Selenium (Thyroid Support)

Essential trace mineral crucial for thyroid hormone metabolism, antioxidant protection, and optimal thyroid gland function and health

Scientific nameSelenium FormulaSe Molecular weight78.96 g/mol CAS7782-49-2

85 absorption score

8 safety / 10

15 USD per month

100 elemental selenium %

5 documented interactions

Check it against something

Evidence level A

Selenium (Thyroid Support) with:

94 out of 100

Works better together Compatible. Timing differs, so follow each supplement's own window.

Check it against your whole stack →

What it does

mechanism and evidence for each claim

Essential thyroid hormone metabolism

Critical for proper conversion and metabolism of thyroid hormones

Required for deiodinase enzymes that convert T4 to active T3 Evidence A-grade 2-8 weeks

Thyroid gland protection and health

Protects thyroid gland from oxidative damage and inflammation

Selenoproteins provide antioxidant protection to thyroid tissue Evidence A-grade 4-12 weeks

Immune system support and regulation

Supports healthy immune function and autoimmune balance

Essential for immune cell function and inflammatory response regulation Evidence A-grade 2-8 weeks

Powerful antioxidant and cellular protection

Provides exceptional antioxidant protection against free radicals

Component of glutathione peroxidase and other antioxidant enzymes Evidence A-grade 1-4 weeks

Autoimmune thyroid condition support

May help reduce thyroid antibodies in autoimmune conditions

Reduces thyroid tissue inflammation and oxidative stress Evidence B-grade 8-16 weeks

Others take these for the same thing

Same goal, different mechanism — check any of them against this one

Melatonin Sleep support & circadian rhythm 0.5-3mg A 50% Ashwagandha Stress management & energy 300-600mg A 75% Vitamin B12 (Cyanocobalamin) Energy & nerve support 250-1000 mcg A 70% Coenzyme Q10 (CoQ10) Heart health & cellular energy 100-200mg A 10% Phosphorus Bone health & energy metabolism 700-1250mg A 80% Vitamin B3 (Niacinamide) Energy & skin health (no flush) 100-1000 mg A 88%

Every pair we checked

12 combinations scored by the engine

Selenium (Thyroid Support) + Vitamin D3 Very high vitamin C may reduce selenium absorption Needs attention 70

Selenium (Thyroid Support) + Vitamin C (Ascorbic Acid) Very high vitamin C may reduce selenium absorption Needs attention 70

Selenium (Thyroid Support) + Caffeine No documented interaction either way No known interaction 70

Selenium (Thyroid Support) + Creatine Monohydrate No documented interaction either way No known interaction 70

Selenium (Thyroid Support) + Calcium Carbonate No documented interaction either way No known interaction 70

Selenium (Thyroid Support) + Whey Protein No documented interaction either way No known interaction 70

Selenium (Thyroid Support) + Lactase No documented interaction either way No known interaction 70

Selenium (Thyroid Support) + Bovine Collagen No documented interaction either way No known interaction 70

Selenium (Thyroid Support) + DHA No documented interaction either way No known interaction 70

Selenium (Thyroid Support) + Turmeric No documented interaction either way No known interaction 70

Selenium (Thyroid Support) + Zinc Gluconate Improved thyroid hormone synthesis and immune function Works better together 86

Selenium (Thyroid Support) + Iodine (Thyroid Support) Essential synergy for complete thyroid function Works better together 94

Dosage

With food

Daily100-200mcg

Thyroid support100-200mcg daily

Autoimmune thyroid200mcg daily

Antioxidant protection100-200mcg daily

Immune support100-200mcg daily

Upper limit 400 mcg NIH ODS

When to expect it

First Effects1-4 weeks for initial antioxidant and immune improvements

Peak Benefits6-12 weeks for sustained thyroid and protective benefits

Deficiency DevelopmentCommon in areas with selenium-poor soil

Toxicity OnsetRisk increases with doses above 400mcg daily

How to measure it

$80-150

MarkerSerum selenium, selenoprotein P, thyroid function tests, glutathione peroxidase activity

OptimalSelenium 70-150 ng/ml, adequate selenoprotein P levels

Deficient belowSelenium <70 ng/ml, low selenoprotein P

FrequencyEvery 6-12 months for selenium status, every 3-6 months for thyroid function

