Introduction
According to McNeil and Donald (2006), iodized salt is table salt mixed with a minute amount of various salts of the element iodine. The ingestion of iodide prevents iodine deficiency. Worldwide, iodine deficiency affects about two billion people and is the leading preventable cause of intellectual and developmental disabilities. Deficiency also causes thyroid gland problems, including “endemic goitre”. In many countries, iodine deficiency is a major public health problem that can be cheaply addressed by purposely adding small amounts of iodine to the sodium chloride salt.
Iodine is a micronutrient and dietary mineral that is naturally present in the food supply in some regions, especially near sea coasts, but is generally quite rare in the Earth’s crust, since iodine is a so-called “heavy” element (with the highest atomic mass of any element needed by mammals for life), and abundance of chemical elements generally declines with greater atomic mass. Where natural levels of iodine in the soil are low and the iodine is not taken up by vegetables, iodine added to salt provides the small but essential amount of iodide needed by humans. (Michael, B et al., 2005).
Clydesdale and Weimer (1985) state that iodine deficiency is the main cause of preventable brain damage and reduced IQ in children worldwide. It also negatively affects women’s health, as well as economic productivity and quality of life. Most people need an additional source of iodine as it is found in relatively small amounts in the diet. WHO recommends universal salt iodization – the fortification with iodine of all salt used for human and animal consumption – as the main strategy for eliminating iodine deficiency. The public health goals of reducing salt and increasing iodine intake through salt iodization are compatible as the concentration of iodine in salt can be adjusted as needed. Monitoring the levels of iodine in salt and the iodine status of the population are critical for ensuring that the population’s needs are met and not exceeded.
Salt producers are a key partner in combating Iodine Deficiency Disorders (IDD) today throughout the world. Many people erroneously assume that because salt iodization was first implemented nearly a century ago, that the problem no longer exists. Tragically, that’s wrong. In 1990, only about 20% of the world’s households had access to iodized salt and were protected against Iodine Deficiency Disorders. After a major push, access now exceeds 70%. Scientists identified iodine as an element in the early 19th century and only 20 years later, French scientist J-B. Boussingault reported his conclusion that iodized salt would be an effective prophylaxis for goitre, stating “I am convinced that goitre would disappear…if the authorities made available in every district town…a depot of salt containing iodine.” Yet it took another century for “authorities in the U.S. and Switzerland to effectuate Boussingault’s insight (Diosady, 1997).
For more than a century, we’ve been aware of the “goitre belt” in North America. In the United States, from the outset, salt producers cooperated with public health authorities and made both iodized and plain salt available to consumers at the same price. Even so, the Salt Institute estimates that only about 70% of the table salt sold in the United States is iodized.
Salt used in processed foods is not iodized. Given that people are cooking less at home and buying either restaurant or processed foods, iodine intakes in the U.S. have declined from about 250 μg/day to 157 micrograms/day. Public health authorities recommend 150 μg or more and the need is particularly acute for expectant mothers. Daily Iodine intakes of 1,000 – 1,100 μg are safe for adults and children over 4 years of age.
The technology for iodizing or iodating salt is well known, readily available, and inexpensive. One particular problem is that some countries which include Nigeria lack high quality salt manufacturing and packaging technologies. Another is an inadequate regulatory system depriving consumers of confidence that a package labelled “iodized” contains iodine and in the proper amount. Both potassium iodide and potassium iodate are used to add iodine to salt (Nadiger & Krishnamachari 1980).
Conceptual framework
According to Venturi and Venturi (2009), Iodized salt is a form of table salt which has had iodine added to it to prevent a disease called goitre. Goitre is characterized by the swelling of the thyroid gland due to iodine deficiency iodine is a nutrient that usually occurs naturally in vegetables. Which absorb it through the soil in which they grow. But a diet consisting of food grown in soil that lacks iodine can cause an iodine deficiency, leading to goitre.
The practice of adding iodine to salt began in the United States in the 1920s as a way to combat goitre. Salt was chosen as the medium because it is affordable and everyone uses it. Most commercial salt is made from rock salt that comes from underground salt mines. But sea salt, which is harvested by evaporating pools of seawater, is an increasingly popular type of salt. Chemically, sea salt and rock salt are the same, and iodine doesn’t occur naturally in either one. Some manufacturers add iodine to sea salt, just as they do for ordinary iodized salt.
