Selenium: Selenomethionine, Brazil Nuts & Thyroid Function

Selenium is a trace mineral that is incorporated into selenoproteins — a family of about 25 proteins that include glutathione peroxidases, thioredoxin reductases, and iodothyronine deiodinases. These enzymes are critical for antioxidant defense, thyroid hormone metabolism, and DNA synthesis.

Thyroid Connection

The thyroid gland has the highest selenium concentration per gram of any organ in the body. Selenium-dependent deiodinase enzymes convert the inactive thyroid hormone T4 into the active form T3. Selenium deficiency can impair this conversion even when iodine status is adequate, making selenium a often-overlooked factor in thyroid health.

Selenium is also needed for glutathione peroxidase activity, connecting it to the body's master antioxidant system.

Forms & Food Sources

Selenomethionine (from food) is well-absorbed and can be non-specifically incorporated into body proteins in place of methionine, serving as a selenium reserve. Brazil nuts are famously rich in selenium — just 1-2 nuts per day can meet the entire RDA — but content varies enormously depending on soil selenium levels in the growing region. Fish, organ meats, and whole grains grown in selenium-adequate soil are also good sources.

External resources: NIH — Selenium Fact Sheet