Iodine was one of the first essential micronutrients to be discovered. Its sole known purpose in the human body is as a major component in the production of thyroid hormone. Thyroid hormone plays an essential role in protein synthesis and is critically important for neuronal development and optimum function of the central nervous system.
The degree of effect on the nervous system depends on the severity of the deficiency and its timing in relation to fetal and childhood central nervous system development.
The signs and symptoms of iodine deficiency have been known for many years. The most prevalent is goiter, a diffuse enlargement of the thyroid gland. As the body attempts to compensate for the lack of iodine, thyroid tissue increases to make maximal use of available iodine in order to manufacture thyroid hormone. Large goiters can cause disfigurement and partial obstruction of the airway and esophagus. More importantly iodine deficiency and subsequent hypothyroidism can interfere with development and function of the central nervous system. This effect is most critical during the second trimester of fetal development, when maternal iodine deficiency produces severe irreversible damage to the fetal brain. The child is subsequently born with a condition called cretinism, a combination of severe mental deficiency, deaf-mutism and awkward gait. Cretinism cannot be treated with iodine or any other means, but can be prevented by treating the mother with iodine during the early stages of pregnancy. What has been more recently identified is a much more widespread and more subtle but irreversible decrease in mental function caused by a moderate to severe iodine deficiency during the critical stages of continued brain development during early childhood. Mental delays can also be documented due to iodine deficiency in later childhood and into adult life. Fortunately the latter can be reversed by sustained treatment with iodine. Iodine deficiency occurs mainly in mountainous regions of the world, such as in the Himalayas, the Alps, the Andes, and the Highlands of Central America, where the soil has been leached of its iodine content through years of flooding, glaciation, and erosion. Some lowland areas in Africa, and in the US Great Lakes Region are also iodine depleted. The incidence of goiter in these regions may reach 30% or more in the absence of iodine supplementation. In some villages in Nepal the incidence of Cretinism may be as high as 25%. It is estimated by WHO that 2 billion people, 1/3 of the world’s population, are at risk for iodine deficiency. A simple means of assessing deficiency is the measurement of iodine in the urine. Treatment is also relatively simple using iodinated oil or Lugol’s solution, but must be continued for a prolonged period of time. It is far more preferable to prevent the deficiency by regular iodine supplementation in the diet. Iodized salt has been recognized as an ideal supplement for over 80 years. The manufacturing process is simple and costs a few pennies per person per year. Yet for reasons that remain obscure programs were not put in place outside of the US and Europe for many decades. As of 1990, according to WHO estimates, 20 million children had varying degrees of preventable brain damage due to iodine deficiency. At this time a worldwide effort known as the Global Network for the Sustained Elimination of Iodine Deficiency was formed under WHO leadership. This organization works with governments and agencies throughout the world to promote universal use of iodized salt. Hopefully the alarming persistence of such an easily prevented calamity will be greatly reduced.
Submitted by Roger Boe, MD
GBGM Health Consultant