Mineral
Selenium
Also known as: Selenium glycinate
Essential trace mineral for glutathione peroxidase activity, thyroid function, and optimal immune response to viral infections.
Last reviewed June 2026 · Evidence graded from peer-reviewed research, not editorial opinion. Educational only — not medical advice.
Every Selenium product we have scored
| # | Product | Score | Per serving |
|---|---|---|---|
| 1 | Thorne Selenium | 96 A | $0.23 |
| 2 | Pure Encapsulations Selenium (citrate) | 94 A | $0.22 |
| 3 | Pure Encapsulations Selenium (selenomethionine) | 94 A | $0.24 |
| 4 | Nutricost Selenium Capsules | 94 A | $0.06 |
| 5 | Life Extension Se-Methyl L-Selenocysteine | 94 A | $0.09 |
| 6 | Natural Factors SelenoExcell Selenium | 92 A | $0.15 |
| 7 | Life Extension Super Selenium Complex & Vitamin E | 91 A | $0.10 |
| 8 | Thorne Thyroid Health Complex | 90 A | $0.33 |
| 9 | NOW Foods NAC | 89 A | $0.12 |
| 10 | MegaFood Skin, Nails & Hair 2 | 89 A | $0.87 |
| 11 | Thorne Advanced Nutrients | 88 A | $2.40 |
| 12 | Thorne Basic Nutrients 2/Day | 88 A | $0.60 |
Scored on dose accuracy, form, label transparency and third-party testing. Per-serving cost is list price divided by servings per container. No brand pays to be listed or ranked.
Common questions
How much Selenium should I take?
The typical range is 100-200mcg daily. Ongoing for thyroid support
When should I take Selenium?
With meals. Yes.
Which form of Selenium is best?
Selenomethionine — Best absorbed, incorporated into proteins. Other forms in the catalog: Selenium yeast, Sodium selenite, Brazil nuts.
Is Selenium safe?
Commonly reported: Garlic breath (high dose), GI upset. Serious warnings: Toxicity above 400mcg chronically, Narrow therapeutic window. Safe at normal doses
Which Selenium supplement scores highest?
Thorne Selenium, at 96/100. Scored on dose accuracy, form, label transparency and third-party testing — no brand pays to be listed or ranked.
Daily target & upper limit
55 mcg / day · UL 400 mcgSelenium has an established daily reference intake. See best forms, label synonyms, upper-limit warnings, and top-scoring supplements:
Selenium dosage reference →Primary uses
- Antioxidant enzyme support
- Thyroid function
- Viral immunity
- Selenoprotein production
- T4 to T3 conversion
- Thyroid protection
- Autoimmune thyroid (Hashimoto's)
- Prostate health
- Prostate cancer (controversial)
What systematic reviews concluded
Outcomes that systematic reviews of Selenium reached a verdict on: 9 with a benefit, 6 with no effect, 1 with harm reported, 3 unclear. Each is quoted from a review and linked to it on PubMed. How these were read.
Reviews found a benefit (9)
“dietary selenium significantly reduced HOMA-β (Homeostasis Model Assessment-Beta; p < 0.0001), triglycerides (p = 0.02), high-sensitivity C-reactive protein (p < 0.00001), and plasma malondialdehyde (p < 0.00001), while increasing total antioxidant capacity (p = 0.04)” PMID 41738711
“malondialdehyde (MDA; SMD -1.16 [CI -2.29 to -0.02]; 3 cohorts; 248 participants; I2 = 85%) decreased in patients with and without THRT” PMID 38243784 · 2 reviews
“increasing total antioxidant capacity (p = 0.04)” PMID 41738711
“dietary selenium significantly reduced HOMA-β (Homeostasis Model Assessment-Beta; p < 0.0001)” PMID 41738711
“but decreased risk for congenital heart defects (n = 1807), neural tube defects (max n = 12,188), and orofacial clefts (max n = 1155)” PMID 41683301
“Se supplementation help reduce TPOAb and TSH levels in HT patients, leading to improvements in well-being or mood” PMID 40898469 · 3 reviews
and 3 more.
Reviews found no effect (6)
“selenium had no significant effect on fasting plasma glucose, insulin levels, HOMA-IR (Homeostasis Model Assessment of Insulin Resistance), total cholesterol, low-density lipoprotein cholesterol, high-density lipoprotein cholesterol, very low-density lipoprotein cholesterol, nitric oxide, plasma glutathione, weight change, and body mass index change (all p > 0.05)” PMID 41738711
“it does not significantly affect total cholesterol, triglycerides, low density lipoprotein cholesterol, or high density lipoprotein cholesterol levels” PMID 41073938 · 2 reviews
“weight change, and body mass index change (all p > 0.05)” PMID 41738711
“Selenium exposure did not affect the risk of all/any congenital anomalies (n = 20,815), abdominal (n = 89,273) and limb anomalies (n = 551,547), chromosomal anomalies (n = 1242), or fetal alcohol syndrome (n = 41)” PMID 41683301
“No significant changes were observed in fT4, T4, fT3, T3, TGAb, thyroid volume, interleukin (IL)-2, and IL-10” PMID 38243784
“Adverse effects were comparable between the intervention and control groups (OR 0.89 [CI 0.46 to 1.75]; 16 cohorts; 1339 participants; I2 = 0%)” PMID 38243784
Harm reported (1)
“Higher concentrations of Se were associated with increased risk for urinary tract anomalies (n = 2150)” PMID 41683301
Not enough to say: fasting blood glucose; triglycerides; inflammatory markers and joint symptoms (ra: esr, crp, stiffness, swelling).
1 finding from reviews in specific patient groups (such as cancer, pregnancy or surgery) is not shown here.
How it works
- Required for deiodinase enzymes
- Converts T4 to active T3
- Protects thyroid from oxidative damage
- May reduce thyroid antibodies
Dosage
- Typical range
- 100-200mcg daily
- Timing
- With meals
- With food
- Yes
- Duration
- Ongoing for thyroid support
- Special populations
- Hashimoto's, hypothyroid, those on iodine
Forms
- Selenomethionine
- Selenium yeast
- Sodium selenite
- Brazil nuts
Safety
Common side effects
- Garlic breath (high dose)
- GI upset
Contraindications
- Excessive supplementation
Products containing Selenium
Top-scoring supplements in our catalog that list Selenium on the label. Each product is graded on Formulate's ingredient-level rubric — dose accuracy, form, transparency, and third-party testing.
Known interactions
Evidence notes
Well-established for thyroid function and protection
Grade A: Multiple well-designed human trials support the main claims.
Cited research for Selenium
Clinical studies referenced across Formulate guides that mention selenium. Each links to the full study page with PubMed source + the guides that cite it.
Related in Mineral
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Medical disclaimer. This page is educational and does not replace advice from a qualified healthcare provider. Individual needs and risks vary — consult a professional before starting, stopping, or combining supplements, especially if you are pregnant or nursing, taking medication, or managing a health condition.