Selenium

Effects and Benefits

Core Identification

Common Names:
- Selenium
- Se (chemical symbol)
- Selenomethionine (organic amino acid form)
- Sodium selenite (inorganic form)
- Selenium yeast (bioavailable supplement form)

Latin Name: N/A (Chemical element: Se, Atomic number 34)

Category: Mineral (Essential Trace Element)

Uses

Traditional Uses

• Historically recognized through deficiency diseases (Keshan disease in China)
• Traditional consumption of selenium-rich foods (Brazil nuts, seafood) in regions with adequate soil selenium
• Recognition of selenium's importance grew primarily in the 20th century as deficiency diseases were studied

Modern Uses

• Antioxidant protection - Glutathione peroxidase cofactor | Research quality: Strong
• Key findings: Selenium is essential for glutathione peroxidase function, the body's primary antioxidant enzyme that neutralizes hydrogen peroxide and other harmful free radicals before they can damage cells. This protects against degenerative diseases including atherosclerosis, cataracts, arthritis, and cellular damage.

• Source citations: Brewer - TDT Encyclopedia of Vitamins; Lust - The Natural Remedy Bible

• Thyroid function support - Hormone conversion and gland protection | Research quality: Strong

• Key findings: The thyroid gland has the highest concentration of selenium in the body. Selenium-containing enzymes (thyroxine deiodinases) regulate production of the active thyroid hormone T3. Selenium also protects the thyroid from free radical damage generated during hormone production. Where iodine is adequate but selenium is low, thyroid tissue damage and fibrosis can occur. Low selenium increases risk of thyroid conditions including goiter.

• Source citations: Brewer - TDT Encyclopedia of Vitamins; Moyad - The Supplement Handbook

• Immune system enhancement - Natural killer cell stimulation | Research quality: Strong

• Key findings: Selenium stimulates production of natural killer cells that fight viral and bacterial infections and is needed for antibody synthesis. When selenium and vitamin E are taken together, antibody production increases by up to 30 times. Viruses become more virulent when passing through a selenium-deficient host due to increased free radicals encouraging viral mutations.

• Source citations: Brewer - TDT Encyclopedia of Vitamins

• Male fertility support - Sperm motility enhancement | Research quality: Moderate

• Key findings: Selenium is needed for normal testosterone metabolism and testicular development. A unique selenium-containing protein in sperm cells is essential for sperm motility. In one study, subfertile men taking selenium doubled their sperm motility, and 11% successfully fathered a child compared with no conceptions in the placebo group.

• Source citations: Brewer - TDT Encyclopedia of Vitamins

• Autoimmune thyroid conditions - Hashimoto's thyroiditis support | Research quality: Moderate

• Key findings: Studies show 200 mcg selenomethionine can reduce thyroid antibody levels in Hashimoto's thyroiditis and may decrease thyroid hormone replacement dosage needed. Average time to benefit: 7.5 months. The CATALYST trial in Denmark is currently evaluating selenium-enriched yeast for autoimmune thyroiditis.

• Source citations: Moyad - The Supplement Handbook

• Cardiovascular health - Heart muscle protection | Research quality: Moderate

• Key findings: Selenium is important for healthy muscle fibers, including the heart. In parts of China with very low selenium, Keshan disease (a form of heart failure) occurs. Selenium may protect against hardening and furring of arteries, stroke, and heart attack when combined with adequate vitamin E and A.
• Source citations: Brewer - TDT Encyclopedia of Vitamins

Active Compounds

Primary Active Ingredients:
- Selenocysteine - The 21st amino acid; incorporated into selenoproteins including glutathione peroxidase, thioredoxin reductases, and iodothyronine deiodinases
- Selenomethionine - Organic form found in foods and supplements; stored in body proteins and releases selenium as needed
- Glutathione peroxidase - Primary selenium-dependent enzyme that neutralizes hydrogen peroxide and lipid peroxides
- Thyroxine deiodinases - Selenium-containing enzymes that convert T4 to the active T3 thyroid hormone
- Selenoprotein P - Transport protein that carries selenium from the liver to other tissues

Dosage Information

Standard Dosage:
- Form: Tablets, capsules (selenium yeast, selenomethionine, or sodium selenite)
- Amount: 55-70 mcg per day (RDA)
- Frequency: Once daily with food

Therapeutic Dosage:
- Form: Capsules or tablets (selenomethionine or selenium yeast preferred for bioavailability)
- Amount: 100-200 mcg per day
- Purpose: Antioxidant protection, thyroid support, immune enhancement
- Duration: Ongoing; evaluate periodically with healthcare provider

Maximum Safe Dosage:
- Daily maximum: 400 mcg (Tolerable Upper Intake Level)
- Warning threshold: Toxicity can occur above 800 mcg daily; some sources cite 450 mcg as safe upper limit

