Comparative study of thyroid function and types of thyroid dysfunction in two areas in Denmark with slightly different iodine status.

OBJECTIVE The pattern of thyroid dysfunction seems to depend on the iodine status of the population. Prevalence of thyroid dysfunction could be a parameter to consider when evaluating iodine deficiency disorders in a population. DESIGN Comparative cross-sectional investigation in two regions in Denmark with marginally different iodine excretion. METHODS A random selection of 4649 participants from the Civil Registration System in Denmark in age groups between 18 and 65 years were examined. Thyroid dysfunction was evaluated from blood samples and questionnaires, and compared with results from ultrasonography. RESULTS Median iodine excretion was 53 microg/l in Aalborg and 68 microg/l in Copenhagen. Previously diagnosed thyroid dysfunction was found with the same prevalence in the regions. Serum TSH was lower in Aalborg than in Copenhagen (P=0. 003) and declined with age in Aalborg, but not in Copenhagen. Not previously diagnosed hyperthyroidism was found with the same overall prevalence in the regions, but in age >40 years hyperthyroidism was more prevalent in Aalborg (1.3 vs 0.5%, P=0.017). Not previously diagnosed hypothyroidism was found more frequently in Aalborg (0.6 vs 0.2%, P=0.03). Hyperthyroidism was more often associated with macronodular thyroid structure at ultrasound in Aalborg and hypothyroidism was more often associated with patchy thyroid structure in Copenhagen. CONCLUSIONS Significant differences in thyroid dysfunction were found between the regions with a minor difference in iodine excretion. The findings are in agreement with a higher prevalence of thyroid autonomy among the elderly in the most iodine-deficient region.