Iodine deficiency influences thyroid autoimmunity in old age--a comparative population-based study

Objective

To assess thyroid autoimmunity among elderly people living in an area with low iodine intake compared to the sustained recommended iodine intake from a natural source, and to estimate the importance of migration.

Design and setting

Iodine content of drinking water is highly different in the Danish towns Randers and Skagen. We collected blood and spot urine samples from 430 long-term Randers and Skagen dwellers aged 75–80 years, who filled in a questionnaire. We measured thyroid peroxidase antibody (TPOAb) and thyroglobulin antibody (TGAb) in serum and iodine and creatinine in urine.

Results

Participation rate was 47% (n = 212 (men/women 82/130) in Randers; 218 (84/134) in Skagen). Iodine deficiency prevailed in Randers while Skagen dwellers were iodine replete (median urinary iodine 74 μg/24 h vs. 184 μg/24 h, p < 0.001). Thyroid antibodies were more frequent in Randers than in Skagen residents (42% vs. 32%; p = 0.006) and more likely with iodine excretion <50 μg/24 h (OR, 95%CI: 1.9, 1.1–3.4). Differences between towns increased with longer duration of residence as trends in the occurrence of TGAb and TPOAb were opposite (p < 0.001; p = 0.007).

Conclusions

Thyroid autoantibodies were common in old age, influenced by the iodine intake level, and the lowest frequency was found at the recommended iodine intake level.