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

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

J Clin Endocrinol Metab. 2018 Dec 14;:

Authors: Petersen M, Knudsen N, Carlé A, Andersen S, Jørgensen T, Perrild H, Ovesen L, Rasmussen LB, Thuesen BH, Pedersen IB

Abstract
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.

PMID: 30551165 [PubMed - as supplied by publisher]

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