Correcting iodine deficiency disorders

Preventing and treating the causes of human ill-health arising from dietary deficiency of iodine.

The WHO estimated in 1990 that there were 1,000 million people at risk of Iodine Deficiency Disorder (IDD) in developing countries and 20 million suffering mental defect due to iodine deficiency. 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, including dwarfism and severe mental retardation. It is the most common cause of preventable mental defect in the world today.

Iodine sufficiency is defined as median UIC of 100-299 micrograms per liter in school-aged children and greater than or equal to 140 micrograms per liter in pregnant women.

Most people are at risk of iodine deficiency because they live in an iodine-deficient environment characterized by soil from which iodine has been leached by glaciation, high rainfall or flood. Such areas exist on all continents of the world. Currently the most "at risk" populations are in Indonesia, Papua New Guinea, Ecuador, Peru, Bolivia, Columbia, Argentina, India, Bangladesh, China, Bhutan, Nepal, Burma and Zaire. The problem manifests until there is dietary diversification (such as that which occurred in Europe late in the 19th century and in the early decades of the 20th century), or, alternatively, until some form of iodine supplement is given.

Iodized salt has been the major method for combatting iodine deficiency since the 1920s, when it was first successfully used in Switzerland. Since then successful programmes have been reported from a number of countries including Central and South America ([eg] Guatemala and Columbia), Finland, China, and Taiwan. In Asia, the cost of iodized salt production and distribution is of the order of 3-5 cents per person per year. However, the difficulties of production and maintenance of quality of iodized salt (which deteriorates if left uncovered or exposed to heat), and resistance to change in traditional dietary sources of salt, especially in Asia, have led to the adoption of universal salt iodation for India in 1992.

An alternative iodine supplement, successfully used in New Guinea, South America and Nepal, is iodized oil injections. Such treatment is effective for several years and is especially appropriate for isolated village communities and for concurrent administration with other injections as part of a mass programme. Iodized oil can also be given by mouth but is effective for periods of around 1 year.

The International Council for Control of Iodine Deficiency assists and promotes adaptive research, practical validation and transfer of technology of existing and emerging results of research and management investigations; advises on adaptive and practical training programmes; fosters cooperation in IDD control between developed and developing regions; and encourages coordination of IDD research, especially for benefit of developing countries. The Council cooperates with major international aid agencies, particularly WHO and UNICEF, and key bilateral aid-giving agencies, in the development of national iodine deficiency disorders (IDD) control programmes in countries with significant IDD problems. The UN agencies adopted a global strategy for prevention and control of IDD in 1986.

In the last five years, over 500 million people in twelve of the most seriously affected countries have begun using iodized salt. As a result, an estimates 120 million children have been spared the risk of physical and mental impairment. China plans to eliminate its iodine deficiency problem by the year 2000 by adding iodine to salt, and shutting down the black market in noniodized salt, which is cheaper and comprises one third of the Chinese salt market.

Mandatory salt iodization programs, to which 70% of the world's population are subject, have by and large eliminated iodine deficiency in most industrialized countries:  According to a 2013 study, 10 countries have iodine excess, 111 countries have sufficient iodine intake, 9 countries are moderately deficient, 21 are mildly deficient, and none are considered severely deficient, as defined by a median urinary iodine concentration of 100-299 μg/L in school-aged children (Pearce, E.N., Andersson, M., & Zimmermann, M.B. (2013). Global iodine nutrition: Where do we stand in 2013? Thyroid, 23(5), 524-528). For instance, after the development of the universal salt iodization initiative in China, median urinary iodine escalated from 164.8 μg/L in 1995 to 238.6 μg/L in 2011, well beyond the 100.0 to 199.0 μg/L levels recommended by the World Health Organization (WHO) from prevention of iodine deficiency disorders (IDD) (WHO/UNICEF/ICCIDD (2001). Assessment of the iodine deficiency disorders and monitoring their elimination: A Guide for Programme Managers. World Health Organization: Geneva). The most recent Food and Drug Administration's Total Diet Study also revealed that the U.S. population has adequate dietary iodine, with estimated average daily iodine intake ranging from 138 to 353 micrograms per person (Murray, C.W. et al. (2008). US Food and Drug Administration's Total Diet Study: dietary intake of perchlorate and iodine. Journal of Exposure Science and Environmental Epidemiology, 18, 571-580). Canada and Mexico are likewise iodine sufficient.

Of the many disabling conditions that come massively in the way of human development, the endemic deficiency in iodine is second to none, in the severity of its consequences coupled with the spread of its prevalence. In some areas of the world 4 to 15% of the newborn infants are condemned to the destruction of their mental and physical health.

Iodine is a narrow therapeutic index or "Goldilocks" nutrient, where too much and too little is problematic for the thyroid.  Although iodine prophylaxis programs may decrease goiter prevalence, epidemiological research in several iodine-replete countries suggest increased iodine intake correlates with an increased incidence of Hashimoto’s throiditis and positive thyroid autoantibodies.