Selenium as an essential trace element is capable of exerting complex effects on the endocrine and immune system by its antioxidant capacity. The role of selenium is important because the level of free oxygen radicals is elevated in the physiological thyroid hormone synthesis. The aim of study: Was to determine whether selenium therapy can influence the level of antithyroid peroxidase and antithyroglobulin antibodies or whether there is a correlation between antioxidant capacity and the titer of autoantibodies. Method: 132 patient with autoimmune thyroiditis were investigated in a prospective, blind and placebo-controlled study. L-thyroxine substitution therapy was made in both groups and the level of TSH remained in the normal range. The selenium-treated group (n = 70 patients, 68 female, mean age 41,4 ± 9,5 year) was compared with the placebo-treated group (n = 62 patients, 61 female, mean age 42,7 ± 8,3 year). Selenium therapy was continued by L-seleno-methionine (per os 2 × 100 μg/day) for one year. Determination of TSH, fT4, fT3 and autoantibodies was carried out by chemiluminescence method. Total antioxidant capacity was determined by Randox kit, the level of selenium in the sera by atomic absorption technique was measured. In the follow-up study, patients were controlled every third month and at the end of a one-year observation period. Results: The level of selenium in the untreated patients was significantly lower than in treated patients and controls. The fT3/fT4 ration proved to be higher in patients after selenium therapy. The titer of antithyroid antibodies (mostly the antithyroid peroxidase) significantly decreased at the end of the study. An inverse correlation was found between antioxidant capacity and the level of antithyroid peroxidase antibodies. The volume of thyroid gland slightly diminished in treated patients. Side effects were not observed. Conclusions: Selenium completed with L-thyroxine is a suitable therapy for patients with autoimmune thyroiditis.
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