Lower prevalence of mild hyperthyroidism related to a higher iodine intake in the population: prospective study of a mandatory iodization programme.
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.
Vejbjerg
Pernille
P
Department of Endocrinology and Gastroenterology, Bispebjerg University Hospital, Copenhagen, Denmark. pernille.vejbjerg@regionh.dk
Knudsen
Nils
N
Perrild
Hans
H
Laurberg
Peter
P
Carlé
Allan
A
Pedersen
Inge Bülow
IB
Rasmussen
Lone B
LB
Ovesen
Lars
L
Jørgensen
Torben
T
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
D017673:Sodium Chloride, Dietary; D013963:Thyroid Hormones; C034024:iodized salt; D007455:Iodine