Influence of Physiological Selenium on Course of Autoimmune Thyroiditis
Abstract and Introduction
Objective Our study aimed to investigate whether physiological doses of selenium (Se) influence the natural course of autoimmune thyroiditis (AIT).
Design and Patients A total of 76 consecutive patients (65F, 11M, median 43, range 15–75 years) with AIT, normal or slightly elevated TSH and fT4 within the normal range were divided into two groups: Group 0 (30 cases) was given no treatment while Group 1 (46 cases) was treated with sodium selenite 80 μg/day as a single oral dose for 12 months. Thyroperoxidase and thyroglobulin autoantibodies (TPO-Ab; Tg-Ab), TSH, fT4 and urine iodine concentrations (UIC) were measured at baseline and after 6 and 12 months of follow-up. Thyroid ultrasonography (US) was performed at each follow-up point. Echogenicity was measured by histographic analysis of gray-scale pixels (gsp) ranging from 0 = black to 255 = white.
Results Thyroid echogenicity decreased significantly in both groups after 6 months, but after 12 months, it had changed no more in Group 1, whereas it had dropped further in Group 0. No significant variation in TPO-Ab or Tg-Ab levels was observed between the two groups after 6 months, but both values decreased significantly after 12 months in Group 1, and five patients in this group became negative for TPO-Ab. TSH and FT4 showed no significant variations in either group.
Conclusions Dietary supplementation with physiological doses of Se seems to be effective in preventing a reduction in thyroid echogenicity after 6 months of treatment and in reducing TPO-Ab and Tg-Ab after 12 months, but does not modify TSH or FT4.
Selenium (Se) is a trace element contained mainly in plants from which, via vegetable and animal dietary products, it is provided to humans. Being a component of the catalytic site of at least 30 different selenoproteins, it is thought to play a part in a large number of biological processes, such as free radical catabolism, immune response, endocrine function and tumourigenesis.
A daily Se intake of around 55–75 micrograms represents the optimal quantity and because most European soils are poor in this element, a large proportion of people still experience borderline Se deficiency, with consequences that are little understood.
Among all human tissues, the thyroid gland contains the largest amounts of selenium, and Se concentrations at this site are relatively stable irrespective of dietary intake and availability in the organism. Being a cofactor of various selenoproteins, such as glutathione peroxidase enzyme type 3 (GPx-3), 5'-deiodinase isoenzymes (D1, D2), thioredoxin reductases (TRs) and selenoprotein P, Se is involved in several aspects of thyroid homoeostasis, such as cell protection against H2O2 injury and hormone balance. Se status and/or Se deficiency could consequently have a crucial impact, particularly when the immune system is widely triggered and hormone production is impaired, as in autoimmune thyroiditis (AIT). Several prospective randomized studies on patients with AIT have clearly demonstrated that short-term treatment with high doses of Se (200 μg/day) lowered their thyroperoxidase autoantibody levels, and this effect was lost when Se was discontinued, supporting the conviction that Se has a beneficial role in AIT.
This prospective study was designed to study the effect of physiological doses of sodium selenite on the natural course of AIT in Italian patients with normal thyroid function or subclinical hypothyroidism who were not taking L-T4 replacement therapy, with a view to assessing the time-related progression of thyroid cell damage by ultrasonography and serum levels of thyroid autoantibodies and hormones.