Iodine and neuropsychological development.

The establishment of the essential link among iodine deficiency, thyroid function and brain development has emerged from a fascinating combination of clinical, epidemiologic and experimental studies. The central human phenomenon that focuses this relationship is the condition of endemic cretinism, described from the Middle Ages and characterized in its fully developed form by severe brain damage, deaf mutism and a spastic state of the hands and feet. The demonstration of the prevention of cretinism in a double-blind controlled trial with injections of iodized oil in Papua New Guinea (1966-1970) established the causal role of iodine deficiency in cretinism by an effect on the developing fetal brain. Cretinism could not be prevented unless the iodized oil was given before pregnancy. Iodine deficiency is now regarded by the WHO as the most common preventable cause of brain damage in the world today, with at least 30 million suffering from this preventable condition. Since 1986 the international NGO, the International Council for Control of Iodine Deficiency Disorders, has worked closely as an expert group with WHO and UNICEF in assisting countries with a program of universal salt iodization for the elimination of iodine deficiency as a cause of brain damage by the year 2000. In 1996, WHO reported that 56% of the population of 83 developing countries now had adequate access to iodized salt. This represents an increase of 750 million since 1990 with protection of 12 million children.