The benefits of adequate iodine intake.

In past decades, researchers in various countries have studied the consequences of iodine deficiency on the mental and physical development of children and adults. Iodine deficiency proved to have disastrous consequences on cognitive and psychomotor development for a limited group (i.e., DeLong 1989). These are the so-called cretins, who make up more than 10% of the population in some areas. The World Health Organization estimates the worldwide number of overt cretins at around 5.7 million (Hetzell994). Outcomes of study of the effects of iodine deficiency on the development of the noncretinous portion of a population living in an iodine-deficient area are less clear cut. While some studies pointed to a strong negative effect, little or no effect was found in others. To obtain an overall picture of the current state of knowledge, the first part of this paper summarizes the results of a great many studies that have been performed in recent years. All these studies involved a comparison of the mental and psychomotor development in two groups of children and/or adults: (1) a non-iodine-deficient group people living in a non-iodine-deficient area or children whose mothers were injected with iodized oil in the first part of their pregnancy; and (2) an iodine-deficient group -people living in an area with a serious iodine deficiency. Meta-analysis was used to combine the results of the studies. In the second part of this paper, the outcomes are discussed of a recent study of the effect of iodine supplementation on the mental and psychomotor development of children born and raised in an iodine-deficient area in Malawi (Shrestha 1994). Although very little research has been done in this field, it is of great importance to know whether the negative effects of iodine shortage can be corrected at a later age through iodine supplementation.