title: Lower prevalence of mild hyperthyroidism related to a higher iodine intake in the population: prospective study of a mandatory iodization programme.
abstract: OBJECTIVE
  Marked differences in pattern of thyroid dysfunction are seen in populations with different iodine intakes. We evaluated the influence of a higher iodine intake on thyroid hormone levels and the prevalence of thyroid dysfunction in the Danish population.
  
  
  METHODS
  Two cross-sectional studies matched on a group level according to sex and age.
  
  
  METHODS
  In all, 8219 individuals were examined before (n = 4649) or after (n = 3570) the introduction of a mandatory iodization programme in 2000 in two regions with established mild and moderate iodine deficiency. Serum TSH, fT(4) and fT(3 )were measured. An ultrasonography of the thyroid was performed.
  
  
  RESULTS
  We found a higher median serum TSH after the introduction of mandatory iodization of salt: 1.51 mU/l (10-90th percentiles: 0.72-3.00) vs. 1.30 mU/l (10-90th percentiles: 0.59-2.66) before iodization. The difference was found in both regions and across age groups. There was a lower prevalence of mild hyperthyroidism and a tendency towards a lower prevalence of overt hyperthyroidism. The prevalence of mild hypothyroidism increased, most pronounced among young women after iodization. Conversely, there was a lower prevalence of undiagnosed overt hypothyroidism. However, when currently treated participants were included, the prevalence of hypothyroidism increased after iodization in the area with formerly mild iodine deficiency.
  
  
  CONCLUSIONS
  A change in pattern of thyroid dysfunction was seen in relation to mandatory iodization of salt. There was no rise in the prevalence of hyperthyroidism and the prevalence of mild hyperthyroidism was halved. Conversely, prevalence of hypothyroidism increased.
authors.affiliation: Department of Endocrinology and Gastroenterology, Bispebjerg University Hospital, Copenhagen, Denmark. pernille.vejbjerg@regionh.dk
authors.forename: Pernille
authors.initials: P
authors.lastname: Vejbjerg
authors.forename: Nils
authors.initials: N
authors.lastname: Knudsen
authors.forename: Hans
authors.initials: H
authors.lastname: Perrild
authors.forename: Peter
authors.initials: P
authors.lastname: Laurberg
authors.forename: Allan
authors.initials: A
authors.lastname: Carlé
authors.forename: Inge Bülow
authors.initials: IB
authors.lastname: Pedersen
authors.forename: Lone B
authors.initials: LB
authors.lastname: Rasmussen
authors.forename: Lars
authors.initials: L
authors.lastname: Ovesen
authors.forename: Torben
authors.initials: T
authors.lastname: Jørgensen
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D003718:Denmark / Q000453:epidemiology; D005260:Female; D006801:Humans; D006980:Hyperthyroidism / Q000188:drug therapy* / Q000453:epidemiology*; D007455:Iodine / Q000008:administration & dosage*; D008297:Male; D037141:Mandatory Programs; D008875:Middle Aged; D015995:Prevalence; D011314:Preventive Health Services; D015397:Program Evaluation; D011446:Prospective Studies; D017673:Sodium Chloride, Dietary / Q000008:administration & dosage*; D013963:Thyroid Hormones / Q000097:blood; D055815:Young Adult
chemical_list: D017673:Sodium Chloride, Dietary; D013963:Thyroid Hormones; C034024:iodized salt; D007455:Iodine