Frequently Asked Questions
What is iodine?
Iodine is a chemical element (as are oxygen, hydrogen, and iron). It occurs in a variety of chemical forms, the most important being: iodide (I-); iodate (IO3-), and elemental iodine (I2). It is present in fairly constant amounts in seawater but its distribution over land and fresh water is uneven. Deficiency is especially associated with high new mountains (e.g., Himalayas, Andes, Alps) and areas of frequent flooding, but many other areas are also deficient (e.g., Central Africa, Central Asia, much of Europe).
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What does iodine do and why do we need iodine?
Iodine is needed by the body for the production of hormones. These hormones are manufactured by the thyroid gland and are therefore commonly known as thyroid hormones. The thyroid is a butterfly-shaped gland in the front part of the neck. It makes two hormones (thyroxine (T4) and triiodothyronine (T3)). The thyroid hormones are released into the bloodstream and carried by it to target organs, particularly the liver, kidneys, muscles, heart, and developing brain, where they influence many different chemical reactions, usually involving manufacture of key proteins. The body must have proper levels of thyroid hormone to work well.
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How much iodine should we get?
Several international groups have made recommendations, which are fairly similar. ICCIDD, WHO, and UNICEF recommend the following daily amounts: age 0-7 years, 90 micrograms (mcg); age 7-12 years, 120 mcg; older than 12 years, 150 mcg; and pregnant and lactating women, 200 mcg.
A recent report by the Food and Nutrition Board, Institute of Medicine, National Academy of Sciences, USA, offers similar recommendations. It calculates an "Estimated Average Requirement" and from that derives an RDA (Recommended Daily Allowance). However, occasionally sufficient data are not available and instead an "Adequate Intake" is calculated, which may be set higher than the RDA would be, for safety. The recommendations for daily intake are as follows: the AI for infants 0-6 months is 110 mcg iodine and 7-12 months, 130 mcg; the RDA's are: 1-8 years old, 90 mcg; 9-13 years, 120 mcg; 14 and older, 150 mcg; pregnancy, 220 mcg; lactation, 290 mcg. The Food and Nutrition Board also sets the tolerable upper limits of the daily iodine intake as 1.1 mg (1100 mcg) for adults, with proportionately lower levels for younger age groups.
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Where do we get iodine from?
Most of it comes from what we eat and drink. Seafood is usually a good source because the ocean contains considerable iodine. Freshwater fish reflect the iodine content of the water where they swim, which may be deficient. Other foods vary tremendously in iodine content, depending on their source and what may have been added. Plants grown in iodine-deficient soil do not have much iodine, nor do meat or other products from animals fed on iodine-deficient plants. Because the breast concentrates iodine, dairy products are usually a good source, but only if the cows get enough iodine.
Iodized salt is a special case. With only a few isolated exceptions, edible salt (sodium chloride) does not naturally contain iodine. Iodine is added deliberately as one of the most efficient ways of improving iodine nutrition. The amount added varies widely in different regions. In Canada and the United States, iodized salt contains 100 ppm (parts per million, same as 100 mcg/gram) as potassium iodide (equals 77 ppm as iodide), so two grams of salt contains approximately the daily recommended amount of 150 mcg iodine. In the United States, you can buy salt that is either iodized or not iodized, and the price is the same; about 50% of all the salt sold in the U.S. is iodized. In Canada, all table salt is iodized. Most other countries add from 10 to 40 mcg iodine per gram of salt (10-40 ppm). Daily salt intake varies greatly in different parts of the world, ranging from two to five grams in many western countries to 20 grams in some others. An average figure may be 10 grams per day.
These statements apply only to table salt. Most edible salt is added at cooking. If present as potassium iodate, as in most countries, little iodine is lost during cooking, depending on how pure the salt is. Many people get most of their salt from processed foods, especially in developed countries, and commercial practices vary as to whether these contain iodine or not.
Iodine exposure can come from many other sources. Certain food colorings (e.g., erythrosine) contain iodine, although it is only partially bioavailable. Some iodine from skin disinfectants, such as povidone iodine, is absorbed and reaches the bloodstream. Certain health foods, such as some types of kelp, contain large amounts of iodine. Other sources are dyes used for contrast in X-ray procedures and medicines, such as Amiodarone (used for heart failure and abnormal heart rhythm). People also get iodine from its use in farm animals, for cleansing udders or as part of iodine-containing medicines. Iodate has been used as a bread stabilizer in commercial baking, although this practice is less common now. Many other environmental sources of iodine exist; most of them are unrecognized or unpublicized.
