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Selenium for Health & Longevity

Created on 11/02/2026 – Quick Reference based on Evidence Review created using AI4L / Opus 5.5 – Audit

Selenium, an essential trace mineral, is taken as a dietary supplement for thyroid health and cancer prevention. Correcting a shortfall may help; for adults who already eat enough, large trials found no protection against cancer, heart disease, dementia or early death. It eases mild thyroid-related eye disease. Supplements are linked to a modestly higher chance of diabetes, more hair loss and, at high doses, higher death rates. (Full Review)

Protocol

Repletion-only approach
About 50 µg/day
On top of a typical 55 µg/day diet; benefit expected only with low status (plasma selenium below about 125 µg/L)
Form
Selenomethionine or selenium yeast
Raise plasma selenium; selenite does not
Mild Graves' orbitopathy
100 µg sodium selenite twice daily
For six months
Time to effect
Graves' orbitopathy
By six months
Improvement persisted six months after treatment ended
Thyroid antibodies
By 12 months
Antibody falls appeared; no quality-of-life benefit
Plasma selenium
About 10 weeks
Steady state reached

Benefits

Contraindications
  • People with plasma selenium at or above about 125 µg/L; men with toenail selenium at or above the 60th percentile
  • People with prediabetes or a high diabetes risk
  • People with prior nonmelanoma skin cancer
  • People with untreated iodine deficiency
  • Anyone, including pregnant and breastfeeding women, whose total intake would exceed 255 µg/day
    •
Key Interactions
  • Simvastatin plus niacin (cholesterol-lowering drugs): less cardiovascular protection with antioxidant mixtures including selenium
  • Cisplatin (platinum chemotherapy): altered toxicity; effects on tumor response are untested
  • Vitamin E (supplement): higher prostate cancer risk in men with low selenium status
  • High-dose vitamin C taken with sodium selenite: lower absorption
  • Mercury exposure: greater mercury excretion; clinical effects untested
  • Other selenium sources (multivitamins, Brazil nuts): additive exposure
    •
Theoretical (inferred from mechanism)
  • Anticoagulants and antiplatelet drugs (drugs that slow clotting: warfarin, aspirin): possible added bleeding tendency
  • Statins (atorvastatin, simvastatin): possibly lower selenoprotein production
  • Chelation therapy (DMSA, dimercaptosuccinic acid, and EDTA, ethylenediaminetetraacetic acid, both metal-binding drugs) and cadmium exposure: possibly altered chelation effectiveness or selenium availability
    •

Risk & Side Effects

  • High:
  • Medium: Type 2 diabetes; alopecia, dermatitis and selenosis from selenium excess; high-grade prostate cancer in men with high baseline selenium; higher all-cause mortality at 300 µg/day; squamous cell skin cancer in people with prior skin cancer
    •
  • Low: Adverse blood lipid changes at higher doses; worsened hypothyroidism with coexisting iodine deficiency; higher systolic blood pressure
    •
  • Speculative: Pro-oxidant cell damage at high doses
    •

Monitoring

Marker Target Why
Plasma or serum selenium About 125 µg/L, the selenoprotein saturation point Safety check against excess
HbA1c 4.0–5.6% Safety check for a glucose rise
Fasting glucose Not specified in the ER Paired with HbA1c
Blood pressure No established target; change from own baseline Safety check for the systolic rise
TSH 0.4–4.0 mIU/L Response in thyroid autoimmunity
Free thyroxine Not specified in the ER Paired with TSH in thyroid autoimmunity
TPOAb Below about 35 IU/mL, varies by assay Response in thyroid autoimmunity

Cadence: Baseline before starting; at 3 months, when plasma selenium has reached steady state; then every 6–12 months while supplementation continues. Thyroid markers only with thyroid autoimmunity.

Qualitative Assessment

  • Hair shedding or thinning (early selenosis sign)
  • Nail brittleness, white spots or discoloration
  • Garlic odor on breath or skin
  • Skin rash or new skin lesions
  • Fatigue, irritability or gastrointestinal upset
  • Energy, cold tolerance and mood in thyroid autoimmunity
  • Eye discomfort, swelling or double vision in Graves' orbitopathy
Not medical advice. Educational distillation of a single evidence review. Confirm any decision with a qualified clinician, especially in the presence of prescription drugs or chronic conditions.