The term Iodine Deficiency Disorders (IDD) refers to all the ill-effects of iodine deficiency in a population that can be prevented by insuring that the population has an adequate intake of iodine (1, 2). These effects are listed in Table 1. The presently recommended daily intake of iodine is shown in Table 2. The recommendation for pregnant and lactating women was recently increased up to 250μg/day by WHO (de Benoist and Delange, in press).
Table 1. The Spectrum of Iodine Deficiency Disorders, IDD.
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Adapted from Hetzel (1), Vanderpump et al. (52), Laurberg et al. ( 194) and Stanbury et al. (175). |
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Fetus |
Abortions Stillbirths Congenital anomalies Increased perinatal mortality Endemic cretinism |
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Neonate |
Neonatal goiter Neonatal hypothyroidism Endemic mental retardation Increased susceptibility of the thyroid gland to nuclear radiation |
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Child and adolescent |
Goiter (Subclinical) hypothyroidism Impaired mental function Retarded physical development Increased susceptibility of the thyroid gland to nuclear radiation |
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Adult |
Goiter with its complications Hypothyroidism Impaired mental function Spontaneous hyperthyroidism in the elderly Iodine-induced hyperthyroidism Increased susceptibility of the thyroid gland to nuclear radiation |
Table 2. Recommended daily intake of iodine
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From WHO/UNICEF/ICCIDD (2), WHO ( in press) |
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Iodine deficiency is now recognized as a global problem with large populations at risk who are living in an environment where the soil has been deprived of iodine. This arises from the distant past through glaciation, compounded by the leaching effects of snow, water and heavy rainfall, which removes iodine from the soil. The mountainous regions of Europe, the Northern Indian Subcontinent, the extensive mountain ranges of China, the Andean region in South America and the lesser ranges of Africa are all iodine deficient. But in addition we now know that the soil of flooded river valleys is also deprived of iodine as in the Ganges Valley in India, the Irawaddy Valley in Burma, and the Songkala valley in Northern China, which indicates that the problem of iodine deficiency is more widespread than previously suspected. The deficiency in the soil leads to iodine deficiency in all forms of plant life and cereal grown in the soil. Hence populations living in systems of subsistence agriculture are "locked into" iodine deficiency (3).
Brain damage and irreversible mental retardation are the most important disorders induced by iodine deficiency : in 1990 it has been estimated that among the 1572 million people in the world exposed to iodine deficiency (28.9 % of the world population), 11.2 million were affected by overt cretinism, the most extreme form of mental retardation due to the deficiency and that another 43 million people were affected by some degree of mental impairment (4). It therefore appeared that iodine deficiency was the leading cause of preventable mental retardation.
The present chapter will provide a global overview of the disorders induced by iodine deficiency. Special emphasis will be put on recent developments in the concept of IDD such as the role of iodine deficiency in the development of brain damage and mental retardation ; goiter seen as a sign of maladaptation to iodine deficiency rather than as the adaptative process to the deficiency ; assessment of the iodine status of a population ; and control of IDD including present achievements ; monitoring and side effects.
Extensive and recent global reviews of the different aspects of IDD are available elsewhere (5-9).