Iodine Intake In Population Research Articles

Iodine intake and the pattern of thyroid disorders: a comparative epidemiological study of thyroid abnormalities in the elderly in Iceland and in Jutland, Denmark.

Thyroid abnormalities are common in all populations, but it is difficult to compare results of epidemiological studies, because different methods have been used for evaluation. We studied the importance of the population iodine intake level for the prevalence rate of various thyroid abnormalities in elderly subjects. Random samples of elderly subjects (68 yr) were selected from the central person registers in Jutland, Denmark, with low (n = 423) and, in Iceland, with longstanding relatively high (n = 100) iodine intake. Females from Jutland had a high prevalence of goiter or previous goiter surgery (12.2%), compared with males from Jutland (3.2%) and females (1.9%) and males (2.2%) from Iceland. Abnormal thyroid function was very common in both areas, with serum TSH outside the reference range in 13.5% of subjects from Jutland and 19% of those from Iceland. In Jutland, it was mainly thyroid hyperfunction (9.7% had low, 3.8% had high serum TSH), whereas in Iceland, it 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 serum, but antibodies were, in general, more common in Jutland than in Iceland. Thus, thyroid abnormalities in populations with low iodine intake 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 thyroid disease. Thyroid autoantibodies may be markers of an autoimmune process in the thyroid or secondary to the development of goiter.

High incidence of multinodular toxic goitre in the elderly population in a low iodine intake area vs. high incidence of Graves' disease in the young in a high iodine intake area: comparative surveys of thyrotoxicosis epidemiology in East‐Jutland Denmark and Iceland

Little is known about the optimum level of iodine intake for iodine supplementation programmes, or about the effects of the high levels of iodine intake that are found in some countries. We compared the incidence of different types of hyperthyroidism in East-Jutland Denmark with a low average iodine intake but no endemic goitre, and the incidence in Iceland with a relatively high iodine intake. Hyperthyroidism was more common in East-Jutland than in Iceland, due to a much higher incidence of multinodular toxic goitre and also of single toxic adenoma. Most of the patients with these diseases were over 50 years of age. By contrast, the incidence of Graves' disease was significantly higher in Iceland than in East-Jutland. This difference was most marked in the younger age groups, in which hyperthyroidism was more than twice as common in Iceland as in East-Jutland. These results demonstrate that even mild iodine deficiency has a significant effect on population health, since it leads to a high incidence of autonomous thyroid nodules with hyperthyroidism in the elderly population. However, population iodine intake probably should not exceed a level much higher than that necessary to avoid iodine deficiency, otherwise Graves' disease may be induced in the young population.