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Change in serum TSH levels as a function of iodine intake and thyroid volume - an in-depth evaluation of the study KiGGS
Project
Project code: 2812HS014
Contract period: 01.10.2012
- 13.04.2013
Budget: 10,336 Euro
Purpose of research: Basic research
In various countries iodine prophylaxis measures have improved iodine status 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 hypothy-roidism or a physiologic TSH-adaptation mechanism is not clear. Data on iodine excretion and thyroid status of 6-17 year old children and adolescents, collected 2003-06 in the nationwide KiGGS Study, provided the basis for the analyses of mutual relationships of iodine status (estimated by iodine/creatinine ratio in spot urines), TSH-serum levels and thyroid volume (determined by ultrasound). For statistical analyses in final regression models, only those children were included for whom none of the available parameters (including fT3 and fT4 measurements) suggested pathophysiologic changes in thyroid status (n=6101).In contrast to the conventional doctrine, also in children with healthy thyroid function, urinary iodine excretion (iodine status) was significantly positively associated with TSH (P less than 0.05; adjusted for sex, age, body surface area, BMI, fT3/fT4 ratio and time of blood sampling). Children with better iodine status showed, on average, an about 0.2 µU/mL higher TSH level than children with lower iodine status. Higher TSH-levels were not associated with a higher prevalence of TPO antibodies. In parallel, children with smaller thyroid volume (long-term better iodine supply) had significantly higher TSH levels (P less than 0.001, fully adjusted). Short-term iodine status (spot urine) and thyroid volume were negatively associated in the basic linear regression model (P less than 0.05, adjusted for sex and body surface area); however, this association lost statis-tical significance after full adjustment of the model. Our findings show for the first time that in children with healthy thyroid function, smaller thyroid volumes are 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. Accordingly, an increased TSH level should not be used as the single criterion to evaluate the prevalence of hypothyroidism in a population or to diagnose it in a single person, as TSH levels can also be elevated due to physiological reasons, e.g., simply due to an improved iodine status.
Section overview
Subjects
- Nutritional behaviour
