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    Selenium

    With meals

    Selenium is an essential trace mineral found naturally in Brazil nuts, seafood, and organ meats. It serves as a critical cofactor for selenoproteins, a family of enzymes involved in antioxidant defense, thyroid hormone regulation, and immune signaling. While most people obtain adequate selenium through diet, soil depletion in certain regions can lead to suboptimal intake.

    Research Evidence
    Reduces oxidative stress via glutathione peroxidase activity
    Strong
    Potential mood and cognitive benefits in deficient individuals
    Limited
    Supports innate and adaptive immune responses
    Moderate
    May reduce prostate cancer risk in selenium-deficient populations
    Limited
    May lower thyroid antibody levels in Hashimoto's thyroiditis
    Moderate
    Supports thyroid hormone conversion (T4 to T3)
    Strong
    Source: Examine.com

    Expert Evidence

    8 references from 3 experts

    “One of the best ways to support the thyroid system and metabolism in general is to make sure you're getting enough selenium. Brazil nuts, one or two or three of those per day, you'll have more than enough selenium.”

    How to Lose Fat with Science-Based Tools

    17:47
    2025
    2024
    2021
    2014
    Safety & Cautions

    Side Effects

    • Garlic-like breath odor at high doses
    • Nausea or GI discomfort
    • Hair and nail brittleness with chronic excess
    • Selenosis (toxicity) from prolonged intake above 400 mcg/day
    Selenium has a relatively narrow therapeutic window compared to other minerals, so staying within recommended doses is important. It is generally well-tolerated at 100–200 mcg/day, but long-term megadosing can lead to toxicity symptoms including fatigue, irritability, and peripheral neuropathy.
    Pairs Well With
    Vitamin EZincIodineVitamin C