Iodine deficiency causes goitre, hypothyroidism, retarded physical development and impaired mental function, increased rate of spontaneous abortion and stillbirth, neurological cretinism, including deaf mutism and myxoedematous cretinism, dwarfism and severe mental retardation. It is the most common cause of preventable mental defect in the world today.
WHO estimated in 1990 that there were one billion people at risk of iodine deficiency disorders in developing countries. 190 million suffered from goitre and 20 million from mental defects due to iodine deficiency. Of these, more than 3 million were overt cretins. In 1997, 60% of the world's edible salt was iodized to combat the deficiency.
A 1995 survey of infants in China revealed that 35% to 65% had iodine deficiencies. A third of the global 1.6 billion iodine deficiency cases are in China. In 1997 in Georgia there was a widespread iodine deficiency and the 50,000 babies born there will be intellectually duller than normal by 10 IQ points.