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

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Mads Petersen, Nils Knudsen, Allan Carlé, Stig Andersen, Torben Jorgensen, Hans Perrild, 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