Salt

Salt is a dietary mineral essential for animal life, composed primarily of sodium chloride. Salt for human consumption is produced in different forms: unrefined salt (such as sea salt), refined salt (table salt), and iodised salt. It is a crystalline solid, white, pale pink or light grey in color, normally obtained from sea water or rock deposits. Edible rock salts may be slightly greyish in color due to this mineral content.

Chloride and sodium ions, the two major components of salt, are necessary for the survival of all living creatures including humans. Some isolated cultures, such as the Yanomami in South America, have been found to consume little salt, possibly an adaptation originated in the predominantly vegetarian diet of human primate ancestors.^[1] Salt is involved in regulating the water content (fluid balance) of the body. Salt flavor is one of the basic tastes. Salt cravings may be caused by trace mineral deficiencies as well as by a deficiency of sodium chloride itself.

It is believed that over consumption of salt may increase the risk of health problems, including high blood pressure. In food preparation, salt is used as a preservative and as a seasoning.

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History

Main article: History of salt

Common salt (NaCl) has been used for dietary purposes as well as a preservative, a medium of exchange and a source of tax revenue since the ancient times.^[2]

During the times of the historian Herodotus, salt was known along the Libyan desert.^[2] Pliny the elder remarked "Heaven known, a civilised life is impossible without salt."^[3] Pliny lists India, Arabia and Africa as sources for extraction of salt.^[4]

Salt was one of the main marine resources of the Harappans, who may have used a site near the Gulf of Khambat for salt extraction.^[5] Methods of both the salt mining and the procurement by sea were known in ancient India.^[5] Salt mines from ancient India were the center of widespread trade.^[2] Roman soldiers received some of their salaries in form of salt, with the arrangement then known as salarium.^[2] The ancient Mayan civilization also produced salt.^[2] The method of boiling of brine to recover salt was known in Iron Age Europe.^[2]

Japan developed a two step process for concentration and evaporation which has existed since at least 600 CE.^[6] The middle ages saw East Africa develop methods to extract salt from the brine deposits originating in the rift systems.^[7] Elaborate arrangements were made to ensure salt productions, including ditches, storage tanks and the use of various heating techniques.^[7]

In religion

There are thirty-five verses which reference salt in the English translation of the Bible (King James Version), the earliest being the story of Lot's wife, who was turned into a pillar of salt when she disobediently looked back at the wicked cities of Sodom (Genesis 19:26). When King Abimelech destroyed the city of Shechem he is said to have "sowed salt on it;" a phrase expressing the completeness of its ruin. (Judges 9:45.) 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) so that when others enquire about their beliefs, the Christian's answer generates a 'thirst' to know more about Christ.

Salt is mandatory in the rite of the Tridentine Mass. Salt is used in the third item (which includes an Exorcism) of the Celtic Consecration (refer 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.

In the native Japanese religion Shinto, salt is used for ritual purification of locations and people, such as in Sumo Wrestling.

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

Forms of salt

Unrefined salt

Main articles: Sea salt, Halite, and Fleur de sel

  Different natural salts have different mineralities, giving each one a unique flavor. Fleur de sel, natural sea salt harvested by hand, has a unique flavor varying from region to region.

Some advocates for sea salt assert that unrefined sea salt is more healthy than refined salts.^[8] However, completely raw sea salt is bitter due to magnesium and calcium compounds, and thus is rarely eaten. 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.^[9]

Refined salt

  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 industrialised countries (3% in Europe^[10]) although world-wide, food uses account for 17.5% of salt production^[11]. The majority is sold for industrial use. Salt has great commercial value, because it is a necessary ingredient in the manufacturing of many things. 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.^[12] Salt is also obtained by evaporation of sea water, usually in shallow basins warmed by sunlight;^[13] salt so obtained was formerly called bay salt, and is now often called sea salt or solar salt. Today, most refined salt is prepared from rock salt: mineral deposits high in salt.^{[citation needed]} These rock salt deposits were formed by the evaporation of ancient salt lakes.^[14] These deposits 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.

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).^[15] Multiple stages of evaporation are then used to collect pure sodium chloride crystals, which are kiln-dried.     Since the 1950s it has been common to add a trace of sodium hexacyanoferrate II to the brine; this acts as an anticaking agent by promoting irregular crystals.^[16] Other anticaking agents (and potassium iodide, for iodised salt) are generally added after crystallization.^{[citation needed]} These agents are hygroscopic chemicals which absorb humidity, keeping the salt crystals from sticking together. Some anticaking agents used are tricalcium phosphate, calcium or magnesium carbonates, fatty acid salts (acid salts), magnesium oxide, silicon dioxide, calcium silicate, sodium alumino-silicate, and alumino-calcium silicate. Concerns have been raised regarding the possible toxic effects of aluminium in the latter two compounds^{[citation needed]}; however, both the European Union and the United States Food and Drug Administration (FDA) permit their use.^[17] The refined salt is then ready for packing and distribution.