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What happens if we don't get enough iodine?
When the diet contains insufficient iodine, the thyroid gland cannot make enough thyroid hormone to satisfy the body’s need. The thyroid gland becomes enlarged due to its desperate efforts to produce the hormone; this enlargement is known as goiter (This word means "an enlarged thyroid".), which is a swelling in the neck (just below adam's apple or larynx), the outward sign of iodine deficiency. Although the most common cause for goitre in the world is iodine deficiency, it is also associated with Hashimoto's thyroiditis, Graves-Basedow disease, juvenile goiter, neoplasm of the thyroid, thyroiditis (acute, chronic), and side-effects of pharmacological therapy. While the goitre formed by the enlargement of the thyroid gland is unsightly and can, if too large, interfere with well-being and even cause problems in respiration, the real danger of iodine deficiency lies in the fact that there is not enough thyroid hormone for the body’s multiple needs. The damage done by this lack of thyroid hormone varies in severity depending on the time in life at which the deficiency occurs.
If the iodine deficiency is not too severe, the person may escape with only an enlarged thyroid and no other apparent damage from the iodine deficiency. Older individuals with goiters may develop nodules (lumps) in their thyroids, and sometimes these can begin making too much thyroid hormone when suddenly exposed to iodine. This result occurs because these nodules are independent of usual controls; they make thyroid hormone at their own rate, and may over-produce it when given more iodine. Also, the nodular goiters in iodine deficiency have an increased rate of one type of thyroid cancer, called "follicular cancer." Goiters can sometimes enlarge enough to produce compression of other neck structures and may need surgical removal for that reason.
In addition to these effects on the individual, iodine deficiency has adverse consequences for the community. The mental retardation can cover a wide range, from mild blunting of intellect to cretinism, and a large part of the population may have some intellectual impairment. The mean IQ of the deficient community is decreased by about 13.5 IQ points, according to one review. Individuals in these communities have lower educability and lower economic productivity, and the output of the whole community suffers. Dramatic improvement typically occurs after appropriate addition of iodine.
The brain is particularly sensitive to iodine deficiency during its formation in early fetal and postnatal life. Also, physical growth and psychomotor development are most severely affected in early life and youth. Iodine is therefore essential for women of childbearing age, because the damage done to the brain in early pregnancy can occur before the woman is even aware that she is pregnant. Maternal iodine deficiency causes miscarriages, other pregnancy complications, infertility, congenital anomalies, mental retardation and all forms of growth retardation. All these together are called iodine deficiency disorders, or IDD. The manifestations of IDD are most severe during pregnancy and infancy. The effects however persist into later life.
The most extreme form of iodine deficiency disorder is cretinism. The effect of IDD on mental development does not however always lead to severe mental retardation or cretinism; it includes permanent dense mental retardation, and varying degrees of additional developmental defects such as deafmutism, short stature, spasticity, and other neuromuscular abnormalities. The more common effect is a reduction in learning capacity. Studies have shown that iodine deficient children have intelligence quotients or IQs that are 10–15 points lower than those of children who do not suffer from IDD. This has grave consequences for their intellectual development, and for the development of their communities and their countries. An iodine deficient people cannot produce as much as they should, they cannot learn as well as they should, with disastrous effects on economic development.
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What happens if we get too much iodine?
Most people who have previously been iodine sufficient can safely tolerate fairly large amounts. As mentioned above, some individuals have thyroid nodules that escape the body's usual controls, and they can start making too much thyroid hormone when their dietary iodine increases, to produce a condition called iodine-induced hyperthyroidism.
Iodine excess can also cause thyroid underactivity, because large amounts of iodine block the thyroid's ability to make hormone. Individuals vary widely in their tolerance to iodine. Most people can handle large amounts satisfactorily, but there are exceptions. People with a tendency towards so-called autoimmune thyroid diseases, such as Graves' disease or Hashimoto's thyroiditis, or who have family members with these problems, may be more sensitive to iodine. In fact, high iodine intakes in a population are associated with an increased incidence of these autoimmune thyroid diseases. Also, high levels of iodine in the population may increase the incidence of papillary thyroid cancer, although this is not well established. Fortunately, papillary thyroid cancer is usually a mild form of cancer and rarely causes death.
