Environmental iodine intake affects the type of nonmalignant thyroid disease

The relationship between the iodine intake level of a population and the oc currence of thyroid diseases is U-shaped with an increase in risk from both low and high iodine intakes. Developmental brain disorders and endemic goi ter caused by severe iodine deficiency may seriously deteriorate overall he alth status and economic performance of a population. Severe iodine deficie ncy with a median 24-hour urinary iodine excretion of the population below 25 mug needs immediate attention and correction. Less severe iodine deficie ncy with median urinary iodine excretion below 120 mug per 24 hours is asso ciated with multinodular autonomous growth and function of the thyroid glan d leading to goiter and hyperthyroidism in middle aged and elderly subjects . The lower the iodine intake, the earlier and more prominent are the abnor malities. At the other end of the spectrum, severely excessive iodine intak e starting at median urinary iodine excretion levels around 800 mug per 24 hours is associated with a higher prevalence of thyroid hypofunction and go iter in children. A number of studies indicate that moderate and mild iodin e excess (median urinary iodine > 220 mug per 24 hours) are associated with a more frequent occurrence of hypothyroidism, especially in elderly subjec ts. The exact mechanism leading to this has not been clarified, and more st udies are needed to define the limits of excessive iodine intake precisely. Due to the frequent occurrence of thyroid disorders, proper monitoring and control of the population iodine intake level is a cost-effective alternat ive to diagnosing, therapy and control of the many individual cases of thyr oid diseases that might have been prevented.