water" and Salzburg "salt city", both taking their names from the German word for salt, Salz.

Hallstatt gave its name to the Celtic archaeological culture that began mining for salt in the area in around 800 BC. Around 400 BC, the Hallstatt Celts, who had heretofore mined for salt, began open pan salt making. During the first millennium BC, Celtic communities grew rich trading salt and salted meat to Ancient Greece and Ancient Rome in exchange for wine and other luxuries.[8]

The word salary originates from Latin: salarium which referred to the money paid to the Roman Army's soldiers for the purchase of salt.[13][14][15] The word salad literally means "salted," and comes from the ancient Roman practice of salting leaf vegetables.[11]:64

Mahatma Gandhi led at least 100,000 people on the "Dandi March" or "Salt Satyagraha", in which protesters made their own salt from the sea, which was illegal under British rule, as it avoided paying the "salt tax". This civil disobedience inspired millions of common people, and elevated the Indian independence movement from an elitist struggle to a national struggle.

Forms of salt

Unrefined salt

Main articles: Sea salt, Halite, and Fleur de sel
A commercial pack of sea salt

Different natural salts have different mineralities, giving each one a unique flavor. Fleur de sel, a natural sea salt from the surface of evaporating brine in salt pans, has a unique flavor varying from region to region. In traditional Korean cuisine, so-called "bamboo salt" is prepared by roasting salt[16] in a bamboo container plugged with mud at both ends. This product absorbs minerals from the bamboo and the mud, and has been shown to increase the anticlastogenic and antimutagenic properties of doenjang.[17]

Completely raw sea salt is bitter because of magnesium and calcium compounds, and thus is rarely eaten.[citation needed] The refined salt industry cites scientific studies saying that raw sea and rock salts do not contain enough iodine salts to prevent iodine deficiency diseases.[18]

Unrefined sea salts are also commonly used as ingredients in bathing additives and cosmetic products. One example is bath salts, which uses sea salt as its main ingredient and combined with other ingredients is used for its alleged healing and therapeutic effects.[citation needed]

Refined salt

Salt mounds in Salar de Uyuni, Bolivia

Refined salt, which is most widely used presently, is mainly sodium chloride. Food grade salt accounts for only a small part of salt production in industrialized countries (3% in Europe[19]) although worldwide, food uses account for 17.5% of salt production.[20] The majority is sold for industrial use. Salt has great commercial value because it is a necessary ingredient in many manufacturing processes. A few common examples include: the production of pulp and paper, setting dyes in textiles and fabrics, and the making of soaps and detergents.

The manufacture and use of salt is one of the oldest chemical industries.[21] Salt can be obtained by evaporation of sea water, usually in shallow basins warmed by sunlight;[22] salt so obtained was formerly called bay salt, and is now often called sea salt or solar salt. Rock salt deposits are formed by the evaporation of ancient salt lakes,[23] and may be mined conventionally or through the injection of water. Injected water dissolves the salt, and the brine solution can be pumped to the surface where the salt is collected.

Jagged salt pinnacles at the Devil's Golf Course in Death Valley National Park, US
Close-up view of salt crystals at Devil's Golf Course

After the raw salt is obtained, it is refined to purify it and improve its storage and handling characteristics. Purification usually involves recrystallization. In recrystallization, a brine solution is treated with chemicals that precipitate most impurities (largely magnesium and calcium salts).[24] Multiple stages of evaporation are then used to collect pure sodium chloride crystals, which are kiln-dried.

Table salt

In Western cuisines, salt is used in cooking, and also made available to diners in salt shakers on the table.

Table salt is refined salt, which contains about 97% to 99% sodium chloride.[25][26][27] It usually contains substances that make it free-flowing (anticaking agents) such as sodium silicoaluminate or magnesium carbonate. Some people also add a desiccant, such as a few grains of uncooked rice,[28] or a saltine cracker[29] in salt shakers to absorb extra moisture and help break up clumps when anticaking agents are not enough. Table salt has a particle density of 2.165 g/cm3, and a bulk density (dry, ASTM D 632 gradation) of about 1.154 g/cm3.[30]

Additives in table salt

Most table salt sold for consumption contains a variety of additives, which address a variety of health concerns, especially in the developing world. The amounts of additives vary widely from country to country.

