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Increased Incidence Rate of Hypothyroidism After Iodine Fortification in Denmark: A 20-Year Prospective Population-Based Study

2018; Oxford University Press; Volume: 104; Issue: 5 Linguagem: Inglês

10.1210/jc.2018-01993

1945-7197

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

Vitamin D Research Studies

Objective: To monitor the impact of a cautious iodine fortification (IF) on the incidence of overt hypothyroidism in two subpopulations with different levels of preexisting iodine deficiency (ID).Design: A 20-year (1997 to 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; 1 January 1997) and an eastern cohort with mild ID (n = 224,535; 1 January 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 ppm).The current study is a part of the DanThyr study.Results: At baseline, standardized incidence rates (SIRs) of hypothyroidism were 32.9 and 47.3/ 100.000/y in the cohorts 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 to 2016 for the moderate ID cohort and 130% in 2004 to 2005 for the mild ID cohort.Significant increases in SIR were seen among the young and middle-aged participants of both cohorts, whereas no changes were seen among the elderly participants ($60 years).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 in areas of moderate and mild ID but only among the young and middle-aged participants.(J Clin Endocrinol Metab 104: 1833-1840, 2019) I ron deficiency (ID) is one of the most common types of specific nutritional deficiencies globally.Endemic goiter is common in severe iron-deficient areas.Endemic cretinism with mental retardation may also result from severe ID (1).Moderate and mild ID is associated with a high prevalence of toxic and nontoxic multinodular goiter (1, 2).According to World Health Organization recommendations, daily iodine intake for men, nonpregnant women, and children above 12 years of age should be