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Lena Bjergved, Torben Jørgensen, Hans Perrild, Allan Carlé, Charlotte Cerqueira, Anne Krejbjerg, Peter Laurberg, Lars Ovesen, Inge Bülow Pedersen, Rasmussen Lone Banke, Nils Knudsen, Predictors of Change in Serum TSH after Iodine Fortification: An 11-Year Follow-Up to the DanThyr Study, The Journal of Clinical Endocrinology & Metabolism, Volume 97, Issue 11, 1 November 2012, Pages 4022–4029, https://doi.org/10.1210/jc.2012-2508
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Few data are available on the effect of iodine fortification on thyroid function development in a population.
Our objective was to evaluate changes in thyroid function after iodine fortification in a population and to identify predictors for changes in serum TSH.
A longitudinal population-based study of the DanThyr C1 cohort examined at baseline (1997–1998) and reexamined 11 yr later (2008–2010). The mandatory program for iodization of salt was initiated in 2000.
A total of 2203 individuals, with no previous thyroid disease, living in two areas with different levels of iodine intake, with measurement of TSH and participation in follow-up examination were included in the analysis.
Change in serum TSH was evaluated.
During the 11-yr follow-up, mean TSH increased significantly from 1.27 mU/liter [95% confidence interval (CI) = 1.23–1.30] to 1.38 mU/liter (CI = 1.34–1.43) (P < 0.001). The most pronounced increase was observed in the area with the highest iodine intake [1.30 mU/liter (CI = 1.25–1.35) to 1.49 mU/liter (CI = 1.43–1.55), P < 0.001], whereas the increase was not significant in the low-iodine-intake area [1.24 (CI = 1.19–1.29) to 1.28 (CI = 1.23–1.34), P = 0.06)]. Change in TSH was positively associated with the presence of thyroid peroxidase antibody at baseline (P < 0.001) and negatively associated with baseline thyroid enlargement (P < 0.001) and multiple nodules (P < 0.001).
Even small differences in the level of iodine intake between otherwise comparable populations are associated with considerable differences in TSH change at the 11-yr follow-up. Multinodular goiter predicted a less pronounced TSH increase during follow-up, which may be explained by iodine-dependent activity of autonomous nodules.