Iodized Salt

“IDD is the single greatest cause of preventable mental retardation. Severe deficiencies cause cretinism, stillbirth and miscarriage. But even mild deficiency can significantly affect the learning ability of populations. Scientific evidence shows alarming effects of IDD. Even a moderate deficiency, especially in pregnant women and infants, lowers their intelligence by 10 to 15 IQ points, with incalculable damage to social and economic development of nations and communities. Today over 1 billion people in the world suffer from iodine deficiency, and 38 million babies born every year are not protected from brain damage due to IDD. These 38 millions, or nearly 30 percent of the world’s newborns, come from families that are the least educated, most isolated and economically disadvantaged. The mark of a civilized society is how well it takes care of its most vulnerable and deprived communities. If we continue to fail to reach these newborns, we will be consigning them to an inter-generational cycle of poverty and injustice.”

– Kul Gautam, Deputy Executive Director, UNICEF, October 2007

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 goiter, 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.

U.S.-goiter-belt

For more than a century, we’ve been aware of the “goiter 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 lack high quality salt manufacturing and packaging technologies. Another is an inadequate regulatory system depriving consumers of confidence that a package labeled “iodized” contains iodine and in the proper amount. Both potassium iodide and potassium iodate are used to add iodine to salt.

 

The technology of iodizing salt

The salt industry plays an indispensible 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.

In the U.S., 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. Although animal feeds are fortified with iodine in the form of potassium iodate, the form most commonly used globally to iodize 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 salt to increase alkalinity, and sodium thiosulfate or dextrose to stabilize potassium iodide. Without a stabilizer, potassium iodide is oxidized to iodine and lost by volatilization from the product.

Outside the U.S. iodine is most commonly added as the more stable potassium iodate and at lower, varying levels.

 

Iodized salt & other additives

Iodine is an essential element in healthy human life enabling the function of our thyroid gland, “the master gland of metabolism.” Too little iodine can produce a thyroid enlargement known as a goiter; more significantly, iodine deficiency impairs fetal brain development and imposes on a newborn infant a lifetime intellectual deficit of 10 – 15 IQ points. Too much iodine is also a problem, though less common.

We ingest iodine with our foods. When we eat seafood, plants grown where soil contains iodine and the meat of animals whose forage grows in such soils, our bodies usually take in enough iodine. But glacial action and natural weathering can leach iodine from the soil leaving it deficient. Plants and animals raised in areas with iodine-deficient soil will be poor sources of iodine in the human diet and the animals themselves will be less healthy and productive.

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 goiter, 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.

David Marine (1880-1976) is the “father” of iodized salt in the United States. As the result of research on endemic goiter and iodine deficiency by Marine and co-workers research, the Michigan State Medical Society, in 1924, launched a goiter prevention program using iodized salt, making iodized salt the first of what we now term “functional foods.”

Medical science since has identified a far more serious threat than the cosmetic problem of goiter — mental retardation. In October 2007, the American Thyroid Association hosted a symposium with valuable current information and capturing the excitement of the progress; it was entitled “A public health triumph in the making.” UNICEF Deputy Executive Director Kul Gautam delivered a stirring charge to delegates that captured not only the moral imperative of universal salt iodization, but included an outstanding historical review of the entire issue. Gautam told delegates:

“IDD is the single greatest cause of preventable mental retardation. Severe deficiencies cause cretinism, stillbirth and miscarriage. But even mild deficiency can significantly affect the learning ability of populations. Scientific evidence shows alarming effects of IDD. Even a moderate deficiency, especially in pregnant women and infants, lowers their intelligence by 10 to 15 IQ points, with incalculable damage to social and economic development of nations and communities. Today over 1 billion people in the world suffer from iodine deficiency, and 38 million babies born every year are not protected from brain damage due to IDD. These 38 millions, or nearly 30 percent of the world’s newborns, come from families that are the least educated, most isolated and economically disadvantaged. The mark of a civilized society is how well it takes care of its most vulnerable and deprived communities. If we continue to fail to reach these newborns, we will be consigning them to an inter-generational cycle of poverty and injustice.”

In the United States, salt producers cooperated with public health authorities and made both iodized and plain salt available to consumers at the same cost. Newspapers urged people to use iodized salt for the prevention of iodine deficiency. The Michigan program was highly successful and iodized salt use quickly spread throughout the country. Ultimately, household use of iodized salt eliminated iodine deficiency in the North America. In 1955, researchers reported that 75.8% of U.S. households used only iodized salt. The Salt Institute estimates that nearly 70% of the table salt sold in the United States is iodized. Virtually none of the salt used in processed foods is iodized, however, so the transformation of eating practices in the U.S. and many other countries, substituting meals prepared outside the homes using plain salt for home-cooked foods containing iodized salt, has led to an erosion of iodine in the U.S. diet. Canada, Australia/New Zealand and much of western Europe long ago addressed the need to ensure availability of iodized salt.

Around the world, however, iodine deficiency remains a major health problem. The Salt Institute has been deeply involved in the International Council for the Control of Iodine Deficiency Disorders (ICCIDD) and, after the salt industry’s Salt2000 Eighth International Symposium on Salt, helped found and continues to provide leadership to The Network for the Sustained Elimination of Iodine Deficiency. Other Network members include ICCIDD, UNICEF, the World Health Organization, Kiwanis International and the Centers for disease control as well as the global salt industry. These groups and national counterparts have made remarkable progress, but even today fully 30% of the households around the world lack access to iodized salt despite the strong, vocal consensus and extremely modest cost.

Salt is hygroscopic; it attracts moisture. Fine grained salt, like table salt, popcorn salt, etc. would fuse together in highly humid conditions, so salt producers in modern salt refineries add any of a number of free-flowing agents to salt. All are, of course, approved food additives by national food safety regulatory agencies (e.g. FDA, in the US). FDA, for example, has approved 18 different additives for salt .

 

Additives used in food salt

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; 1) to enhance the flow properties of salt by preventing the clumping of fine crystals and; 2) 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 vapor from the surrounding environment. When enough water vapor 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.

The Food and Drug Administration requires food grade salt packaging to indicate all additives. Food grade salt in the U.S. 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. A list of permitted additives is shown in the table below. 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 U.S. 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 KI) 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 Food and Drug Administration as an anti-caking additive in table salt based on exhaustive tests demonstrating no evidence of toxicity at levels considerably higher than those used in highway deicing 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.

 

 

 

 

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