Iodine deficiency: an ancient problem in a modern world.

Iodine has long been known as an essential element for humans, and for mammals in general, where it is concentrated in the thyroid gland, being a vital component of the thyroid hormone thyroxine. Deprivation of iodine results in a series of iodine deficiency disorders (IDD), the most commonly recognized 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 that causes stunted growth and general development, together with brain damage. However, although these 2 diseases are easily recognizable, the more insidious problem is that iodine deficiency impairs brain development in children, even when there is no obvious physical effect; indeed, it has been suggested that iodine deficiency is the most common preventable cause of mental retardation. Endemic goiter and cretinism, together with related IDD, have long been recognized as serious health problems, and, consequently, much work has been carried out on the etiology and geographical distribution of these diseases. Although it has been suggested that other elements and factors may be involved, it is generally agreed that the primary cause of IDD is a lack of iodine in the diet. Endemic goiter appears to have been identified by the ancient Chinese, one Chinese medical writer from the 4th century AD noted the use of the brown seaweeds Sargassum and Laminaria (which are now known to be very iodine rich) for its treatment (1). However, there are many earlier records in ancient literature of seaweeds and burnt sea sponges being used in the treatment of endemic goiter possibly from as early as 2700 BC (1). Iodine was discovered by the French chemist Bernard Courtois in 1811 when he accidentally added concentrated sulfuric acid to the seaweed Fucus vesiculosus, one of the seaweeds used in goiter treatment. It was soon realized that iodine was the active ingredient in the treatment, being identified as an essential element in human nutrition, consequently, thyroxine was discovered and identified in 1919. Despite this early recognition of the role of iodine in endemic goiter and related disorders, it is apparent that IDD is still affecting large numbers of people worldwide, with some estimates suggesting that around 2 thousand million of the world’s population are at risk. Before the middle of the 20th century iodine deficiency problems affected virtually every country (2). Subsequent to the addition of iodine to the diet as a prophylactic, mainly through iodized salt, IDD had more or less been eradicated from the developed world by the 1970s and were generally regarded as diseases of the poor. Although a large percentage of those currently at risk of IDD are located in the developing world, over the last 15 years or so it has reemerged in some of the more affluent countries of Western Europe, such as Austria, Belgium, Demark, Germany, and France, and is also re-emerging in other countries, e.g., Australia. Based on the data of Dunn and van der Haar (3), Figure 1 indicates the general global distribution of IDD. IODINE GEOCHEMISTRY