Iodized salt is so ubiquitous that we barely notice it. Few people know why it even exists. Iodine deficiency remains the world’s leading cause of preventable mental retardation. According to a new study, its introduction in the early 1920s had an effect so profound that it had raised the world’s intelligent quotient (lQ) (Knudsen et al., 2002).
A new working paper from James Feyrer, Dimitra Politi, and David N. Weil finds that the population in iodine-deficient areas saw lQs rise by a full standard deviation, which is 15 points, after iodized salt was introduced. According to the working paper, lQs has continue to go up by about 3 points every decade, so iodization of salt may be responsible for a full decade’s worth of increasing IQ in the world.
According to World Health Organisation (2007), if a mother is iodine deficient while she’s pregnant, the cognitive development of the foetus is impeded, and the effects are irreversible. To this day, the World Health Organization estimates that nearly 50 million people suffer some kind of mental impairment related to iodine deficiency.
In addition, WHO stated that before iodized salt, people were deficient based almost entirely on geography, whether the water and soil in their area had enough of the micronutrient. Diseases resulting from the deficiency, most commonly goitre, or swelling of the thyroid, were extremely common. The differences by geography were vast, making the effects easy to isolate. Seawater, for example, is rich in iodine, but there are areas which are known for iodine depletion due to the occurrence of glacier for example Michigan in the United States and Alberta in Canada.
The technology of iodised salt
The salt industry plays an indispensable role in the global campaign against Iodine Deficiency Disorders by producing iodized salt. Modern salt plants routinely spray potassium iodide or potassium iodate onto the salt while it moves along a conveyor belt before it is packaged. In lower-tech operations, iodine is sometimes added as a dry ingredient and physically mixed with the salt. Generally, iodized salt contains 0.002% to 0.004% iodine, supplied either as potassium iodide or potassium iodate.
Apart from the general iodized salt content of 0.002% to 0.004%, some countries for example the United States of America, iodine is added as potassium iodide in table salt at slightly higher levels 0.006% to 0.01% potassium iodide, equivalent to 0.0046% to 0.0077% iodine. Potassium iodide is one of two sources of iodine permissible by the U.S. Food and Drug Administration (FDA). Although animal feeds are fortified with iodine in the form of potassium iodate, the form most commonly used globally to iodized food salt outside the U.S. because of its greater stability, FDA does not approve potassium iodate to fortify food salt in the U.S. Therefore, U.S. salt producers add sodium carbonate or sodium bicarbonate when they iodize saIt to increase alkalinity, and sodium thiosulphate or dextrose to stabilize potassium iodide. Without a stabilizer, potassium iodide is oxidized to iodine and lost by volatilization from the product (Patrick, 2008). In Nigeria, iodine is most commonly added as the more stable potassium iodate and at lower, varying levels to that of the U.S. but within the genera’ range of 0.002% to 0.004%. (NAFDAC, 1999).
Additives used in table salt
Andersson et al. (2005) in their report to the World Health Organization stated that additives perform a wide variety of useful functions including those that are often taken for granted. In salt, additives are used for two main purposes;
- To enhance the flow properties of salt by preventing the clumping of fine crystals and;
- To fortify salt with iodine in order to prevent iodine deficiency diseases.
Salt crystals are tiny cubes with flat surfaces that have a tendency to stick together. In addition, salt is hygroscopic, which means that the crystals absorb water vapour from the surrounding environment. When enough water vapour is absorbed, it changes into a liquid form and partially dissolves the salt surface layer, which further encourages the crystals to clump together. This prevents the free flow of salt from the shaker and clogs up the holes, thereby preventing salt from being dispensed. Anti- caking agents are added in order to ensure that salt remains free-flowing. Fine crystallized salt, such as sea salt, that does not contain these anti- caking agents is particularly prone to this problem.
Food grade salt in the must comply with the Food Chemicals Codex Sodium Chloride Monograph (2008) which specifies that salt may contain up to 2% of suitable food-grade anti-caking, free-flowing, or conditioning agents. Although the total amount of additives that can be added to salt is 2%, in reality far less is generally used. (Most table salt labels typically indicate that they are more than 99% pure sodium chloride.).
