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 par ameter to consider when evaluating iodine deficiency disorders in a populat ion. 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 Registratio n System in Denmark in age groups between 18 and 65 years were examined. Th yroid dysfunction was evaluated from blood samples and questionnaires, and compared with results from ultrasonography. Results: Median iodine excretion was 53 mu g/l in Aalborg and 68 mu g/l in Copenhagen. Previously diagnosed thyroid dysfunction was found with the sam e prevalence in the regions. Serum TSH was lower in Aalborg than in Copenha gen (P = 0.003) and declined with age in Aalborg, but not in Copenhagen. No t previously diagnosed hyperthyroidism was found with the same overall prev alence in the regions, but in age > 40 years hyperthyroidism was more preva lent in Aalborg (1.3 vs 0.5%, P = 0.017). Not previously diagnosed hypothyr oidism was found more frequently in Aalborg (0.6 vs 0.2%, P = 0.03). Hypert hyroidism was more often associated with macronodular thyroid structure at ultrasound in Aalborg and hypothyroidism was more often associated with pat chy thyroid structure in Copenhagen. Conclusions: Significant differences in thyroid dysfunction were found betw een the regions with a minor difference in iodine excretion. The findings a re in agreement with a higher prevalence of thyroid autonomy among the elde rly in the most iodine-deficient region.