Selenium

Also known as: Selenium glycinate

Grade A

💊 100-200mcg daily🎯 10 primary uses🔗 3 synergies⚠️ Review warnings

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 forms

Different chemical forms vary in absorption, side effects, and best use cases. Higher bioavailability scores indicate better absorption.

Selenomethionine

HIGH 100

Selenium 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 95

Methylated 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 85

Selenium-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 70

Inorganic 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)
Lippman SM, Klein EA, Goodman PJ, et al. · 2009 · JAMARCTPubMed ↗
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
Rayman MP · 2000 · LancetReviewPubMed ↗
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.

PubMed (RCTs) ↗Randomized trials PubMed (all) ↗Full literature Cochrane Reviews ↗Systematic reviews Examine.com ↗Research summaries

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

Iodine ↗Zinc ↗Vitamin E ↗

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

Top Products with Selenium

Highest-scored catalog products containing Selenium, ranked by our scoring engine.

Browse all Selenium products →

Related Guides

In-depth guides covering Selenium — protocols, comparisons, and use cases.

Best Multivitamin Over 50↗

More in Mineral

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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.

Browse all Mineral ingredients →

Last reviewed: June 2026 by the Formulate Research Team. Sources cited above; methodology and scoring criteria published here.

Cite this page

Formulate Research Team. (2026, June). 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.