17. Soils and Iodine Deficiency

Iodine has long been known as an essential element for humans, and mammals in general, where it is concentrated in the thyroid gland. It is a component of the thyroid hormone thyroxine. Deprivation of iodine results in a series of iodine deficiency disorders (IDD), the most obvious of which is endemic goiter, a condition where the thyroid gland becomes enlarged in an attempt to be more efficient. Iodine deficiency during fetal development and in the first year of life can result in endemic cretinism, a disease which causes stunted growth and general development along with brain damage. However, while these two diseases are easily recognizable, perhaps the more insidious problem is that iodine deficiency impairs brain development in children even when there is no obvious physical effect. Many researchers have suggested that a relatively low degree of iodine deficiency during fetal development can result in a significant reduction of IQ in children. Indeed it has been suggested that iodine deficiency is the most common preventable cause of mental retardation (see Chaps. 8 and 9, this volume). For a detailed discussion of the problems resulting from iodine deficiency in humans the reader is referred to the many publications on the topic by Basil Hetzel (e.g. Hetzel 1987, 2001; Hetzel et al. 1990)