Effects of increased iodine supply on the selenium status

Essential trace elements are functional, structural and regulatory components of a number of bio-molecules that play a vital role in the metabolism of living organisms. In order to synthesize them, trace elements must be available in a correspond-ing chemical form and concentration (Underwood and Suttle, 1999). Biological functions of iodine are mediated chiefly by its impact on the thyroid gland. Its insufficiency is manifested by a development of goitre, abortions and stillbirths. It negatively affects offspring vital-ity, growth and development, adult animal health and production, and it also influences the immune system (Bires et al., 1996; Sargison et al., 1998; Slosarkova et al., 1999; Underwood and Suttle, 1999). However, other elements such as selenium, iron and zinc affect the thyroid gland metabolism and thus also the levels of thyroidal hormones in the organism (Zimmermann and Kohrle, 2002). Selenium affects the thyroid gland metabolism and its hormones both by deiodinases that regu-late the synthesis and degradation of the biologi-cally active thyroid gland hormone (T3) and by selenoperoxidases that protect the thyroid gland from hydroperoxide produced during the synthe-sis of thyroid hormones (Hess and Zimmermann, 2004). Deiodinases are selenoproteins regulating thyroxine conversion (T4) into the biologically ac-tive form 3,3´,5-triiodothyronine (T3) or reverse triiodothyronine (rT3) – inactive hormone of the thyroid gland (Arthur et al., 1990; Larsen and Berry, 1995; Kohrle, 2000; Birringer et al., 2002). Seleniu