Dr. Robert Volpé, MD, FRCP(C), FACP, FRCP (Edin. & London)
Endocrinologist, The Wellesley Central Hospital Site, St. Michael's Hospital, Toronto, Professor Emiritus, University of Toronto
Medical Advisor Thyroid Foundation of Canada
Dr. Volpé delivered this address to the Kiwanis Club of Kingston on Monday October 5, 1998. Kiwanis International is raising 75 million dollars by the year 2000 to help eradicate Iodine Deficiency Disorders
Iodine is found in the earth's crust in sparse amounts and is in the form of iodide. Since iodide is soluble, soils will be lowest in iodine in areas where there is much rainfall or where glaciers have melted and leached the iodine out of the soil.
The most important iodine deficient areas in the world include the Himalayas and the Andes, but our own soil in the great Lakes Basin is also iodine deficient. However, in Canada we have iodized the salt and thus have completely rid our population of iodine deficiency.
Based on the most recent evaluation, iodine deficiency currently represents a significant public health problem for 1575 million people (almost 30% of the world's population) in 110 countries. 655 million are affected by goitre, 20 million are believed to be significantly mentally handicapped as a result of iodine deficiency which is therefore the most prevalent preventable cause of impaired intellectual development in the world today.
Although the disorders that result from iodine deficiency are preventable by appropriate iodine supplementation, they continue to occur because of various socio-economic, cultural and political limitations to adequate iodine supplementation programmes.
Severe iodine deficiency may manifest itself by Cretinism i.e. children born with severe hypothyroidism. Neonates and young infants constitute the target population for the effects of iodine deficiency because, from a public health viewpoint, the most important complications of iodine deficiency are irreversible brain damage and mental retardation which result from iodine deficiency and thyroid failure during fetal and early postnatal life.
Other naturally occurring goitrogens can aggravate or simulate iodine deficiency, and these include such foods as cassava, maize, bamboo shoots, sweet potatoes, lima beans, and the Brassica group of vegetables. Iodine deficiency and/or these goitrogens interfere with the production of thyroid hormone, thus causing an increase in TSH, an increased size of the thyroid gland (goitre), and hypothyroidism.
The consequences of iodine deficiency even in developed areas such as Europe is enormous. For example the cost of the diagnosis and treatment of goitre due to iodine deficiency in Germany in 1986 was estimated at 700 million dollars, yet prevention by iodized salt would cost only 2-8 cents per person per year.
Elevated thyroid uptake due to iodine deficiency aggravates the risk of thyroid irradiation and development of thyroid cancer in the case of a nuclear accident. Even in Europe, clinically euthyroid school children born and living in an iodine deficient environment exhibit subtle or even overt neuropsychointellectual deficits as compared to controls living in the same ethnic, demographic, nutritional and socio-economic system, except that they are not exposed to iodine deficiency.
Treatment and prophylaxis of iodine deficiency disorders
Prolonged administration of iodide or of thyroid hormone has been found highly effective in reducing the size of endemic goitre. Surgical treatment is often justified in large goitres with pressure symptoms.
Nevertheless, such types of treatment are, in practice, impossible to apply to a general population in view of the epidemiologic size of the problem and the general lack of adequate medical infrastructure in the most severely affected population. The most logical approach is the introduction of iodine prophylaxis.
For almost eighty years, iodized salt has been used as the simplest and most effective way of providing extra iodine in the diet. Iodine is most often added in the form of potassium iodide, but iodate is preferred in humid regions owing to its greater stability. Many countries have long since introduced iodized salt which resulted not only in a dramatic reduction in the prevalence of goitre but also progressive disappearance of endemic Cretinism. In the United States and Canada, one part of iodide is added to 10,000 parts of salt. In other countries, the ratio is one to 100,000. Iodination of water has been successfully used in some areas with adequate water supply and control of the iodination process. Iodination of irrigation water has been successfully used in China.
However, in many developing countries with severe problems of endemic goitre, iodination of salt, bread or water has failed to prevent or eradicate the disease because various socio- economic, climatic or geographic conditions make systemic iodine supplementation difficult or even impossible, such as when iodized salt did not reach the endemic areas or when house salt was not available.
In such conditions, prophylaxis and therapy can be achieved extremely effectively by injecting slowly resorbable iodized oil given by intramuscular injection or orally.
It appears necessary to inject the entire population from birth to 45 years of age for females and from birth to 20 years of age for males. This is, of course, a very large logistic problem and this problem has not been entirely overcome.
The principal complication of iodine prophylaxis is the occurrence of thyrotoxicosis (hyperthyroidism). However, this is exceptional and does not negate the enormous benefit that follows the introduction of iodide prophylaxis in endemic goitre regions. .
