Selenium
trace-mineral
Key Takeaways
- FDA daily value is 55 mcg; RDA for adults is 55 mcg/day
- Constituent of 25 selenoproteins (NIH fact sheet)
- Meta-analysis of 35 RCTs: selenium lowers TSH and TPOAb in Hashimoto thyroiditis (pmid:38243784)
- Deficiency alone rarely causes illness but exacerbates iodine deficiency
- Excess selenium can increase cancer risk in adequate-status individuals (pmid:24857143)
Evidence Spectrum
14 studies reviewed →Hashimoto thyroiditis management
35-RCT meta-analysis: decreased TSH (SMD -0.21) without THRT and reduced TPOAb (SMD -0.96). Moderate evidence certainty.2
Keshan disease prevention
Selenium reduced Keshan disease by 86% in endemic areas. Min 20 mcg/day required.
Cancer risk modification
May reduce cancer in low-Se populations but increased prostate cancer in adequate-Se populations.3
Wound healing
Associated with improved burn wound outcomes alongside other micronutrients.1
14
Studies Reviewed
15 mcg
RDA (0-6 months)
400 mcg/day
Upper Limit
water-soluble
Solubility
Role in the Body
Selenium is a constituent of 25 selenoproteins critical for thyroid hormone metabolism, DNA synthesis, reproduction, and oxidative damage protection. Key selenoproteins include glutathione peroxidases, thioredoxin reductases, and selenoprotein P. Present in foods as selenomethionine and selenocysteine. Readily absorbed regardless of status. About 28-46% found in skeletal muscle. Homeostasis maintained via urinary excretion.
- Antioxidant defense (glutathione peroxidases)
- Thyroid hormone metabolism (T4 to T3)
- DNA synthesis and repair
- Immune function
- Reproductive health
- Oxidative damage protection
Supplement Forms
Selenomethionine
RecommendedBioavailability: 90%
Organic form; well absorbed and stored
Selenocysteine
RecommendedBioavailability: 0%
Functional form in selenoproteins
Sodium selenite/selenate
Bioavailability: 50%
Inorganic; less efficiently retained
Selenium-enriched yeast
RecommendedBioavailability: 80%
Primarily selenomethionine; widely used in trials
Food Sources
Brazil nuts (~68 91 mcg/nut)
Seafood
Organ meats
Eggs
Whole grains
Dairy
Edible insects (pmid:23471778)
Deficiency
Prevalence: Rare in isolation; common in selenium-poor soil regions. Exacerbates iodine deficiency.
Symptoms:
- Keshan disease
- Kashin-Beck disease
- Increased oxidative stress
- Impaired thyroid function
- Weakened immunity
Risk Factors:
- Selenium-poor soils
- Vegan/vegetarian diets (pmid:33341313)
- Bariatric surgery (pmid:34302218)
- CKD
- HIV
- Malabsorption
Safety & Interactions
Possible Side Effects:
- • Selenosis at >400 mcg/day
- • GI discomfort
- • Potential increased prostate cancer risk at adequate status
Drug Interactions:
- • Chemotherapy agents
- • Cisplatin increases requirements
- • Statins may reduce Se levels
Contraindications:
- • Se-sufficient individuals on high doses
- • Non-melanoma skin cancer history
Frequently Asked Questions
How much selenium daily?
RDA is 55 mcg/day. One Brazil nut provides 68-91 mcg.
Selenium for thyroid?
Meta-analysis supports lowering TSH/TPOAb in Hashimoto. Consult your provider.
Can you get too much?
Yes. Upper limit 400 mcg/day. Excess causes selenosis and may increase cancer risk.
Research Sources
15 peer-reviewed studies analyzed from PubMed. 3 directly cited in this review.