🧬 Family & Essentiality

🌿 Plain-Language Summary

Selenium is a critical trace mineral for antioxidant defence, thyroid hormone regulation, and immune function. Levels in food depend strongly on soil selenium, which varies by region. Both deficiency and excess can impact health.

⚗️ Molecular & Chemical IDs

• Element: Se (Selenium)
• Atomic number: 34
• Common dietary forms: selenomethionine (plants), selenocysteine (animal foods)

⚡ Functions

• Antioxidant defence: key component of glutathione peroxidase enzymes
• Thyroid metabolism: required for deiodinases that activate/inactivate thyroid hormones
• Immune function: supports immune cell activity
• Redox control: incorporated into selenoproteins regulating oxidative stress

🍽️ Absorption & Bioavailability

🥗 Food Sources

• Seafood (fish, shellfish)
• Meats, eggs, dairy
• Brazil nuts (very high but highly variable in selenium — one nut may exceed daily needs)
• Grains and legumes (content depends on soil selenium)

🇦🇺 Australian NRVs (NHMRC)

• RDI (Men): 70 µg/day
• RDI (Women): 60 µg/day
• Pregnancy: 65 µg/day
• Lactation: 75 µg/day
• UL (Adults): 400 µg/day

🚨 Deficiency & Excess

Deficiency

Rare in Australia, but linked with Keshan disease (cardiomyopathy) in low-selenium regions. Can impair immune function and disrupt thyroid activity.

Excess (Selenosis)

Occurs with very high intakes or over-supplementation. Symptoms include hair/nail brittleness or loss, GI upset, metallic/garlic breath, and neuropathy.

🧪 Testing & Monitoring

• Serum/plasma selenium (routine use)
• Selenoprotein P — used in advanced or research settings
• Consider soil/food variability in interpretation

🔄 Interactions

• High selenium supplement use may affect thyroid hormone balance
• Potential medication interactions — medical guidance advised with high-dose use
• Synergistic with vitamin E in antioxidant defence

📊 Evidence Snapshot

• 🔬✅ Well-established: Antioxidant role (glutathione peroxidase); thyroid hormone metabolism
• 🧪⚖️ Mixed: Supplement benefits depend on baseline selenium status
• ⚠️❌ Unproven/hype: Routine supplementation for cancer prevention or “immune boosting”