Most people can tolerate at least 1 mg (1000 mcg) of iodine daily without adverse effects. People with underlying autoimmune thyroid disease or who have previously been iodine deficient, may tolerate less. Iodine excess is undesirable, but its consequences are not nearly so severe as those of iodine deficiency, because the latter affects human development and can produce permanent brain damage. Properly iodized salt will rarely add more than about 300 mcg iodine daily to the diet. Therefore, concern about iodine excess is not a reason to stop or avoid consumption of iodized salt.
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How can we tell if we are getting the right amount of iodine?
Usually you as an individual won't know how much iodine you are getting, particularly in countries like the United States, because iodine appears in commercial preparations without notice. You can make a rough calculation, based on (1) whether you use iodized salt; (2) how much salt you eat; (3) whether you take vitamins that contain iodine (many contain 150 mcg); and (4) whether you eat much meat, dairy products, or seafood.
For populations, a better way to learn the iodine intake is to measure the amount of iodine in representative urine samples. Most (more than 90%) of the iodine you ingest eventually comes out in the urine. Thus, the concentration of iodine in the urine, even in casual samples, is a good marker for iodine nutrition. Urine iodine concentration varies with fluid intake, so these ranges have limited use for casual samples from an individual, but they are good for assessing a population group, because individual variations tend to average out. A median urinary iodine concentration between 100 and 200 mcg/L is ideal. The following scale has been used by WHO/ICCIDD/UNICEF to relate iodine nutrition to urinary iodine concentration:
Median Urinary Iodine Concentration (µg/L) Corresponding Approximate Iodine Intake (µg/day) Iodine Nutrition
<20 <30 Severe deficiency
20-49 30-74 Moderate deficiency
50-99 75-149 Mild deficiency
100-199 150-299 Optimal
200-299 300-449 More than adequate
>299 >449 Possible excess
Routine laboratory tests of thyroid function are not as helpful as the urinary iodine concentration in assessing a population. The serum TSH (thyroid stimulating hormone or thyrotropin) is a test that is widely used clinically to assess thyroid function in individuals. TSH is released into the blood stream by the pituitary (an endocrine control gland at the base of the brain) in response to the amount of thyroid hormone in the blood stream. TSH tells the thyroid how hard to work. It bases this decision on how much thyroid hormone is present in the blood. When blood thyroid hormone is low, serum TSH increases and this can be used as a measure for inadequate thyroid hormone production. The serum TSH is the most widely used test for diagnosing thyroid disease in individuals. However, the serum TSH is less valuable in recognizing iodine deficiency, because it can increase but still remain within the normal range.
An exception is the blood TSH in newborns. Most developed countries have a system of newborn screening, either with the blood TSH or thyroxine, to recognize congenital hypothyroidism. About one out of 4,000 newborns has congenital deficiency of thyroid hormone production, usually because the thyroid is absent or fails to develop properly. This newborn screening is important because prompt treatment with thyroid hormone can prevent most or all of the consequences of inadequate thyroid hormone on brain development. Newborn TSH screening in areas with iodine deficiency shows an increase in the number of infants with transient hypothyroidism. Usually, this transient hypothyroidism corrects itself, and most of these infants do not show brain damage, but there remains a potential risk for this result, particularly if they continue iodine deficient during nursing.
Thyroid size is also a useful marker of iodine nutrition, because the iodine-deficient thyroid enlarges, as described above. One way to recognize goiter is to feel the thyroid and make an estimate of its size; this maneuver is quite simple but fairly crude and not very accurate in detecting slight enlargement, particularly in children. Use of an ultrasound machine is simple and can be done in remote settings; this measurement provides another good index of the degree of iodine deficiency.
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How do we adjust iodine nutrition?
