Thyroid disorders in mild iodine deficiency

Comparative epidemiologic studies in areas with low and high iodine intake and controlled studies of iodine supplementation have demonstrated that the major consequence of mild-to-moderate iodine deficiency for the health of the population is an extraordinarily high occurrence of hyperthyroidism in elderly subjects, especially women, with risk of cardiac arrhythmias, osteo porosis, and muscle wasting. The hyperthyroidism is caused by autonomous no dular growth and function of the thyroid gland and it is accompanied by a h igh frequency of goiter. Pregnant women and small children are not immediat ely endangered but the consequences of severe iodine deficiency for brain d evelopment are grave and a considerable safety margin is advisable. Moreove r, a shift toward less malignant types of thyroid cancer and a lower radiat ion dose to the thyroid in case of nuclear fallout support that mild-to-mod erate iodine deficiency should be corrected. However, there is evidence tha t a high iodine intake may be associated with more autoimmune hypothyroidis m, and that Graves' disease may manifest at a younger age and be more diffi cult to treat. Hence, the iodine intake should be brought to a level at whi ch iodine deficiency disorders are avoided but not higher. Iodine supplemen tation programs should aim at relatively uniform iodine intake, avoiding de ficient or excessive iodine intake in subpopulations. To adopt such a strat egy, surveillance programs are needed.