In order to prevent iodine deficiency diseases, more than half of the table salt sold in the world today is iodized and is available at the grocery store at the same price as plain salt. Potassium iodide is added at levels of 0.006 to 0.010% (as Kl) and has proven to be exceptionally effective during the course of the last 85 years. Dextrose, when added (typically at about 0.04%), acts as a stabilizer for potassium iodide in salt, preventing it from disassociating into “free” iodine, which may be lost from the salt through simple vaporization. When combined with good packaging, these additives ensure that iodized salt retains its ability to combat iodine deficiency disorders, even while remaining in the kitchen pantry for long periods of time.
Anti-caking agents are also added to salt used for de-icing. Although de-icing salt is typically a very coarse particle size, it usually contains a small proportion of fine crystals, which cause clumping. This phenomenon is exacerbated by the salt’s continual exposure to humidity and precipitation. The most frequently used additive is sodium ferrocyanide, also known as Yellow Prussiate of Soda (YPS). Another is ferric ferrocyanide, also known as Prussian Blue. They are added in amounts of 20 to 100 ppm.
YPS is approved by the World Health Organisation as an anti-caking additive in table salt based on exhaustive tests demonstrating no evidence or toxicity at levels considerably higher than those used in highway de-icing salts. Prussian Blue is also used in household bluing, blueprints, blue-black ink and carpenter’s chalk and is also non-toxic to animal and plant life.
Why iodine is added to table salt
Iodine first began being added to salt commercially in the United States in 1924 by the Morton Salt Company at the request of the government. This was done as a response to the fact that there were certain regions in the U.S., such as around the Great Lakes and in the Pacific Northwest, where people were not getting enough iodine in their diets due to it not being prevalent in the soil in those regions. Among other problems, this caused many people to develop goitres (swelling of the thyroid gland).
About 90% of people who develop goitre do so because of a lack of iodine in their diets, so the simple solution was to add iodine to something pretty much everyone consumes fairly regularly, namely salt. This practiced was not thought up by the U.S., but was copied from the Swiss who were adding iodine to salt at this time for the same reason. This resulted in researchers at the University of Michigan testing this practice out with good results and subsequently Morton Salt Company adopting the practice on a national level.
For reference, the World Health Organisation recommends that you consume about 150 micrograms of iodine per day and, on average, men gets about double that amount per day and women each consume about 210 micrograms of iodine per day. Your thyroid itself only needs about 70 micrograms per day to function properly.
Even though most people get plenty of Iodine in their diets, because Iodine is so critical to our bodies functioning properly and the Tolerable Upper Intake Level is so high (about 1100 micrograms per day, and you would not take a fatal dose unless you ingest about 2 million micrograms, or 2 grams), adding it to salt is still recommended by many government health agencies the world over to stave off certain health problems.
Specifically, Iodine is a critical element used by your thyroid in being able to synthesize certain gland secretions which, among other things, influences your heart, metabolism, nerve responses, etc. Further, a lack of iodine during pregnancy and in the baby’s diet after being born can cause a myriad of significant health and developmental problems. Iodine deficiency has also been linked to increased difficulty with information processing, diminished fine motor skills, extreme fatigue, depression, weight gain, and low basal body temperatures, among other things, (Felig & Frohman 2001).
Health consequences of iodine deficiency
Qian and Watkins (2005) stated that there are two major health consequences of iodine deficiency in humans usually referred to as Iodine Deficiency Disorders (IDD). They are;
- Goitre
- Cretinism
Goitre: This is caused by a low amount of thyroxin (one of the two thyroid hormones) in the blood, due to lack of dietary iodine to make it, gives rise to high levels of thyroid stimulating hormone (TSH), which stimulates the thyroid gland to increase many biochemical processes; the cellular growth and proliferation can result in the characteristic swelling or hyperplasia of the thyroid gland, or goitre. In mild iodine deficiency, levels of triiodiothyronine (T3) may be elevated in the presence of low levels of levothyroxine, as the body converts more of the levothyroxine to triiodothyronine as a compensation. Some such patients may have a goiter, without an elevated TSH.
