Environmental Iodine in Iodine Deficiency Disorders, with a Sri Lankan Example

Abstract

Iodine is an essential element for human and other animal health and forms an important constituent of the thyroid hormones thyroxine (T4, also known as tetraiodothyronine) and triiodothyronine (T3). These hormones play a fundamental biological role in controlling growth and development (Hetzel and Maberly 1986). If the amount of utilizable iodine reaching the thyroid gland is inadequate, or if thyroid function is impaired, hormone production can be reduced, resulting in a group of conditions collectively referred to as Iodine Deficiency Disorders (IDD) (Fernando et al. 1987, Hetzel 1989). The World Health Organization (WHO 1993) estimate that in excess of one billion people worldwide are at risk from IDD, the most common manifestation of which is goiter (Fig. 9.1). Iodine deficiency is the world’s most common cause of preventable mental retardation and brain damage, and has a significant negative impact on the social and economic development of communities. Although it is likely that IDD are multifactorial diseases involving other trace element deficiencies and goitrogens (goiter-promoting substances) in foodstuffs, a lack of adequate dietary iodine remains a major concern (Stewart and Pharaoh 1996). The link between environmental iodine and IDD has been known for the last 80 years. During this time, the medical community has become well organized when tackling the problem, exemplified by the work of the International Council for the Control of IDD (ICCIDD) ( <http:// www.tulane.edu/~icec/icciddhome.htm>), which provides an excellent dissemination point for discussion and information. Remediation strategies often focus on enhancing dietary intakes of iodine via the introduction of iodinated salt and iodinated oil programs (Stanbury and Hetzel 1980). However, these methods are not always successful and other strategies, including environmental interventions, require development (DeLong et al. 1997) In contrast to the wealth of information about the symptoms, assessment, and treatment of IDD, there is very little on the primary cause, a lack of readily available iodine in the environment and diet. Our knowledge of environmental iodine geochemistry is limited, mainly because the analytical methods for assessment are not routine and iodine is not an element that has been systematically determined in geochemical surveys. However, in the past two decades, improved analytical methodologies and an interest in iodine from different perspectives have added much to our knowledge.