Selenium (Se)
Selenocysteine, Glutathione Peroxidase & Thyroid Deiodinases. Selenium is incorporated genetically into 25 human selenoproteins as selenocysteine (the 21st amino acid), operating at the catalytic center of glutathione peroxidases, thioredoxin reductases, and iodothyronine deiodinases.
How Selenium Works in Your Body
Selenium is required for critical enzymatic, structural, and electrochemical processes throughout the body:
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Selenocysteine Catalysis
Encoded by UGA stop codons paired with a SECIS element, selenocysteine contains a selenol group (-SeH) that is ionized at physiological pH, conferring far higher catalytic nucleophilic activity than cysteine.
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Hydroperoxide Detoxification
Catalytic core of glutathione peroxidases (GPx1-4), reducing toxic hydrogen peroxide and lipid hydroperoxides to water and non-toxic lipid alcohols, halting atherogenesis and cellular senescence.
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Thyroid Prohormone Activation
Active site of iodothyronine deiodinases (DIO1, DIO2), removing an outer-ring iodine atom to convert inactive prohormone T4 into active T3 in peripheral tissues.
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Thioredoxin System
Powers thioredoxin reductases (TrxR), regenerating reduced thioredoxin for DNA synthesis and cellular redox equilibrium.
How Much Do You Need? (Daily Dietary Targets)
Recommended daily intake guidelines and safe upper limits for adults:
| Group / Life Stage | Recommended Target | Practical Advice |
|---|---|---|
| Adult Men | 55 mcg/day | Maintains normal cellular saturation, fluid balance, and enzyme function. |
| Adult Women | 55 mcg/day | Calibrated to balance menstrual needs, bone remodeling, and hormonal health. |
| Pregnancy & Lactation | 60 mcg/day (Preg) / 70 mcg/day (Lact) | Supports fetal development and replaces minerals transferred during breastfeeding. |
| Tolerable Upper Limit (UL) | 400 mcg/day | The highest chronic daily intake safe from precipitating organ distress or toxicity. |
Top Whole Food Sources
| Food Item | Serving Size | Nutrient Content | Relative Daily Density |
|---|---|---|---|
| Brazil Nuts (dried) | 1 nut (5g) | 96 mcg | |
| Yellowfin Tuna (cooked) | 3 oz (85g) | 92 mcg | |
| Halibut (cooked) | 3 oz (85g) | 47 mcg | |
| Sardines (canned in oil) | 3 oz (85g) | 45 mcg | |
| Egg (whole hard-boiled) | 2 large | 30 mcg |
Signs You're Getting Too Much (Chronic Excess)
Consuming excess quantities through high-dose supplements or impaired kidney excretion can trigger side effects:
- Selenosis (Narrow Therapeutic Window): Ingestion exceeding 400-800 mcg/day chronically produces selenosis.
- Characteristic Garlic Breath: Volatile dimethyl selenide is excreted through pulmonary alveoli, creating an unmistakable garlic odor on breath and perspiration.
- Alopecia & Onycholysis: Hair becomes brittle and falls out; fingernails develop transverse white lines, become deformed, and slough off.
- Neurotoxicity: Peripheral paresthesias, hyperreflexia, hemiplegia, fatigue, and severe gastrointestinal distress.
Signs You're Not Getting Enough (Chronic Deficiency)
Prolonged low intake or excessive mineral loss produces progressive clinical complications:
- Keshan Disease: Endemic juvenile cardiomyopathy characterized by multifocal myocardial necrosis and congestive heart failure, triggered by coxsackievirus infection in selenium-deficient populations.
- Kashin-Beck Disease: Chronic disabling osteochondropathy characterized by bilateral symmetrical atrophy and necrosis of growth plate chondrocytes, leading to enlarged joints and shortened limbs.
- Impaired Thyroid Metamorphosis: Defective peripheral conversion of T4 to T3, amplifying iodine deficiency and hypothyroid symptoms.
- Immune Deterioration: Loss of GPx antioxidant shielding triggers accelerated viral mutation rates and elevated viral virulence.
Discover Synergistic Food Pairings
Learn which nutrients enhance the absorption of Selenium and which competing minerals you should avoid taking simultaneously.
View Nutrient Synergy Matrix →