What is IDD?
When the earth was formed, iodine was present in both land and water. Unfortunately, over the eons since the earth’s formation, much of the available iodine was washed out of the soil, especially in mountainous areas through the action of glaciers, and in flood plains by regular flooding. 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.
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. Thyroid hormones have many functions in the body, all of which are essential for normal physical and mental development, including growth. 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 goitre, which is the outward sign of iodine deficiency.
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. 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.
It is therefore obvious that iodine is 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. Iodine deficiency can cause abortion, stillbirth, 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. Table 1 shows the different disorders associated with iodine deficiency at different life stages. 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. 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.
What is a goitre?
A goitre (or goiter) ( Latin struma ) is a swelling in the neck (just below adam’s apple or larynx) due to an enlarged thyroid gland. The most common cause for goitre in the world is iodine deficiency.
Other causes are:
• Hashimoto’s thyroiditis
• Graves-Basedow disease
• juvenile goitre
• neoplasm of the thyroid
• thyroiditis (acute, chronic)
• side-effects of pharmacological therapy
Iodine is necessary for the synthesis of the thyroid hormones, triiodothyronine and thyroxine (T3 and T4). When iodine is not available these hormones cannot be made. In response to low thyroid hormones, the pituitary gland releases thyroid stimulating hormone (TSH).
Thyroid stimulating hormone acts to try and increase synthesis of T3 and T4, but also causes the thyroid gland to grow in size as a type of compensation. It is more common among women. Treatment may not be necessary if the goitre is not caused by disease and is small. Removal of the goitre may be necessary if it is causing difficulty with breathing or swallowing.
Goitre was previously common in many areas that were deficient in iodine in the soil. The condition now is practically absent in affluent nations, where table salt is fortified with iodine.
There are fears by some health workers that a resurgence of goitre might occur because of the trend to use rock salt and/or sea salt (which has not been fortified with iodine) and also less salt use in general.