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,
osteoporosis, and muscle wasting. The
hyperthyroidism is caused by autonomous nodular growth and function of the thyroid gland and it is accompanied by a high frequency of
goiter. Pregnant women and small children are not immediately endangered but the consequences of severe
iodine deficiency for brain development are grave and a considerable safety margin is advisable. Moreover, a shift toward less malignant types of
thyroid cancer and a lower radiation dose to the thyroid in case of nuclear fallout support that mild-to-moderate
iodine deficiency should be corrected. However, there is evidence that a high
iodine intake may be associated with more
autoimmune hypothyroidism, and that
Graves' disease may manifest at a younger age and be more difficult to treat. Hence, the
iodine intake should be brought to a level at which
iodine deficiency disorders are avoided but not higher.
Iodine supplementation programs should aim at relatively uniform
iodine intake, avoiding deficient or excessive
iodine intake in subpopulations. To adopt such a strategy, surveillance programs are needed.