Iodine and iodide
Main article: Iodized salt

Iodine-containing compounds are added to table salt. Iodized salt is thus table salt mixed with a minute amount of potassium iodide, sodium iodide, or sodium iodate. A small amount of dextrose may also be added to stabilize the iodine.[31]

Iodized salt is used to help reduce the incidence of iodine deficiency in humans. Iodine deficiency affects about two billion people and is the leading preventable cause of mental retardation.[32] The practice began in 1924.[33]Iodine deficiency commonly leads to thyroid gland problems, specifically endemic goiter, a disease characterized by a swelling of the thyroid gland, usually resulting in a bulbous protrusion on the neck. Iodized table salt has significantly reduced disorders of iodine deficiency in countries where it is used.[34] Iodine is important to prevent the insufficient production of thyroid hormones (hypothyroidism), which can cause goiter, cretinism in children, and myxedema in adults.

The amount of iodine and the specific iodine compound added to salt varies from country to country. In the United States, the Food and Drug Administration recommends [21 CFR 101.9 (c)(8)(iv)] 150 micrograms of iodine per day for both men and women. US iodized salt contains 46–77 ppm (parts per million), whereas in the UK the iodine content of iodized salt is recommended to be 10–22 ppm.[35] Today, iodized salt is more common in the United States, Australia and New Zealand than in the United Kingdom.

Fluoride

Especially in countries that have not benefited from fluoridated toothpastes and fluoridated water, fluoride salts are added to table salt. The practice is more common in some European countries, where water fluoridation is not practiced. In France, 35% of sold table salt contains sodium fluoride.[36]

Anti-caking agents

Sodium ferrocyanide, also known as yellow prussiate of soda, is sometimes added to salt as an anticaking agent. The additive is considered safe for human consumption.[37][38] Such anti-caking agents have been added since at least 1911 when magnesium carbonate was first added to salt to make it flow more freely.[39][40] The safety of sodium ferrocyanide as a food additive was found to be provisionally acceptable by the Committee on Toxicity in 1988.[37] Some other anticaking agents include tricalcium phosphate, calcium or magnesium carbonates, fatty acid salts (acid salts), magnesium oxide, silicon dioxide, calcium silicate, sodium aluminosilicate, and calcium aluminosilicate. Both the European Union and the United States Food and Drug Administration (FDA) permitted the use of aluminum in the latter two compounds.[41]

Iron

In "doubly fortified salt", both iodide and iron salts are added. This additive alleviates iron deficiency anemia, which interferes with the mental development of an estimated 40% of infants in the developing world. A typical iron source is ferrous fumarate.[36]

Other additives

Another additive, especially important for pregnant women, is folic acid (vitamin B9), which gives the table salt a yellow color. Folic acid helps prevent neural tube defects (NTDs) and anemia, which affect young mothers, especially in developing countries.[36]

In Canada, at least one brand (Windsor Salt) contains inverted sugar syrup.[citation needed]

Salty condiments

In many East Asian cultures, salt is not traditionally used as a condiment.[42] In its place, condiments such as soy sauce, fish sauce and oyster sauce tend to have a high sodium content and fill a similar role to table salt in western cultures. They are most often used for cooking rather than as table condiments.

Health effects

SEM image of a grain of table salt

Acute effects

Too much or too little salt in the diet can lead to muscle cramps, dizziness, or electrolyte disturbance, which can cause neurological problems, or death.[43] Drinking too much water, with insufficient salt intake, puts a person at risk of water intoxication (hyponatremia). Salt is sometimes used as a health aid, such as in treatment of dysautonomia.[44]

Death can occur by ingestion of large amounts of salt in a short time (about 1 g per kg of body weight).[45] Deaths have also resulted from attempted use of salt solutions as emetics, forced salt intake, and accidental confusion of salt with sugar in child food.[46]

