Understanding Selenium: Uses and Side Effects on Health

Selenium is a trace mineral essential for many body functions. It’s found naturally in foods and also available as a dietary supplement. In this article, we’ll explore selenium uses, benefits, potential risks, and when to talk with a healthcare provider.

What Is Selenium?

• A micronutrient required in very small amounts
• Incorporated into proteins (selenoproteins) with antioxidant and hormone-regulating roles
• Recommended Dietary Allowance (RDA) for adults: ~55 µg/day
• Tolerable Upper Intake Level (UL): 400 µg/day

Dietary Sources of Selenium

• Brazil nuts (one or two nuts can meet daily needs)
• Seafood (tuna, halibut, shrimp)
• Meats (beef, chicken, turkey)
• Grains and seeds (brazil nuts, whole wheat bread)
• Dairy and eggs

Selenium content in plant foods varies by soil levels.

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Key Selenium Uses in the Body

1. Antioxidant Defense

   • Component of glutathione peroxidase, an enzyme that neutralizes harmful free radicals
   • Helps protect cells from oxidative stress

2. Thyroid Hormone Metabolism

   • Selenium-dependent enzymes (deiodinases) convert the inactive thyroid hormone (T4) into its active form (T3)
   • Supports healthy metabolism, energy levels, and temperature regulation

3. Immune Function

   • Enhances proliferation of T cells and natural killer cells
   • May reduce severity of certain viral infections

4. Reproductive Health

   • Important for sperm motility and male fertility
   • Supports healthy pregnancy outcomes

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Selenium Uses in Disease Prevention and Therapy

Cancer Prevention

• Early trials suggested possible protective effects against prostate, lung, and colorectal cancers.
• A 2018 Cochrane review (Vinceti et al.) concluded there’s no clear evidence that selenium supplements prevent cancer in people with adequate selenium levels.
• Current guidelines do not recommend selenium supplementation solely for cancer prevention.

Type 2 Diabetes Risk

• The Nutritional Prevention of Cancer (NPC) trial sparked interest in selenium and diabetes.
• A 2007 long-term supplementation study (Stranges et al.) found higher selenium intake (~200 µg/day) was associated with a small increase in diabetes incidence.
• If you have diabetes risk factors, discuss selenium doses with your doctor.

Viral Infections and Immune Support

• Low selenium status has been linked to more severe HIV and viral hepatitis outcomes.
• Supplementation may benefit people with documented deficiency, but routine high-dose use isn’t broadly recommended.

Liver Health

• Some research is exploring selenium’s role in non-alcoholic fatty liver disease (NAFLD).
• Non-invasive techniques like transient elastography (e.g., FibroScan®) assess liver stiffness; selenium status may correlate with fibrosis, but more studies are needed.

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Signs of Selenium Deficiency

• Keshan disease (rare cardiomyopathy in low-selenium regions)
• Kashin-Beck disease (joint and bone abnormalities)
• Weakened immune response
• Fatigue or muscle weakness

Deficiency is uncommon in areas with selenium-rich soil or when eating a varied diet.

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Potential Side Effects and Toxicity

Taking too much selenium (above the UL of 400 µg/day) can lead to selenosis. Symptoms may include:

• Garlic-like odor on breath
• Hair and nail brittleness or loss
• Gastrointestinal upset (nausea, diarrhea)
• Skin rash or irritability
• Peripheral neuropathy (numbness, tingling)

Chronic excessive intake may also interfere with cholesterol levels and blood sugar control.

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Recommended Intake and Supplementation Tips

• Adults: RDA 55 µg/day; UL 400 µg/day
• Pregnancy & breastfeeding: RDA 60–70 µg/day
• Supplement forms: selenomethionine, sodium selenite, sodium selenate
• Best approach: aim for dietary sources first; use supplements only if blood tests show deficiency or if advised by a healthcare professional

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Drug Interactions and Precautions

• Anticoagulants (e.g., warfarin): selenium may affect clotting
• Chemotherapy or radiation therapy: discuss timing and doses
• Chronic conditions: thyroid disorders, kidney disease, or heart failure warrant tailored selenium advice

Always disclose all supplements and medications to your healthcare provider.

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Monitoring Your Health

If you’re on selenium supplements, watch for early signs of toxicity. Conversely, if you suspect deficiency (e.g., persistent fatigue, frequent infections), ask your doctor about a blood selenium test.

You might also consider doing a free, online symptom check for High blood pressure if you experience headaches, dizziness, or blurred vision—some studies link selenium status to blood pressure regulation.

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When to Speak to a Doctor

• Life-threatening or serious symptoms (chest pain, severe rash, breathing difficulty): seek immediate care
• Persistent mild symptoms (hair loss, unusual bruising, tingling hands or feet): schedule a medical evaluation
• Before starting high-dose supplements or if you have chronic health conditions: get personalized guidance

Always follow your doctor’s recommendations and report any new or worsening symptoms promptly.

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Take-Home Messages

• Selenium is vital for antioxidant defense, thyroid health, immune function, and fertility.
• “Selenium uses” extend to experimental cancer prevention and viral defense, but high-dose supplements show no clear benefit and may carry risks.
• Avoid exceeding 400 µg/day to prevent toxicity (selenosis).
• Prefer dietary sources; supplement only under medical supervision.
• If you suspect selenium imbalance or have related health concerns, speak to a doctor for testing and tailored advice.

Your health matters—make informed choices and partner with your healthcare team to optimize selenium intake safely.