Iodine Defiency Disorders are the world's most prevalent cause of preventable mental retardation. Humans require about 1 teaspoon of iodine, taken in very small doses every day over an entire lifetime. Going without that iodine impairs the function of the thyroid gland, leading to hypothyroidism, in which the thyroid produces too little of its endocrine hormones. Since the thyroid hormones are responsible for human growth and development, hypothyroidism can lead to arrested development, cretinism, and mental retardation.
Large goiters can obstruct the trachea.
Donald Gordon, M.D., has written an HTML document on the Thyroid Gland including the Consequences of long-term iodine deficiency . Iodine deficiency disorders are most common in underdeveloped and poor areas of the world. An estimated 1.5 billion people are at risk in countries like China and India and some African countries. A lack of salt is not the only problem to solve. People in affected areas must also use iodized, rather than the cheaper noniodized salt.