Long-term effects

The effect of salt consumption on long term health outcomes is controversial.[47] The effects of salt reduction appears to have an unclear effect on mortality[48] and its effect on morbidity is contentious.[47][49]

Some associations include:

  • Stroke and cardiovascular disease.[50]
  • High blood pressure: Evidence shows an association between salt intakes and blood pressure among different populations and age range in adults.[51] Reduced salt intake also results in a small reduction in blood pressure.[47]
  • Left ventricular hypertrophy (cardiac enlargement): "Evidence suggests that high salt intake causes left ventricular hypertrophy, a strong risk factor for cardiovascular disease, independently of blood pressure effects."[51] "...there is accumulating evidence that high salt intake predicts left ventricular hypertrophy."[52] Excessive salt (sodium) intake, combined with an inadequate intake of water, can cause hypernatremia. It can exacerbate renal disease.[43]
  • Edema: A decrease in salt intake has been suggested to treat edema (fluid retention).[43][53]
  • Stomach cancer is associated with high levels of sodium, "but the evidence does not generally relate to foods typically consumed in the UK."[54] However, in Japan, salt consumption is higher.[55]

The Cochrane Collaboration found that "a modest and long term reduction in population salt intake [...] would result in a lower population blood pressure, and a reduction in strokes, heart attacks and heart failure. Furthermore, our study is consistent with the fact that the lower the salt intake, the lower the blood pressure."[56] Some isolated cultures, such as the Yanomami in South America, have been found to consume little salt and are still capable of regular activity. This may indicate an adaptation of humans to low levels of sodium that originated in the predominantly vegetarian diet of human primate ancestors.[57]

In 1994, the British Medical Journal published a randomized double blind placebo controlled study examining 100 Dutch middle-aged and elderly subjects with mild to moderate hypertension. A low sodium, high potassium, high magnesium mineral salt was used at the table and in foods given to the intervention group, with the control group ordinary table salt in their foods and at the table. Over a 24-week period, the researchers found a reduced blood pressure in the intervention group, with mean blood pressure falling by 7.6 mm Hg (systolic) and 3.3 mm Hg (diastolic) in the mineral salt group compared with the control group.[58] However, critics have pointed out that it is possible that some of the subjects may have changed their dietary habits due to many of them being able to distinguish the mineral salt from table salt due to their different taste.[59]

According to The Mayo Clinic and Australian Professor Bruce Neal, the health consequences of ingesting sea salt or regular table salt are the same, as the content of sea salt is still mainly sodium chloride. [60][61]

In traditional Korean cuisine, juk-yeom (죽염, 竹鹽), which means "bamboo salt", is prepared by roasting salt at temperatures between 800 and 2000 °C[16] in a bamboo container plugged with mud at both ends. This product absorbs minerals from the bamboo and the mud, and has been shown to increase the anticlastogenic and antimutagenic properties of the fermented soybean paste known in Korea as doenjang.[17]

A salt mill for sea salt.

Pathophysiology

Sodium is one of the primary electrolytes in the body.

Recommended intake

Recommended intakes of salt are usually expressed in terms of sodium intake. Salt (as sodium chloride) contains 39.3% of sodium by weight.

Country Description Sodium intake
mg per day		 Salt intake
mg per day		 Authority Remarks
United Kingdom The Reference Nutrient Intake (RNI) defined for a typical adult RNI: 1600 RNI: 4000 Scientific Advisory Committee on Nutrition (SACN) (2003)[62] However, average adult intake is two and a half times the RNI. SACN states, "The target salt intakes set for adults and children do not represent ideal or optimum consumption levels, but achievable population goals." The Food Safety Authority of Ireland endorses the UK targets.[52]
Canada An Adequate Intake (AI) and Upper Limit (UL) recommended for persons aged 9 years or more. AI: 1200–1500
UL: 2200–2300		 AI: 3000–3750
UL: 5500–5750		 Health Canada (2005)[63]
Australia and New Zealand An Adequate Intake (AI) and an Upper Level of intake (UL) defined for adults AI: 460–920
UL: 2300		 AI: 1150–2300
UL: 5750		 NHMRC (2006)[64] Not able to define a recommended dietary intake (RDI)
United States An Upper Limit (UL) defined for adults. A different upper limit defined for the special group comprising people over 51 years of age, African Americans and people with hypertension, diabetes, or chronic kidney disease (regardless of age). UL: 2300
UL for special group: 1500		 UL: 5750
UL for special group: 3750		 Department of Agriculture and Department of Health and Human Services (2010)[7][65][66] The Food and Drug Administration itself does not make a recommendation, but refers readers to the dietary guidelines given by this authority.[67]

