Changes in subtypes of overt thyrotoxicosis and hypothyroidism following iodine fortification

Mads Petersen, Inge Bülow Pedersen, Nils Knudsen, Stig Andersen, Torben Jørgensen, Hans Perrild, Lars Ovesen, Lone Banke Rasmussen, Betina H Thuesen, Allan Carlé

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Objective: To investigate the impact of mandatory iodine fortification (IF) on the incidence of nosological subtypes of overt thyrotoxicosis and hypothyroidism. Design: We identified and scrutinized all possible new cases of overt thyrotoxicosis and hypothyroidism in an open cohort in Northern Jutland (n = 309 434; 1 January 1997) during the years 2014-2016. Individual medical history was evaluated to verify and detail the incidence of overt thyroid dysfunction and for classification into nosological subtypes. A number of cases were excluded during final verification due to spontaneous normalization of thyroid function, as they had no medical history suggesting a known condition, which could transiently affect thyroid function (subacute/silent thyroiditis, PPTD and iatrogenic thyroid dysfunction). An identical survey was conducted in 1997-2000 prior to mandatory IF of salt (13 µg/g) that was in effect from year 2001. Results: The standardized incidence rate (SIR) of verified overt thyrotoxicosis decreased markedly from 97.5/100 000/year in 1997-2000 to 48.8 in 2014-2016 (SIRR: 0.50 [95% CI: 0.45-0.56]). This was due to a distinct decrease in the SIR of multinodular toxic goitre (SIRR: 0.18 [0.15-0.23]), solitary toxic adenoma (SIRR: 0.26 [0.16-0.43]) and to a lesser degree Graves’ disease (SIRR: 0.67 [0.56-0.79]). SIR for overt hypothyroidism was unaltered by 2014-2016 (SIRR: 1.03 [0.87-1.22]). However, age distribution shifted with more young and fewer elderly cases of verified overt hypothyroidism. Conclusion: Mandatory IF caused a substantial reduction in SIR of verified overt thyrotoxicosis (especially of nodular origin) while avoiding an increase in SIR of verified overt hypothyroidism.

Original languageEnglish
JournalClinical Endocrinology
Issue number5
Pages (from-to)652-659
Number of pages8
Publication statusPublished - Nov 2019

Bibliographical note

© 2019 John Wiley & Sons Ltd.


  • epidemiology
  • hyperthyroidism
  • hypothyroidism
  • incidence
  • iodine
  • myxoedema
  • thyrotoxicosis


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