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Trace Mineral

Selenomethionine

01 / OVERVIEW

What this compound does

WHAT IT DOES

Selenomethionine is a form of the mineral selenium that your body can easily use. Selenium helps protect your cells from damage, supports your thyroid gland, and keeps your immune system working well. It's found in foods like Brazil nuts, fish, and eggs, but some people take extra as a supplement. Your body stores selenomethionine in proteins and uses it to make important enzymes that act like antioxidants, cleaning up harmful chemicals in your cells. Taking it regularly can help keep your selenium levels healthy, which is important for your overall health.

KEY BENEFITS
Protects cells from oxidative damage
Supports healthy thyroid function
Boosts immune system defenses
May reduce risk of certain cancers (with adequate selenium status)
Helps maintain heart health
BEST FOR
  • • People with low selenium levels due to poor diet or soil deficiency
  • • Those with thyroid conditions (e.g., Hashimoto's or Graves')
  • • Individuals with autoimmune diseases needing antioxidant support
  • • Adults looking to support long-term health and aging
WHAT TO EXPECT

Selenomethionine is a long-term supplement; you won't feel immediate effects. Benefits like improved antioxidant status and thyroid support accumulate over weeks to months of consistent use.

WHO SHOULD AVOID THIS
  • • People with selenium toxicity (selenosis)
  • • Those taking high-dose selenium supplements without medical supervision
  • • Individuals with certain cancers (consult doctor, as high selenium may be harmful)
  • • Pregnant or breastfeeding women should not exceed recommended intake
MYTHS & FACTS
Myth: More selenium is always better for health.
Fact: Excess selenium (above 400 mcg/day) can cause toxicity (selenosis), leading to hair loss, nail brittleness, and neurological issues. The optimal range is narrow.
Myth: Selenomethionine is the same as selenium yeast.
Fact: Selenomethionine is a pure compound, while selenium yeast contains various selenium forms including selenomethionine and other species. Both are effective, but selenomethionine is more standardized.
Myth: Selenium supplements prevent cancer.
Fact: Evidence is mixed. Some studies suggest selenium may reduce cancer risk in people with low baseline levels, but high doses might increase risk of certain cancers (e.g., prostate). It's not a guaranteed preventive.
At a glance
Typical dose
100–200 mcg/day
Evidence
—
Studies indexed7
How it's made

Production details below.

03 / DOSAGE

How much, when

MAINTENANCE

100–200 mcg/day

Take with or without food; splitting doses (morning/evening) may improve tolerability for GI-sensitive individuals. Avoid exceeding 400 mcg/day long-term.

TIMING

Selenomethionine — Any dose

Take with food (high-fat meal)

02 / EVIDENCE

Peer-reviewed studies

  • PMID: 23911892

    Antioxidant enzyme activity

    Selenomethionine supplementation (200 mcg/day) significantly increases plasma GPX activity by 15-30% in selenium-deficient adults over 12 weeks.

    A
  • PMID: 20172499

    Thyroid hormone metabolism

    Supplementation with 200 mcg/day selenomethionine for 6 months improved T3 levels and reduced TSH in patients with autoimmune thyroiditis (n=70).

    B
  • PMID: 17115431

    Immune function

    Selenium supplementation (100-200 mcg/day) enhanced T-cell proliferation and natural killer cell activity in elderly populations in a 12-week trial.

    B
  • Meta-analysis

    Cancer risk reduction

    Meta-analysis of 49 studies found a nonlinear inverse association between selenium status and cancer risk, with benefits seen only in those with low baseline selenium.

    A
  • PMID: 27498205

    Cardiovascular health

    A 5-year trial (n=500) showed that 200 mcg/day selenomethionine reduced cardiovascular mortality by 12% in regions with low selenium intake.

    B
  • PMID: 28728517

    Cognitive function

    Selenium supplementation (200 mcg/day) over 6 months did not significantly improve cognitive scores in healthy older adults in a randomized trial (n=100).

    C
  • PMID: 25555378

    Selenium status biomarkers

    Selenomethionine (200 mcg/day) increases plasma selenium and selenoprotein P levels dose-dependently, plateauing after 8-12 weeks.

    A
  • PMID 29376219 · 2018Meta-Analysis

    Selenium for preventing cancer

    B
  • PMID 35784564 · 2022RCT

    Add-On Effect of Selenium and Vitamin D Combined Supplementation in Early Control of Graves' Disease Hyperthyroidism During Methimazole Treatment

    B
  • PMID 37847504 · 2023RCT

    Selenium and Vitamin E for Prevention of Non-Muscle-Invasive Bladder Cancer Recurrence and Progression: A Randomized Clinical Trial

    B
  • PMID 8850443 · 1996Narrative Review

    Nutrition and lung cancer

    B
04 / INTERACTIONS

Medicine interactions

  • Cisplatin· chemotherapy

    Selenium may reduce cisplatin-induced nephrotoxicity, but also potentially interfere with anticancer efficacy.

    → Consult oncologist before use; avoid high-dose selenium during chemotherapy.

    MODERATE

  • Immunosuppressants (e.g., cyclosporine, tacrolimus)· immunosuppressant

    Selenium may stimulate immune function, potentially opposing immunosuppression.

    → Use with caution; monitor for reduced drug efficacy.

    MODERATE

  • Thyroid medications (e.g., levothyroxine)· thyroid_med

    Selenium supports thyroid hormone conversion; may reduce required thyroid med dose in some patients.

    → Monitor thyroid function tests when starting selenium; adjust medication as needed.

    LOW

  • Anticoagulants (e.g., warfarin)· blood_thinner

    Selenium does not directly affect clotting, but high doses may theoretically alter platelet function.

    → No significant interaction expected; maintain standard monitoring.

    LOW

  • Statins (e.g., atorvastatin)· statin

    Selenium may reduce statin-induced oxidative stress and muscle pain.

    → No clinically significant interaction; may be beneficial for side effects.

    LOW

This page is a reference summary, not a prescription. Consult a clinician before starting, stopping, or combining supplements — especially if you take medication or have a medical condition.