Bioavailability Notes:
- Selenium bound to yeast (selenium yeast) is readily bioavailable and well-absorbed
- Selenomethionine is an organic form that integrates into body proteins
- Sodium selenite is an inorganic form with slightly lower bioavailability
- Brazil nuts are extremely rich—2 nuts per day can provide adequate intake

How to Take It

Timing:
- Take with food for optimal absorption
- Morning or evening; consistency matters more than specific timing
- Can be taken with other antioxidants (vitamin E enhances effects)

Synergies - What It Works Well With

Complementary Supplements:
1. Vitamin E - Works synergistically to protect unsaturated fatty acids in membranes and cells from oxidation; combined, they can increase antibody production by up to 30 times | Enhanced antioxidant and immune protection
2. Iodine - Both required for optimal thyroid function; selenium protects thyroid from damage while iodine is needed for hormone synthesis | Complete thyroid support
3. N-Acetyl Cysteine (NAC) - Combines with selenium to synthesize glutathione, the body's master antioxidant | Enhanced glutathione production
4. Vitamin A - Works with selenium to reduce cancer risk; combined deficiency significantly increases various cancer risks | Synergistic protective effects
5. Vitamin C - Fellow antioxidant that works through complementary mechanisms | Comprehensive antioxidant coverage
6. Zinc - Both trace minerals support immune function and thyroid health | Complementary immune and thyroid support

Avoidance - What NOT to Combine With

Supplement Interactions:
1. High-dose selenium with high-dose vitamin C - Very high doses of vitamin C may theoretically reduce selenium absorption; generally not a concern at normal doses

Drug Interactions:
1. Chemotherapy drugs (cisplatin, doxorubicin) - Selenium may provide protective effects against drug toxicity; consult oncologist before use as very high doses (4,000 mcg) used in studies require medical supervision | Potential protective interaction requiring monitoring | Severity: Consult physician
2. Clozapine (antipsychotic) - This drug can decrease blood selenium levels; supplementation may be beneficial but should be monitored | Potential depletion | Severity: Moderate
3. Statins (HMG-CoA reductase inhibitors) - No direct interaction, but selenium is part of the antioxidant network that may be affected by statin-induced CoQ10 depletion | Monitor overall antioxidant status | Severity: Mild

Food Interactions:
- No significant food interactions
- High-dose zinc supplements taken long-term may theoretically affect selenium status

Safety Information

Contraindications:
- Known selenium hypersensitivity
- Individuals already consuming very high selenium from diet (rare)
- Those with elevated skin cancer risk or history of skin cancer recurrence should be cautious with higher doses (200+ mcg)
- Those at elevated diabetes risk should discuss higher doses with healthcare provider

Side Effects:
- At standard doses (55-200 mcg): Generally well-tolerated with minimal side effects similar to placebo
- At excessive doses (800+ mcg): Selenosis symptoms include garlic odor on breath (from dimethyl selenide), fragile or black fingernails, metallic taste in mouth, dizziness, nausea, hair loss
- Early toxicity signs: Peeling fingernails, brittleness of hair

Long-Term Use:
- Standard doses (up to 200 mcg) considered safe for long-term use
- Intakes above 400 mcg daily not recommended without medical supervision
- Recent research (SELECT trial) found 200 mcg daily may increase prostate cancer risk in men, particularly those with already adequate or high dietary selenium intake
- Periodic evaluation recommended for therapeutic dosing

Special Precautions:
- Pregnancy: Important for fetal development; low levels associated with increased miscarriage risk; stick to standard doses unless directed otherwise
- Smokers: Studies show 150-200 mcg daily associated with 25% lower risk of lung and other cancers; benefit does not increase with higher doses
- Men concerned about prostate health: Discuss supplementation carefully with healthcare provider given recent SELECT trial findings showing potential increased risk
- Those with autoimmune conditions: May help reduce thyroid antibodies in Hashimoto's but requires monitoring

Primary Uses At-a-Glance

Primary:
- Antioxidant protection (glutathione support)
- Thyroid function support
- Immune system enhancement

Secondary:
- Male fertility support
- Cardiovascular protection
- Autoimmune thyroid conditions (Hashimoto's)
- Chemotherapy support (under medical supervision)

Sources

Local Library:
- Brewer, Sarah - TDT Encyclopedia of Vitamins
- Weil, Andrew - Eating Well for Optimum Health
- Lust, John - The Natural Remedy Bible
- Moyad, Mark - The Supplement Handbook
- Gaby, Alan R. - A-Z Guide to Drug-Herb-Vitamin Interactions
- Balch, Phyllis - Prescription for Herbal Healing
- Bartram, Thomas - Bartram's Encyclopedia of Herbal Medicine
- Moline, Peg - The Doctors Book of Natural Health Remedies

General Knowledge:
- Institute of Medicine Dietary Reference Intakes
- SELECT trial findings (Selenium and Vitamin E Cancer Prevention Trial)