Thyrotoxicosis after iodine fortification: A 21-year Danish population-based study

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  • Mads Petersen
  • Knudsen, Nils Jakob
  • Allan Carlé
  • Stig Andersen
  • Torben Jorgensen
  • Perrild, Hans
  • Lars Ovesen
  • Lone Banke Rasmussen
  • Betina Heinsbaek Thuesen
  • Inge Bulow Pedersen
Monitoring the influence of cautious iodine fortification (IF) on the incidence rate of overt thyrotoxicosis in Denmark with formerly frequent multinodular toxic goitre.

A 21‐year (1997‐2017) prospective population‐based study identified all new cases of overt biochemical thyrotoxicosis in two open cohorts: a Western cohort with moderate iodine deficiency (ID) and an Eastern cohort with mild ID (total n = 533 969 by 1 January 1997). A diagnostic algorithm was applied to all thyroid function tests performed within the study areas. Mandatory IF of salt was initiated in mid‐2000 (13 ppm). This study is a part of DanThyr.

The standardized incidence rate (SIR) of thyrotoxicosis at baseline (1997‐1998) was 128.5/100.000/year in the cohort with moderate ID and 80.1 in the cohort with mild ID. SIR increased markedly in both cohorts during the initial years of IF (moderate/mild ID: +39/+52% in 2000‐2001/2004‐2005) and subsequently decreased to baseline level (mild ID) or below (moderate ID) by 2008. The decline was due to a marked decrease in the incidence rate among elderly subjects and a moderate decrease among the middle aged. The follow‐up period for the mildly iodine deficient cohort was restricted to 2008. A continuous decline in SIR was observed for the remainder of the study period in the area with moderate ID (33% below baseline in 2016‐2017).

The rise in thyrotoxicosis incidence with cautious mandatory IF returned to baseline level after 7‐8 years and levelled out at 33% below baseline in the population with previously moderate ID after 16‐17 years.
Original languageEnglish
JournalClinical Endocrinology
Issue number3
Pages (from-to)360-366
Number of pages7
Publication statusPublished - 2018

    Research areas

  • epidemiology, hyperthyroidism, incidence, iodine, thyrotoxicosis

ID: 210061718