Many thyroid enzymes are selenoproteins, such as the deiodinases that metabolize thyroid hormones and the glutathione peroxidases (GPX) that help to manage oxidative stress in the thyrocyte.7,10 Reduced selenium levels have been observed in patients with autoimmune thyroid disease, including HT.11 As a result, supplementing selenium in patients with HT has attracted much attention in recent decades. This evidence concerns the gene SELENOS and hematocrit.