Exp Clin Endocrinol Diabetes 2013; 121 - OP6_39
DOI: 10.1055/s-0033-1336648

Iodine status dependent changes of TSH serum levels – a deeper analysis of the representative KiGGS sample of German children and adolescents

SA Johner 1, M Thamm 2, E Kriener 3, H Völzke 4, R Gärtner 5, U Nöthlings 6, T Remer 1
  • 1IEL-Ernährungsepidemiologie, Universität Bonn, DONALD Studie am Forschungsinstitut für Kinderernährung, Dortmund, Germany
  • 2Robert Koch Institut Berlin, Abteilung für Epidemiologie und Gesundheitsberichterstattung, Berlin, Germany
  • 3Landratsamt Würzburg, Gesundheitsamt, Würzburg, Germany
  • 4Universität Greifswald, Institut für Community Medicine, SHIP/Klinisch-Epidemiologische Forschung, Greifswald, Germany
  • 5Medizinische Klinik Innenstadt der Universität München, Abteilung Endokrinologie und Diabetologie, München, Germany
  • 6Universität Bonn, IEL-Ernährungsepidemiologie, Bonn, Germany

Aims: Worldwide, in various countries, iodine prophylaxis measures improve iodine status (IS) of the population. In some studies, an increase of thyroid stimulating hormone (TSH) levels has been observed coinciding with the prophylaxis. Whether this implies an increased risk for hypothyroidism or a physiologic TSH-adaptation mechanism is not clear.

Methods: Data on IS and thyroid status of 6 – 17 year old children and adolescents, collected 2003 – 06 in the nationwide KiGGS Study (Robert Koch Institute Berlin), provided the basis for the analyses of mutual relationships of IS (estimated by iodine/creatinine ratio in spot urines), TSH-serum levels and thyroid volume (determined by ultrasound). For regression analyses, only those children were included for whom none of the available parameters (including fT3 and fT4 measurements) suggested a pathophysiologic thyroid status.

Results: Median iodine excretion of the investigated KiGGS-subsample (n = 8010) of 121 µg/L suggested an adequate iodine status. Preliminary regression analyses (adjusted for sex, age, time and body surface area) demonstrated a positive association between IS and TSH levels (P < 0.0001). IS was, in addition, inversely associated with thyroid volume (P < 0.05). Thyroid volume showed a significant inverse association with TSH levels (P < 0.0001).

Conclusions: Provided these results can be confirmed in additional (subgroup-)analyses of the KiGGS sample, our findings show for the first time in children that a smaller thyroid volume is associated with higher TSH-levels. A decreased thyroid cell mass and cell amount, as induced by an improved iodine supply, presumably requires adaptively a higher TSH signal to maintain a constant thyroid hormone production. These insights can contribute substantially to dispel uncertainties about the safety of iodine prophylaxis measures, stemming from the observed parallel increases of iodine supply and TSH levels (frequently misinterpreted as increased risk for hypothyroidism).