A 2009 meta-analysis found that the sodium consumption of 19,151 individuals from 33 countries fit into the narrow range of 2,700 to 4,900 mg/day. The small range across many cultures, together with animal studies, suggest that sodium intake is tightly controlled by feedback loops in the body, making recommendations to reduce sodium consumption below 2,700 mg/day potentially futile.[68]

Labeling

UK: The Food Standards Agency defines the level of salt in foods as follows: "High is more than 1.5 g salt per 100 g (or 0.6 g sodium). Low is 0.3 g salt or less per 100 g (or 0.1 g sodium). If the amount of salt per 100 g is in between these figures, then that is a medium level of salt." In the UK, foods produced by some supermarkets and manufacturers have ‘traffic light’ colors on the front of the pack: Red (High), Amber (Medium), or Green (Low).[69]

USA: The FDA Food Labeling Guide stipulates whether a food can be labeled as "free." "low," or "reduced/less" in respect of sodium. When other health claims are made about a food (e.g., low in fat, calories, etc.), a disclosure statement is required if the food exceeds 480 mg of sodium per 'serving.'[70]

Campaigns

In 2004, Britain's Food Standards Agency started a public health campaign called "Salt – Watch it", which recommends no more than 6g of salt per day; it features a character called Sid the Slug and was criticised by the Salt Manufacturers Association (SMA).[71] The Advertising Standards Authority did not uphold the SMA complaint in its adjudication.[72] In March 2007, the FSA launched the third phase of their campaign with the slogan "Salt. Is your food full of it?" fronted by comedienne Jenny Eclair.[73]

The University of Tasmania's Menzies Research Institute maintains a website[74] to educate people about the problems of a salt-laden diet.

Consensus Action on Salt and Health (CASH)[75] established in 1996, actively campaigns to raise awareness of the harmful health effects of salt. The 2008 focus includes raising awareness of high levels of salt hidden in sweet foods and marketed towards children.[76]

In January 2010, New York City launched the National Salt Reduction Initiative, modeled after an initiative in the United Kingdom. The campaign calls on food makers to voluntarily reduce the amount of sodium in their foods, from 20% in peanut butter to a 40% reduction in canned vegetables, with an overall goal of reducing sodium in packaged and restaurant foods by 25% by 2015.[77]

A number of major food producers have pledged to reduce the sodium content of their food. Pepsi is developing a “designer salt” that’s slightly more powdery than the salt it regularly uses. The company hopes this new form of salt will cut sodium levels by 25% in its Lay’s potato chips.[78] Nestlé's prepared foods company, which produces frozen meals, announced that it will reduce sodium in its foods by 10% by 2015.[79] General Mills announced that it will reduce the sodium content of 40% of its foods by about 20% by 2015.[80]

Taxation of sodium has been proposed as a method of decreasing sodium intake and thereby improving health in countries like the United States where typical salt consumption is high.[81][82]

The Salt Institute, a salt industry body, is active in promoting the use of salt,[83] and questioning or opposing restrictions on salt intake.[84]

Lowering salt in diet

A low sodium diet reduces intake of sodium by selection of food and potentially by use of salt substitutes. Sea salt has the same sodium content as table salt.[60][85] [86][dead link]

Production

Main article: List of countries by salt production
Global salt output in 2005

Salt is produced by evaporation of seawater or brine from other sources, such as brine wells and salt lakes, and by mining rock salt, called halite.

