Antioxidant defense
Selenoproteins including glutathione peroxidases (GPx1–4) neutralize hydrogen peroxide and lipid hydroperoxides, protecting cell membranes and DNA from oxidative damage.
Thyroid hormone metabolism
Iodothyronine deiodinases are selenoenzymes that convert inactive T4 to active T3. Selenium deficiency impairs thyroid hormone activation and may accelerate autoimmune thyroid disease.
Immune function
Selenium enhances proliferation of T and NK cells, promotes cytokine production, and supports the oxidative burst in macrophages. Deficiency is associated with increased susceptibility to viral infections.
Cancer risk reduction
Epidemiological studies suggest inverse relationship between selenium status and cancer incidence, particularly colorectal and prostate cancers. Mechanism involves DNA repair and apoptosis induction.
Selenoprotein synthesis
Selenium is incorporated as selenocysteine (the 21st amino acid) into over 25 selenoproteins via a unique UGA codon recoding mechanism. These proteins serve antioxidant, anti-inflammatory, and metabolic functions.
Glutathione peroxidase activation
Selenium is the catalytic center of GPx enzymes that reduce hydrogen peroxide and organic hydroperoxides to water and alcohols using glutathione as the electron donor, directly protecting against oxidative cell damage.
Thioredoxin reductase activity
Selenium-containing thioredoxin reductases maintain thioredoxin in its reduced state, enabling DNA synthesis, peroxiredoxin recycling, and transcription factor regulation.
RCT of 200 mcg/day selenomethionine vs. placebo in 70 patients with autoimmune thyroiditis for 3 months.
70 adults with Hashimoto's thyroiditis. 3-month intervention.
Selenium supplementation significantly reduced anti-TPO antibody titers and improved thyroid ultrasound echogenicity. Well-tolerated with no adverse effects.
Large RCT of selenium (200 mcg/day) and/or vitamin E for prostate cancer prevention in 35,533 men.
35,533 men. Median 5.5-year follow-up.
Neither selenium nor vitamin E alone or in combination reduced prostate cancer incidence. Baseline selenium status likely an important moderator of outcomes.