More hypothyroidism and less hyperthyroidism with sufficient iodine nutrition compared to mild iodine deficiency--a comparative population-based study of older people

Abstract

Objective: To assess the occurrence of thyroid disorders and autoimmunity in a geriatric population with long-standing recommended iodine intake of natural origin compared to mild iodine deficiency.

Design and setting: Cross-sectional, comparative, population-based study in two areas with different iodine intakes due to different tap water iodine contents.

Participants: Residents of Randers (n=212) or Skagen (n=218), Denmark, aged 75-80 years.

Measures: Blood samples were collected for measuring thyrotropin (TSH), triiodothyronine, thyroxine, thyroid peroxidase antibody (TPOAb), thyroglobulin antibody (TGAb), thyroglobulin (TG); iodine excretion estimated from iodine and creatinine measured in spot urine samples; questionnaire on history of thyroid disease, medication and vitamin use; clinical examination of the neck.

Results: Median urinary iodine excretion was 50 microg/24h in Randers and 177 microg/24h in Skagen (p<0.001). A history of thyroid disease was reported by 40 (9.3%) dominated by goitre (n=22) in Randers and hypothyroidism and Graves Disease (n=15) in Skagen (p<0.001). We found visible goitre in 26% of Randers dwellers and none in Skagen (p<0.001). Hyperthyroidism with TSH below the reference range was present in 26% of Randers and 6% of Skagen dwellers while 6% and 13%, respectively, were hypothyroid with TSH above the reference range (p<0.001). More Randers than Skagen participants harboured a thyroid antibody (42% vs. 32%, p=0.006).

Conclusions: Recommended iodine intake associated with more hypothyroidism, less hyperthyroidism and goiters, low TGAb prevalence and lower TG level in serum than did iodine deficiency. TPOAb was similar in the iodine replete and deficient geriatric populations.