Cretinism: This is referred to as a preventable mental handicaps worldwide, producing typical reduction in IQ of 10 to 15 IQ points. It has been speculated that deficiency of iodine and other micronutrients may be a possible factor in observed differences in IQ. Cretinism is a condition associated with iodine deficiency, commonly characterised by mental deficiency, deaf-mutism, squint, disorders of stance and gait, stunted growth and hypothyroidism.
Treatment of iodine deficiency disorders
Iodine deficiency is treated by ingestion of iodine salts, such are found in food supplements. Mild cases may be treated by using iodized salt in daily food consumption, or drinking more milk, or eating egg yolks, and saltwater fish. For a salt and/or animal product restricted diet, sea vegetables may be incorporated regularly into a diet as a good source of iodine. The recommended daily intake of iodine for adult women is 150-300 µg for maintenance of normal thyroid function; for men it is somewhat less at 150 µg. (Max, 2013).
References
Andersson, M.; Thankachan, P.; Muthayya, S.; Goud, R.B.; Kurpad, A.V.; Hurrell, R.F. & Zimmermann, M.B. (2005). Dual fortification of salt with iodine and iron: a randomized, double-blind, controlled trial of micronized ferric pyrophosphate and encapsulated ferrous fumarate in southern India. Am J Clin Nutr. Nov;88(5):1378–87.
Bunmi, A. D. & Nduka, H. (2003). Knowledge, Beliefs and Practices Regarding Iodine Deficiency Disorders among Children in Arochukwu Nigerian Pediatrics Journal;65:115–20.
Clydesdale, F. Weimer, K.(1985). Iron Fortification of Foods. Food Science and Technology: A Series of Monographs, Academic Press Inc., Harcourt Brace Jovanovich, Publishers, 1-176.
Diosady, L. (1997) – Stability of Iodine in Iodized Salt Used for Correction of Iodine Deficiency Disorders – Food and Nutrition Bulletin Vol. 18(4) pp 388-96.
Felig, B. O & Frohman, P. (2001). Short-term effectiveness of mandatory iodisation of table salt at an elevated iodine concentration, on the iodine and goitre status of school children with endemic goitre. Am J Clin Nutr;71:75–80.
Food Chemicals Codex Sodium Chloride Monograph (2008). Unfulfilled potential: using diethylcarbamazine-fortified salt to eliminate lymphatic filariasis. FCCSCM; Alberta.
Knudsen, B.; Bartalena, L.; Bogazzi, F,; Pecori, F. & Martino, E.(2002). Graves’ disease occurring after thyroiditis. Report of a caseand review of the literature. Thyroid;6(4):345–348.
Max, N. (2013). “How Adding Iodine To Salt Resulted In A Decade’s Worth Of IQ Gains For The United States”. Business Insider.
McNeil, J. & Donald, G. (2006). “In Raising the World’s I.Q., the Secret’s in the Salt”. New York Times. New York. United States.
Michael, B. Isabelle, A. Toni, T. & Hans, B. (2005). “Increasing the iodine concentration in the Swiss iodized salt program markedly improved iodine status in pregnant women and children: a 5-year prospective national study”. American Journal of Nutrition Vol. 82 (2) pp 388–392.
Nadiger, H. & Krishnamachari, K. (1980). The Use of Common Salt (Sodium Chloride) Fortified with Iron to Control Anaemia: Results of a Preliminary Study. British Journal of Nutrition Vol. 43, pp 45-51.
NAFDAC (1991). A Review on Standardization of Iodine Requirement in Salt Manufacturing; NAFDAC; Abuja.
Patrick G. R. (2008). Monitoring Universal Salt Iodization Programmes ICCIDD: Atlanta Georgia USA, & Ottawa Canada.
Qian, K. & Watkins, E. (2005).Elimination of iodine deficiency disorders by 2000 and its bearing on the people in a district of Orissa, India: a knowledge-attitude practices study. Asia Pacific J Clin Nutr;10(1):58–62.
Venturi, P.L. & Venturi, K.E. (2009) Knowledge of Iodine Nutrition in the South African Adult Population. Public Health Nutrition; 8(4):382–6.
World Health Organisation (2007). Safe Use of Iodised Salt to Prevent Iodine Deficiency in Pregnant Women. Update. Bull World Health Organ;74(1):1–3.
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