Thyroid function and prevalence of anti-thyroperoxidase antibodies in a population with borderline sufficient iodine intake: influences of age and sex.
BACKGROUND
We present a large European population-based study of thyroid function, performed in a population with longstanding borderline sufficient iodine intake.


METHODS
The Nijmegen Biomedical Study is a population-based survey conducted in the eastern part of The Netherlands. Randomly selected inhabitants received a postal questionnaire on lifestyle and medical history, which was filled out by 9371 individuals (41.7%). We measured serum thyroid-stimulating hormone (TSH), free thyroxine (FT4), and anti-thyroperoxidase antibodies (TPOAbs) in 6434 responders. A reference population of 5167 individuals was selected by excluding those at risk for thyroid disease.


RESULTS
Overt thyrotoxicosis was found in 0.4% of the total population and subclinical thyrotoxicosis in 0.8%. Overt hypothyroidism was found in 0.4% and subclinical hypothyroidism in 4.0%. In individuals older than 60 years, mean FT4 concentrations increased with age. Mean TSH decreased with age, from 1.46 mIU/L at 18-24 years to 1.07 mIU/L after 85 years. The mean TSH in the total population did not differ from the mean TSH in the reference population; the exclusion of those at risk for thyroid disease, however, lowered the upper limit of the TSH reference interval considerably. In the total population, 8.6% of males and 18.5% of females had positive TPOAbs. The presence of TPOAbs was associated with abnormally high and low TSH concentrations.


CONCLUSIONS
In inhabitants of the eastern part of The Netherlands, serum TSH gradually decreases with age, whereas after age 60, serum FT4 increases, possibly because of the development of thyroid autonomy after longstanding borderline sufficient iodine intake.
Hoogendoorn
Elizabeth H
EH
Department of Endocrinology, Radboud University Nijmegen Medical Centre, Nijmegen, The Netherlands. e.hoogendoorn@endo.umcn.nl
Hermus
Ad R
AR
de Vegt
Femmie
F
Ross
H Alec
HA
Verbeek
Andre L M
AL
Kiemeney
Lambertus A L M
LA
Swinkels
Dorine W
DW
Sweep
Fred C G J
FC
den Heijer
Martin
M
D000293:Adolescent; D000328:Adult; D000367:Age Factors; D000368:Aged; D000369:Aged, 80 and over; D001323:Autoantibodies / Q000097:blood*; D005260:Female; D006801:Humans; D007037:Hypothyroidism / Q000453:epidemiology / Q000503:physiopathology; D007453:Iodide Peroxidase / Q000276:immunology*; D007455:Iodine / Q000008:administration & dosage*; D008297:Male; D008875:Middle Aged; D009426:Netherlands / Q000453:epidemiology; D012016:Reference Values; D012737:Sex Factors; D011795:Surveys and Questionnaires; D013959:Thyroid Diseases / Q000453:epidemiology / Q000503:physiopathology*; D013960:Thyroid Function Tests; D013961:Thyroid Gland / Q000503:physiopathology*; D013971:Thyrotoxicosis / Q000453:epidemiology / Q000503:physiopathology; D013972:Thyrotropin / Q000097:blood; D013974:Thyroxine / Q000097:blood
D001323:Autoantibodies; D013972:Thyrotropin; D007455:Iodine; D007453:Iodide Peroxidase; D013974:Thyroxine