ZRT Laboratory

International Council for the Control of Iodine Deficiency Disorders

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The Need for Iodine

Iodine is a natural chemical element, like oxygen, hydrogen and iron. It occurs in a variety of chemical forms, the most important being iodide, iodate and elemental iodine. It is present in fairly constant amounts in seawater but its distribution over land and fresh water is uneven. Deficiency is especially common in mountainous areas (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).

Iodine is an essential part of the chemical structure of thyroid hormones. The thyroid is a butterfly-shaped gland in the front part of the neck. It produces two hormones, thyroxine (T4) and triiodothyronine (T3), that are released into the bloodstream and carried to target organs, particularly the liver, kidneys, muscles, heart, and developing brain.

We need iodine because thyroid hormones are essential to life. The thyroid hormones act in target organs by influencing many different chemical reactions, usually involving manufacture of key proteins. The body must have proper levels of thyroid hormone to function well.

Iodine Deficiency

Iodine deficiency is the single most common cause of preventable mental retardation and brain damage in the world. It also decreases child survival, causes goiters, and impairs growth and development. Iodine deficiency in pregnant women causes miscarriages, stillbirths, and other complications. Children with IDD can grow up stunted, apathetic, mentally retarded, and incapable of normal movements, speech, or hearing. Globally, 2.2 billion people (38% of the world's population) live in areas with iodine deficiency and risks its complications.

Iodine deficiency was once considered a minor problem, causing goiter, an unsightly but seemingly benign cosmetic blemish. However, it is now known that the effects on the developing brain are much more deadly, and constitute a threat to the social and economic development of many countries.

Effective and affordable technology exists to prevent iodine deficiency and the problems it causes. The most important are iodized salt and effective monitoring of iodine nutrition.

Iodine and the Brain

Thyroid hormones, and therefore iodine, are essential for normal development of the brain. If a fetus or newborn is not exposed to enough thyroid hormone, it may have permanent mental retardation, even if it survives. The most damaging consequences of iodine deficiency are on fetal and infant development. Maternal iodine deficiency causes miscarriages, other pregnancy complications, and infertility. Low birth weights and decreased child survival also result from iodine deficiency. Cretinism is a very severe degree of this brain damage; it includes permanent dense mental retardation, and varying degrees of additional developmental defects such as deafmutism, short stature, spasticity, and other neuromuscular abnormalities.

The most visible consequence of iodine deficiency is goiter. This word means "an enlarged thyroid." The process begins as an adaptation in which the thyroid is more active in its attempts to make enough thyroid hormone for the body's needs, despite the limited supply of raw material (iodine), much as a muscle gets bigger when it has to do more work. If this adaptation is successful and 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.