In 2002, total world production (of sodium chloride in general, not just table salt) was estimated at 210 million tonnes, the top five producers being the United States (40.3 million tonnes), China (32.9), Germany (17.7), India (14.5), and Canada (12.3).[87]

Non-dietary uses and occurrences

Main article: Sodium chloride

Apart from its use in table salt in the diet, sodium chloride is a major industrial chemical. It occurs widely, being the main saline component of the oceans, and plays a role in formation of clouds.

Usage in religion

The Dead Sea is said to be the site of Sodom and Gomorrah. The salt concentration in it is so high that it allows the body to float easily with no effort at all

In the Hebrew Bible, thirty-five verses mention salt,[88] one of which being the story of Lot's wife, who, according to the legend, was turned into a pillar of salt when she looked back at the cities of Sodom and Gomorrah (Genesis 19:26) as they were destroyed. When King Abimelech destroyed the city of Shechem, he is said to have "sown salt on it," probably as a curse on anyone who would re-inhabit it. (Judges 9:45) The Book of Job contains the first mention of salt as a condiment. "Can that which is unsavory be eaten without salt? or is there any taste in the white of an egg?" (Job 6:6)

In the Christian New Testament, six verses mention salt. In the Sermon on the Mount, Jesus referred to his followers as the "salt of the earth". The apostle Paul also encouraged Christians to "let your conversation be always full of grace, seasoned with salt" (Colossians 4:6).

In one of the Hadith recorded in Sunan Ibn Majah, Prophet Muhammad is reported to have said that: "Salt is the master of your food. God sent down four blessings from the sky – fire, water, iron and salt"

Salt is mandatory in the rite of the Tridentine Mass.[89] Salt is used in the third item (which includes an Exorcism) of the Celtic Consecration (cf. Gallican Rite) that is employed in the consecration of a church. Salt may be added to the water "where it is customary" in the Roman Catholic rite of Holy water.

Salt is considered to be a very auspicious substance in Hinduism, and is used in particular religious ceremonies like housewarmings and weddings. In Jainism, devotees offer raw rice and a pinch of salt before a deity to signify their devotion.

In Judaism, it is recommended to have either a salty bread or to add salt to the bread if this bread is unsalted when doing Kiddush for Shabbat. It is customary to spread some salt over the bread or to dip the bread in a little salt when passing the bread around the table after the Kiddush.[90] To preserve the covenant between their people and God, Jews dip the Sabbath bread in salt.[91]

In Wicca, salt is symbolic of the element Earth. It is also believed to cleanse an area of harmful or negative energies. A dish of salt and a dish of water are almost always present on an altar. The salt is mixed with the water to consecrate it, in effect producing holy water. This mixture is used in a wide variety of rituals and ceremonies.

In the native Japanese religion Shinto, salt is used for ritual purification of locations and people (harae, specifically shubatsu), such as in sumo wrestling, and small piles of salt called morijio (盛り塩?, pile of salt) or shiobana (塩花?, salt flowers) are placed in dishes by the entrance of establishments for the two-fold purposes of warding off evil and attracting patrons.[92]

In Aztec mythology, Huixtocihuatl was a fertility goddess who presided over salt and salt water.

The ancient Egyptians, Greeks and Romans invoked their gods with offerings of salt and water. Some think this to be the origin of Holy Water in the Christian faith.[91]

See also

Ship loading salt at a terminal in the Port of Areia Branca, Brazil

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Bibliography

  • Barber, Elizabeth Wayland (1999). The Mummies of Ürümchi. New York: W.W. Norton & Co. ISBN 0-393-32019-7. OCLC 48426519. 
  • Kurlansky, Mark (2002). Salt: A World History. New York: Walker & Co. ISBN 0-8027-1373-4. OCLC 48573453. 
  • Carusi, Cristina, Il sale nel mondo greco, VI a.C.-III d.C.: luoghi di produzione, circolazione commerciale, regimi di sfruttamento nel contesto del Mediterraneo antico (Bari: Edipuglia, 2008) (Pragmateiai; 15).

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