IODINE INTAKE AND THE PATTERN OF THYROID-DISORDERS - A COMPARATIVE EPIDEMIOLOGIC-STUDY OF THYROID ABNORMALITIES IN THE ELDERLY IN ICELAND AND IN JUTLAND, DENMARK

Thyroid abnormalities are common in all populations, but it is difficu lt to compare results of epidemiological studies, because different me thods have been used for evaluation. We studied the importance of the population iodine intake level for the prevalence rate of various thyr oid abnormalities in elderly subjects. Random samples of elderly subje cts (68 yr) were selected from the central person registers in Jutland , Denmark, with low (n = 423) and, in Iceland, with longstanding relat ively high (n = 100) iodine intake. Females from Jutland had a high pr evalence of goiter or previous goiter surgery (12.2%), compared with m ales from Jutland (3.2%) and females (1.9%) and males (2.2%) from Icel and. Abnormal thyroid function was very common in both areas, with ser um TSH outside the reference range in 13.5% of subjects from Jutland a nd 19% of those from Iceland. In Jutland, it was mainly thyroid hyperf unction (9.7% had low, 3.8% had high serum TSH), whereas in Iceland, i t was impaired thyroid function (1% had low, 18% had high serum TSH). All subjects with serum TSH more than 10 mU/L had autoantibodies in se rum, but antibodies were, in general, more common in Jutland than in I celand. Thus, thyroid abnormalities in populations with low iodine int ake and those with high iodine intake develop in opposite directions: goiter and thyroid hyperfunction when iodine intake is relatively low, and impaired thyroid function when iodine intake is relatively high. Probably, mild iodine deficiency partly protects against autoimmune th yroid disease. Thyroid autoantibodies may be markers of an autoimmune process in the thyroid or secondary to the development of goiter.