Table salt

Table salt is refined salt, 99% sodium chloride.^[18][19] It usually contains substances that make it free flowing (anticaking agents) such as sodium silicoaluminate or magnesium carbonate. It is common practice to put a few grains of uncooked rice or half a dry cracker (such as Saltine) in salt shakers to absorb extra moisture when anticaking agents are not enough.

Additives

See also: History of iodised salt

Iodized salt (BrE: iodised salt) is table salt mixed with a minute amount of potassium iodide, sodium iodide, or iodate. Iodized salt is used to help reduce the chance of iodine deficiency in humans. Iodine deficiency commonly leads to thyroid gland problems, specifically endemic goiter. Endemic goiter is a disease characterized by a swelling of the thyroid gland, usually resulting in a bulbous protrusion on the neck. While only tiny quantities of iodine are required in a diet to prevent goiter, the United States Food and Drug Administration recommends (21 CFR 101.9 (c)(8)(iv)) 150 micrograms of iodine per day for both men and women, and there are many places around the world where natural levels of iodine in the soil are low and the iodine is not taken up by vegetables.

Today, iodized salt is more common in the United States, Australia and New Zealand than in the United Kingdom. Table salt is also often iodized—a small amount of potassium iodide (in the US) or potassium iodate (in the EU) is added as an important dietary supplement. Table salt is mainly employed in cooking and as a table condiment. Iodized table salt has significantly reduced disorders of iodine deficiency in countries where it is used.^[20] Iodine is important to prevent the insufficient production of thyroid hormones (hypothyroidism), which can cause goitre, 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, iodized salt contains 46-77 ppm, while in the UK the iodine content of iodized salt is recommended to be 10-22 ppm.^[21]

In some European countries where drinking water fluoridation is not practiced, fluorinated table salt is available. In France, 35% of sold table salt contains either sodium fluoride or potassium fluoride.^[22] Another additive, especially important for pregnant women, is Folic acid (Vitamin B9), which gives the table salt a yellow color.

Salty condiments

In many Asian cultures, table salt is not traditionally used as a condiment.^[23]However, condiments such as soy sauce, fish sauce and oyster sauce tend to have a high salt content and fill much the same role as a salt-providing table condiment that table salt serves in western cultures.

Health effects

Sodium is one of the primary electrolytes in the body. All four cationic electrolytes (sodium, potassium, magnesium, and calcium) are available in unrefined salt, as are other vital minerals needed for optimal bodily function. Too much or too little salt in the diet can lead to muscle cramps, dizziness, or even an electrolyte disturbance, which can cause severe, even fatal, neurological problems.^[24] Drinking too much water, with insufficient salt intake, puts a person at risk of water intoxication (hyponatremia). Salt is even sometimes used as a health aid, such as in treatment of dysautonomia.^[25]

People's risk for disease due to insufficient or excessive salt intake varies due to biochemical individuality. Some have asserted that while the risks of consuming too much salt are real, the risks have been exaggerated for most people, or that the studies done on the consumption of salt can be interpreted in many different ways.^{[26] [27]}

Excess salt consumption has been linked to:

• exercise-induced asthma.^[28] On the other hand, another source counters, "…we still don't know whether salt contributes to asthma. If there is a link then it's very weak…".^[29]
• heartburn^[30].
• osteoporosis: One report shows that a high salt diet does reduce bone density in girls.^[31]. Yet "While high salt intakes have been associated with detrimental effects on bone health, there are insufficient data to draw firm conclusions." (^[32], p3)
• Gastric cancer (Stomach cancer) is associated with high levels of sodium, "but the evidence does not generally relate to foods typically consumed in the UK." (^[32], p18) However, in Japan, salt consumption is higher.^[33]
• hypertension (high blood pressure): "Since 1994, the evidence of an association between dietary salt intakes and blood pressure has increased. The data have been consistent in various study populations and across the age range in adults." (^[32] p3). Professor Dr. Diederick Grobbee claims that there is no evidence of a causal link between salt intake and mortality or cardiovascular events.^[34]. One study found that low urinary sodium is associated with greater risk of myocardial infarction among treated hypertensive men ^[35].
• 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." (^[32] p3) "…there is accumulating evidence that high salt intake predicts left ventricular hypertrophy." (^[36], p12) Excessive salt (sodium) intake, combined with an inadequate intake of water, can cause hypernatremia. It can exacerbate renal disease.^[24]
• edema (BE: oedema): A decrease in salt intake has been suggested to treat edema (fluid retention).^[37][24]
• duodenal ulcers and gastric ulcers^[38]

A large scale study by Nancy Cook et al shows that people with high-normal[1] blood pressure who significantly reduced the amount of salt in their diet decreased their chances of developing cardiovascular disease by 25% over the following 10 to 15 years. Their risk of dying from cardiovascular disease decreased by 20%.^[39][40]

Recommended intake

This section summarizes the salt intake recommended by the health agencies of various countries. Recommendations tend to be similar. Note that targets for the population as a whole tend to be pragmatic (what is achievable) while advice for an individual is ideal (what is best for health). For example, in the UK target for the population is "eat no more than 6 g a day" but for a person is 4 g.

