A
Grade A💊 100-200mcg daily🎯 10 primary uses🔗 3 synergies⚠️ Review warnings
Levels upNutrition+50 pts
Overview
Essential trace mineral for glutathione peroxidase activity, thyroid function, and optimal immune response to viral infections.
Primary Uses
Antioxidant enzyme supportThyroid functionViral immunitySelenoprotein productionT4 to T3 conversionThyroid protectionAutoimmune thyroid (Hashimoto's)Prostate healthAntioxidantProstate cancer (controversial)
Frequently Asked About Selenium
How much Selenium should I take?
The typical effective range is 100-200 mcg selenomethionine. Individual needs vary based on age, body weight, diet, and goals — start at the lower end and adjust based on response. Always consult a healthcare provider before starting a new supplement.
When is the best time to take Selenium?
With meals. Consistency matters more than perfect timing — pick a daily anchor (e.g. with breakfast or before bed) and stick with it.
Should I take Selenium with food?
Yes.
What is the best form of Selenium?
Selenomethionine is generally the best-absorbed form (Selenium bound to methionine amino acid). Cheaper forms exist but often deliver less usable Selenium per dose.
Does Selenium interact with medications?
Yes — known interactions include May affect thyroid medication needs. If you take any prescription medication, talk to your doctor or pharmacist before starting Selenium.
What does Selenium pair well with?
Selenium stacks well with Iodine, Zinc, and Vitamin E — these combinations either improve absorption or work synergistically toward common goals.
Who should not take Selenium?
Selenium should be avoided or used with caution by people with Excessive supplementation. Pregnant or breastfeeding women should consult a healthcare provider before use.
Compare Forms
4 formsDifferent chemical forms vary in absorption, side effects, and best use cases. Higher bioavailability scores indicate better absorption.
Selenomethionine
HIGH 100Selenium bound to methionine amino acid
Best for:General supplementationBuilding selenium stores
💡 Excellent. Well-absorbed and stored in body proteins.
✅ Pros
- • Best absorbed
- • Builds stores
- • Natural form
⚠️ Cons
- • Can accumulate - don't exceed RDA long-term
📝 Best for maintaining selenium status
Methylselenocysteine
HIGH 95Methylated selenium compound
Best for:Cancer prevention researchDetoxification
💡 Excellent. Unique metabolism pathway.
✅ Pros
- • Unique benefits
- • Cancer research
- • Well-tolerated
⚠️ Cons
- • More expensive
- • Less common
📝 Research-backed for specific applications
Selenium Yeast
HIGH 85Selenium-enriched yeast
Best for:Food-based supplementation
💡 Good. Multiple selenium forms.
✅ Pros
- • Food-based
- • Multiple forms
- • Well-absorbed
⚠️ Cons
- • Yeast sensitivity
- • Variable content
📝 Good option for food-form preference
Sodium Selenite
GOOD 70Inorganic selenium form
Best for:Budget optionShort-term use
💡 Moderate. Pro-oxidant at high doses.
✅ Pros
- • Inexpensive
⚠️ Cons
- • Pro-oxidant potential
- • Lower retention
- • Less natural
📝 Organic forms (selenomethionine) preferred
Dosage
Typical range
100-200mcg daily
Timing
With meals
With food
Yes
Dose Tiers
RDA / DV
55 mcg
Moderate
100-200 mcg
Optimal
100-200 mcg selenomethionine
Upper Limit
400 mcg
Duration
Ongoing for thyroid support
Special Populations
Hashimoto's, hypothyroid, those on iodine
Research & Studies
Landmark clinical studies on Selenium. Each title links to a plain-English breakdown — what the study shows, what its limitations are, and how to read around them.
- Effect of selenium and vitamin E on risk of prostate cancer and other cancers: the Selenium and Vitamin E Cancer Prevention Trial (SELECT)
Large primary-prevention RCT (n=35,533) found selenium 200µg/day did not prevent prostate cancer — and later follow-up raised concerns about increased type 2 diabetes risk at supplemental doses in selenium-replete populations.
- The importance of selenium to human health
Landmark review of selenium's role in thyroid hormone metabolism, immune function, and antioxidant defense — with clinical relevance for deficient populations but not universally beneficial supplementation.
Browse all curated studies →
Mechanism of Action
- • Required for deiodinase enzymes
- • Converts T4 to active T3
- • Protects thyroid from oxidative damage
- • May reduce thyroid antibodies
Evidence Quality
Evidence Grade A
Well-established for thyroid function and protection
Safety & Contraindications
Serious Warnings
- • Toxicity above 400mcg chronically
- • Narrow therapeutic window
Contraindications
- • Excessive supplementation
Common Side Effects
- • Garlic breath (high dose)
- • GI upset
Pregnancy & Breastfeeding
Consult healthcare provider
Liver & Kidney Notes
Safe at normal doses
Interactions
💊 Medications
- • May affect thyroid medication needs
🧪 Supplements
- • Essential partner to iodine
- • Works with zinc
🍽️ Food & Alcohol
- • With food
Stacking & Synergies
Pairs Well With
Avoid Combining With
Excessive doses
Best Goal Synergies
T4 to T3 conversionThyroid protection
Buying Guide
What to Look For
- • Selenomethionine form
- • 200mcg or less daily
Standardization Markers
Mcg seleniumForm (selenomethionine best)
Adulteration risk
Low
Practical Notes
- • Don't exceed 400mcg daily
- • Brazil nuts are rich source
- • Important for thyroid
- • Critical for T4→T3 conversion
- • Protects thyroid when using iodine
- • Don't exceed 200mcg daily
- • SELECT trial caution - don't exceed 200mcg
- • 1-2 Brazil nuts provides selenium
- • Moderate doses only
Tags
immunemineralthyroidantioxidanthashimoto'sprostatecontroversial
Top Products with Selenium
Highest-scored catalog products containing Selenium, ranked by our scoring engine.
SeleniumThorne96
Thyroid Health Complex (formerly Thyrocsin)Thorne90
Advanced NutrientsThorne88
Basic Nutrients 2/DayThorne88
Related Guides
In-depth guides covering Selenium — protocols, comparisons, and use cases.
More in Mineral
Other ingredients in the Mineral category.
Boron
Trace mineral supporting bone health, cognitive function, and hormone metabolism. May support testosterone in deficient states.
Calcium
Essential mineral for bone health, muscle function, nerve signaling, and blood clotting.
Calcium Carbonate
Common, economical calcium form with highest elemental calcium percentage. Requires stomach acid for absorption.
Calcium Citrate
Well-absorbed calcium form that doesn't require stomach acid. Better for those on acid-reducing medications.
Chloride
Essential electrolyte mineral that works with sodium and potassium to maintain fluid balance, nerve transmission, and stomach acid production.
Chromium Picolinate
Trace mineral for insulin sensitivity and blood sugar regulation. Popular for carb cravings.
Last reviewed: September 2026 by the Formulate Research Team. Sources cited above; methodology and scoring criteria published here.
Cite this page
Formulate Research Team. (2026, September). Selenium — Evidence-Based Supplement Guide. Formulate Supplement Encyclopedia. https://app.formulate-health.app/learning/supplements/selenium
Educational content based on published research and our scoring methodology. Not medical advice — consult a qualified healthcare provider before starting, stopping, or changing supplements, especially if you take medications, are pregnant, or have a medical condition.