title: Predictors of change in serum TSH after iodine fortification: an 11-year follow-up to the DanThyr study.
abstract: BACKGROUND
  Few data are available on the effect of iodine fortification on thyroid function development in a population.
  
  
  OBJECTIVE
  Our objective was to evaluate changes in thyroid function after iodine fortification in a population and to identify predictors for changes in serum TSH.
  
  
  METHODS
  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.
  
  
  METHODS
  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.
  
  
  METHODS
  Change in serum TSH was evaluated.
  
  
  RESULTS
  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).
  
  
  CONCLUSIONS
  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.
authors.affiliation: Department of Endocrinology and Gastroenterology, Bispebjerg University Hospital, Bispebjerg Bakke 23, 2400 Copenhagen NV, Denmark. lena.baudler.bjergved@regionh.dk
authors.forename: Lena
authors.initials: L
authors.lastname: Bjergved
authors.forename: Torben
authors.initials: T
authors.lastname: Jørgensen
authors.forename: Hans
authors.initials: H
authors.lastname: Perrild
authors.forename: Allan
authors.initials: A
authors.lastname: Carlé
authors.forename: Charlotte
authors.initials: C
authors.lastname: Cerqueira
authors.forename: Anne
authors.initials: A
authors.lastname: Krejbjerg
authors.forename: Peter
authors.initials: P
authors.lastname: Laurberg
authors.forename: Lars
authors.initials: L
authors.lastname: Ovesen
authors.forename: Inge
authors.initials: I
authors.lastname: Bülow Pedersen
authors.forename: Rasmussen Lone
authors.initials: RL
authors.lastname: Banke
authors.forename: Nils
authors.initials: N
authors.lastname: Knudsen
mesh_terms: D000328:Adult; D000368:Aged; D003718:Denmark; D005260:Female; D005500:Follow-Up Studies; D005527:Food, Fortified; D006801:Humans; D007455:Iodine; D008137:Longitudinal Studies; D008297:Male; D008875:Middle Aged; D013972:Thyrotropin / Q000097:blood*
chemical_list: D013972:Thyrotropin; D007455:Iodine