Salt is the best vehicle for adding iodine. Everyone needs salt, everyone eats it, usually in daily amounts, and the technology for iodization is straightforward. It can be added as potassium iodide or potassium iodate; the latter is preferred under conditions of humidity or impurities because of its greater stability. Most countries have regulations calling for 20-40 mcg iodine/g of salt (20-40 ppm); thus if an individual eats 5 g of salt iodized at 30 ppm, she gets 150 mcg iodine from this source alone. The amount to be added varies for particular populations, depending on the amount of salt ingested, the purity of the salt (and therefore, the amount lost between production and consumption), and the amount of iodine ingested from other sources. In some countries, when daily salt intake decreases, the health authorities raise the amount of iodine in the salt, to provide a constant adequate daily amount.
Another method for providing iodine to a community is through the administration of iodized vegetable oil. These preparations, e.g., Lipiodol, were developed as an X-ray contrast medium. One milliliter (one-fifth of a teaspoon) contains about 480 mg of iodine. A single administration orally provides adequate iodine for about a year, and if given by intramuscular injection, is satisfactory for about three years. Iodized oil is most useful when the iodine deficiency is severe, when immediate correction is important, and when iodized salt is not yet available.
Drinking water is another occasional vehicle for iodine nutrition. Some systems slowly release iodine from a porous basket (containing a concentrated iodine solution) into well water. Another approach adds an iodine solution to water in a well or flowing through a pipe. A simpler version merely adds a few drops of a concentrated solution manually to vessels containing drinking water in a school or home. If iodine (I2) is added, it can also sterilize the water; this property is useful because many regions with iodine deficiency also have contaminated food and water.
Occasionally, iodine is given as tablets of potassium iodide, from 100 to 300 mcg per day or about 1 mg per week. Some vitamin/mineral preparations for daily use contain 150 mcg iodine, the recommended amount.
Other vehicles like sugar, bread, and tea have been occasionally used for iodine delivery. However, the many advantages of iodized salt make it the overwhelming favorite for most countries.
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IDD in the world
This process of leaching away of iodine still continues, and due to ongoing erosion, iodine deficiency affects more and more countries in the world. The iodine which was washed away by glaciers, floods and erosion ultimately ended up in the sea, which is therefore rich in iodine. As a result, seafood contains iodine, especially seaweed, which accumulates iodine. All crops grown on soils that are iodine deficient will be iodine deficient. Iodine deficiency is therefore a deficiency which can affect rich and poor countries alike, because it depends on the geophysical properties of the land, on the way in which the land is formed, the age of its mountains and on whether there are mountains or flood plains.
The World Health Organization (WHO) has for the past few decades kept track of the spread of IDD through the world. While IDD is of course not a contagious disease, there are changes in the numbers of people affected as well as the countries where IDD is found, for two main reasons. First, many countries have taken measures to prevent IDD from occurring, so their populations do not suffer any more from IDD; second, as a result of better techniques in detection and possibly related to rampant erosion, more and more countries are found to have populations suffering from IDD. In 1960, WHO estimated that 200 million people in the world were suffering from goitre. In 1992, this figure was raised to at least 655 million people worldwide who were suffering from goitre, in 110 countries. The number of people suffering from goitre is however only part of the problem. Many more are at risk. In 1987, WHO estimated that 800 million people worldwide were at risk of IDD, an estimate that has now gone up to more than 1000 million.
In the Eastern Mediterranean Region, which encompasses 22 countries, extending from Morocco in the west to Pakistan in the east, at least 16 countries have a problem with IDD. Over 42% of the total population of the region is considered at risk of IDD—that means 173 million people. The countries where IDD is most severe are the mountainous countries in the east, but surveys carried out in the past five years in most countries of the Region showed that IDD affects many more countries and many more people in those countries than previously thought.
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IDD in history
The oldest reports about iodine deficiency and more specifically goitre come from China. As much as 5000 years ago, Chinese authors described goitre, for which they prescribed seaweed. Nowadays it is known that people who eat a lot of seaweed do not suffer from iodine deficiency. For instance the Japanese, who consume a great deal of seaweed, as well as other seafood, do not suffer from IDD. In the Middle Ages, iodine deficiency was very common in Europe. In the Alps, in Switzerland for instance, cretins were a common sight. IDD was in fact so common in Europe that painters depicted women with goitres as a sign of beauty. Not only were the mountainous regions of Europe affected by IDD, but so were countries like the Netherlands, much of which is located below sea level and thus can be considered as a flood plain.
