Selenium and goiter prevalence in borderline iodine sufficiency

Design: Selenium (Se) is required for the biosynthesis of selenocysteine-containing proteins. Several selenoenzymes, e.g. glutathione peroxidases and thioredoxin reductases, are expressed in the thyroid. Selenoenzymes of the deiodinase family regulate the levels of thyroid hormones. For clinical investigators, it is difficult to determine the role of Se in the etiology of (nodular-) goiter, because there are considerable variations of Se concentrations in different populations as reflected by dietary habits, bioavailability of Se compounds, and racial differences. Moreover, most previous clinical trials which investigated the influence of Se on thyroid volume harbored a bias due to the coexistence of severe iodine deficiency in the study populations. Methods: Therefore, we investigated the influence of Se on thyroid volume in an area with borderline iodine sufficiency. First, we investigated randomly selected probands for urinary iodine (UI) and creatinine excretion in spot urine samples and determined the prevalence of goiter and thyroid nodules by high-resolution ultrasonography. After this, we determined urinary Se excretion (USc) in probands with goiter as well as in matched probands without goiter. Adjustments between the two compared groups were made for age, gender, history of thyroid disorders, smoking, and UI excretion. Results: The mean USe and UI rates of all 172 probands were 24 mu g Se/l or 27 mu g Se/g creatinine and 96 mu g I/l or 113 mu g I/g creatinine indicating borderline selenium (20-200 mu g/l) and iodine (100-200 mu g/l) sufficiency of the study population. Probands with goiter (n = 89) showed significantly higher USc levels than probands with normal thyroid volume (n=83; P < 0.05). USe rates were not influenced by present smoking or pregnancy. Conclusions: In our investigation, USe was not an independent risk factor for the development of goiter. The higher USe in probands with goiter in comparison with probands with normal thyroid volume is most likely a coincidence. Se does not significantly influence thyroid volume in borderline iodine sufficiency because the iodine status is most likely the more important determinant.