Intakes can be expressed variously as salt or sodium and in various units.

• 1 g sodium = 1,000 mg sodium = 42 mmol sodium = 2.5 g salt

United Kingdom: In 2003, the UK's Scientific Advisory Committee on Nutrition (SACN) recommended that, for a typical adult, the Reference Nutrient Intake is 4 g salt per day (1.6 g or 70 mmol sodium). However, average adult intake is two and a half times the Reference Nutrient Intake for sodium. "Although accurate data are not available for children, conservative estimates indicate that, on a body weight basis, the average salt intake of children is higher than that of adults." SACN aimed for an achievable target reduction in average intake of salt to 6 g per day (2.4 g or 100 mmol sodium) — this is roughly equivalent to a teaspoonful of salt. The SACN recommendations for children are:

• 0–6 months old: less than 1 g/day
• 7–12 months: 1 g/day
• 1–3 years: 2 g/day
• 4–6 years: 3 g/day
• 7–10 years: 5 g/day
• 11–14 years: 6 g/day

SACN states, "The target salt intakes set for adults and children do not represent ideal or optimum consumption levels, but achievable population goals."^[32]

Republic of Ireland: The Food Safety Authority of Ireland endorses the UK targets "emphasising that the RDA of 1.6 g sodium (4 g salt) per day should form the basis of advice targeted at individuals as distinct from the population health target of a mean salt intake of 6 g per day."(^[36], p16)

Canada: Health Canada recommends an Adequate Intake (AI) and an Upper Limit (UL) in terms of sodium.

• 0–6 months old: 0.12 g/day (AI)
• 7–12 months: 0.37 g/day (AI)
• 1–3 years: 1 g/day (AI) 1.5 g/day (UL)
• 4–8 years: 1.2/day (AI) 1.9 g/day (UL)
• 9–13 years: 1.5 g/day (AI) 2.2 g/day (UL)
• 14–50 years: 1.5 g/day (AI) 2.3 g/day (UL)
• 51–70 years: 1.3 g/day (AI) 2.3 g/day (UL)
• 70 years and older: 1.2 g/day (AI) 2.3 g/day (UL)^[41]

New Zealand

• Adequate Intake (AI) 0.46 – 0.92 g sodium = 1.2 – 2.3g salt
• Upper Limit (UL)) 2.3 g sodium = 5.8 g salt^[42]

Australia: The recommended dietary intake (RDI) is 0.92 g–2.3 g sodium per day (= 2.3 g–5.8 g salt)^[43]

USA: The Food and Drug Administration itself does not make a recommendation^[44] but refers readers to Dietary Guidelines for Americans 2005. These suggest that US citizens should consume less than 2,300 mg of sodium (= 2.3 g sodium = 5.8 g salt) per day. ^[45]

Labeling

UK: The Food Standards Agency defines the level of salt in foods as follows: "High is more than 1.5g salt per 100g (or 0.6g sodium). Low is 0.3g salt or less per 100g (or 0.1g sodium). If the amount of salt per 100g 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).^[46]

USA: The FDA Food Labeling Guide stipulates whether a food can be labelled 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 480mg of sodium per 'serving.'^[47]

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).^[48] The Advertising Standards Authority did not uphold the SMA complaint in its adjudication.^[49]. 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.^[50]

The Menzies Research Institute in Tasmania, Australia, maintains a website ^[51] dedicated to educating people about the potential problems of a salt-laden diet.

Salt substitutes

Main article: Salt substitute

Salt intake can be reduced by simply reducing the quantity of salty foods in a diet, without recourse to salt substitutes. Salt substitutes have a taste similar to table salt and contain mostly potassium chloride, which will increase potassium intake. Excess potassium intake can cause hyperkalemia. Various diseases and medications may decrease the body's excretion of potassium, thereby increasing the risk of hyperkalemia. If you have kidney failure, heart failure or diabetes, seek medical advice before using a salt substitute. A manufacturer, LoSalt, has issued an advisory statement^[52] that people taking the following prescription drugs should not use a salt substitute: Amiloride, Triamterene, Dytac, Spironolactone (Brand name Aldactone), Eplerenone and Inspra.

Production trends

  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 was estimated at 210 million metric 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).^[53] Note that these figures are not just for table salt but for sodium chloride in general.

See also

• Sodium chloride
• Old Salt Route
• Sea salt
• Smoked salt
• Kosher salt
• History of salt
• Fleur de sel
• Curing (food preservation)
• Salt equivalent
• Black salt
• Pink salt

Notes

References

• Rapp, George Robert; Hill, Christopher L. (2006). Geoarchaeology: The Earth-science Approach to Archaeological Interpretation. Yale University Press. ISBN 0300109660. 

• Ray, Himanshu Prabha; et al. (2003). The Archaeology of Seafaring in Ancient South Asia. Cambridge University Press. ISBN 0521011094.