Goitre and other manifestations of iodine deficiency must also have existed in the Eastern Mediterranean Region, and there are in fact suggestions that Cleopatra had a goitre.
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What is being done internationally about iodine deficiency?
The International Council for the Control of Iodine Deficiency Disorders (ICCIDD) came into existence in 1985 with the single purpose of achieving optimal iodine nutrition worldwide. It has worked closely with UNICEF and the World Health Organization towards this objective. These and other early efforts led to a pledge by the World Summit for Children, in 1990, to achieve the virtual elimination of iodine deficiency. A massive effort has taken place during the past decade. Key players have included governments and citizens in countries, the salt industry, UNICEF, WHO, ICCIDD, and the Micronutrient Initiative, with major funding from Kiwanis International, the World Bank, the aid programs of Canada, Australia, the Netherlands, and the United States, and many others. Universal salt iodization is the main strategy. Currently, about 70% of households worldwide consume iodized salt. Some countries with previously severe iodine deficiency now appear to be virtually sufficient; e.g., China, Nigeria, Congo, Iran, Peru, Ecuador, and Thailand. This success involves not only the implementation of iodized salt, but effective national programs, the development of national IDD coordinating groups, extensive education at all levels, and monitoring. The current emphasis is now on iodine nutrition in those parts of the world that are still lagging, particularly in Central Asia and Africa, and on maintaining the progress made in other countries.
In May 2000, at the World Salt Symposium (“Salt 2000”) in The Hague, executives of the salt industry met with leaders of governments, NGOs, and international organizations. At issue was the question of how to better collaborate to accelerate global progress towards ending iodine deficiency forever. An agreement was reached to form a global coalition of public, private, international and civic organizations. The goal of this global organization would be to harmonize and support activities that assist countries in reaching the goal of sustained IDD elimination through universal salt iodization. This global organization is known today as the Network for Sustained Elimination of Iodine Deficiency.
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How can countries maintain optimal iodine nutrition?
In areas with previous iodine deficiency, the key point is monitoring, both of iodine levels in people (by urinary iodine) and in salt. It is recommended that countries have regular monitoring by urinary iodine in representative subgroups of the population every several years, with mandatory publication of the information, and prompt corrective action when deviations occur. Regular quality control of the iodine levels in salt, when that is the vehicle, is also essential. Some part of the government - usually the Ministry of Health or a national coordinating body - needs to take responsibility and be provided adequate resources for the program. Everyone involved - citizens, government, salt producers, agencies, the health sector - needs to be aware, so an active education campaign is a key part of a successful program.
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What can people themselves do to prevent IDD and its consequences?
IDD cannot be eliminated without the active participation of the people themselves. Everyone who lives in a country or area where the soil is deficient in iodine is at risk of IDD. Even in countries were the problem is not very severe, the risk of intellectual impairment is real. To prevent IDD and to have bright and intelligent children, every parent should ensure that only iodized salt is consumed by the family, every day. There is no need to start eating more salt; in fact this is dangerous. Just eating iodized salt instead of non-iodized salt, in the same quantities as usual, is enough to prevent IDD.
It is important to remember that the salt producers and the government are doing their best to ensure that the salt contains adequate amounts of iodine. Therefore, the consumer has the responsibility to ensure that the salt, once purchased is kept in a tightly closed container, to protect it from humidity and sunlight which can destroy the iodine. Iodized salt should be used in cooking and at the table. There is no need to have any other salt in the house. Iodized salt tastes and looks the same as non-iodized salt. The only way in which the consumer can see the difference is by looking on the label of the salt packet when buying the salt.
Iodized salt is not harmful for people who already consume enough iodine. However, sea salt, believed by many to contain “natural” iodine, does not contain a sufficient quantity.
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IDD has been called a scourge of humanity. It not only causes goitre, but may result in irreversible brain damage in the fetus and infant, and retarded psychomotor development in children. Iodine deficiency is the most common cause of preventable mental retardation. The effects of iodine deficiency on a country’s population have a negative impact on the entire economy of affected nations. Fortunately, there is a simple and cheap way of preventing iodine deficiency and that is through the provision and consumption of adequately iodized salt. Together, consumers, producers and governments can protect themselves and their children against the terrible consequences of iodine deficiency.
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