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The Capital Region of Denmark - a part of Copenhagen University Hospital
E-pub ahead of print

Increased incidence rate of hypothyroidism after iodine fortification in Denmark. A 20 year prospective population-based study

Research output: Contribution to journalJournal articleResearchpeer-review

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Objective: To monitor the impact of a cautious iodine fortification (IF) on the incidence of overt hypothyroidism in two sub-populations with different levels of preexisting iodine deficiency (ID).

Design: A 20 years (1997-2016) prospective population-based study identified all new cases of diagnosed overt biochemical hypothyroidism in two open cohorts: a Western cohort with moderate ID (n=309,434, January 1st, 1997) and an Eastern cohort with mild ID (n=224,535, January 1st, 1997). A diagnostic algorithm was applied to all thyroid function tests performed within the study areas and possible new cases were verified individually. Mandatory IF of salt was initiated in mid-2000 (13 p.p.m.). The present study is a part of the DanThyr study.

Results: At baseline, standardized incidence rate (SIR) of hypothyroidism was 32.9 and 47.3/100.000/year in the cohort with moderate and mild ID, respectively. The SIR of hypothyroidism increased significantly in both cohorts after implementing mandatory IF with peak values of 150 % in 2014-16 for the moderate ID cohort and 130 % in 2004-05 for the mild ID cohort. Significant increases in SIR were seen among the young and middle aged of both cohorts, whereas no changes were seen among the elderly (60+ y). The follow-up period for the mildly iodine deficient cohort was restricted up to and including 2008.

Conclusion: The cautious initiation of the IF program in Denmark caused a sustained increase in hypothyroidism incidence among subjects residing areas of moderate and mild iodine deficiency, but only among the young and middle aged.

Original languageEnglish
JournalThe Journal of clinical endocrinology and metabolism
ISSN0021-972X
DOIs
Publication statusE-pub ahead of print - 14 Dec 2018

ID: 55837455