What people actually reported to the FDA

CAERS, 63 reports naming it as the suspect

Most reported effects

Nausea 8

Dizziness 7

Fatigue 6

Vomiting 6

Pain 5

Named as the suspect 63 reports of 151 that mention it at all

Serious outcome 77% hospitalisation, emergency room or worse

Other Serious or Important Medical Event43

Visited a Health Care Provider27

Hospitalization23

Reports are voluntary and unverified — they record what someone experienced while taking something, not what the compound caused. Counts skew towards products people take a lot of, and a serious outcome is more likely to be reported than a mild one, so these are not rates. How we filter them →

What actually reaches you

The label counts the carrier, your body does not

Elemental selenium 100% of 78.96 g/mol

Absorption Very high 85 of 100 · best absorbed form of this compound

Delivered daily 0.1 mg

Cost per 1 mg delivered $3.92 comparative — uses the absorption score, not a measured percentage

A 500 mg capsule of Selenium (Thyroid Support) contains 500 mg of selenium. How much of that crosses into your blood is not measured for this form — the absorption score ranks it against other forms, it is not a share of the dose. How this is calculated →

Works better with

3 documented

Iodine

Essential synergy for complete thyroid function

Selenium protects thyroid during iodine-dependent hormone synthesis · level A

Vitamin E

Enhanced antioxidant protection and cellular defense

Both provide complementary antioxidant protection systems · level A

Zinc

Improved thyroid hormone synthesis and immune function

Both essential for thyroid function and immune system health · level B

What not to take with Selenium (Thyroid Support)

2 documented

Mercury Heavy Metals

Heavy metals can deplete selenium and oppose its benefits

Mercury binds selenium reducing bioavailability · high significance

Vitamin C High Doses

Very high vitamin C may reduce selenium absorption

Chemical interaction affecting selenium bioavailability · mild significance

Medication interactions

Discuss these with a pharmacist before combining

thyroid-medications Minor

May enhance thyroid medication effectiveness

What to do: Monitor thyroid function with selenium supplementation

immunosuppressive-drugs Minor

May affect immune suppressing medication effectiveness

What to do: Monitor immune function

Available forms

bioavailability compared

Ranks 2 of 2 among selenium forms. Selenium (Selenomethionine) absorbs better — 95%. Compare all forms →

Selenomethionine (Organic Form with Best Absorption) 85

Selenomethionine (Organic Form with Best Absorption): Essential thyroid function, Antioxidant protection, Immune support, Well absorbed

Food sources

before you supplement

Brazil nuts 70-100mcg per nut · 90

Fish and seafood 30-60mcg per 100g · 80

Meat and poultry 10-40mcg per 100g · 75

Whole grains 5-40mcg per 100g (varies by soil) · 70

Too little

deficiency signs

Selenium deficiency symptoms:
Impaired thyroid hormone conversion (T4 to T3)
Increased thyroid gland vulnerability to damage
Compromised immune function and increased infections
Reduced antioxidant protection and increased oxidative stress
Muscle weakness and cardiomyopathy in severe cases
Increased risk of autoimmune thyroid conditions

Too much

toxicity signs

Selenium toxicity (selenosis) symptoms:
Hair loss and nail brittleness
Garlic breath odor and metallic taste
Nausea, vomiting, and fatigue
Skin rash and nervous system symptoms
Occurs with doses above 400mcg daily long-term

Who benefits most

thyroid-function-optimization

Essential thyroid hormone metabolism and gland protection

100-200mcg daily

autoimmune-thyroid-support

Reduction of thyroid inflammation and antibody levels

200mcg daily

antioxidant-cellular-protection

Powerful antioxidant defense and cellular protection

100-200mcg daily

immune-system-support

Immune function enhancement and regulation

100-200mcg daily

selenium-deficient-regions

Essential supplementation in areas with low soil selenium

100-200mcg daily

Where to buy it

compare forms first

Look for Selenium (Thyroid Support) at 100-200mcg per serving. The form that matters here is Selenomethionine (Organic Form with Best Absorption).

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What else affects it

Beyond other supplements

Mercury heavy metals

Heavy metals can deplete selenium and oppose its benefits

Mercury binds selenium reducing bioavailability

How it works

Essential cofactor for type I, II, and III deiodinase enzymes converting T4 to T3
Component of glutathione peroxidase providing antioxidant protection to thyroid
Required for selenoprotein P synthesis protecting against oxidative stress
Essential for thioredoxin reductase supporting cellular redox balance
Supports immune cell function and inflammatory response regulation
Protects thyroid gland from hydrogen peroxide damage during hormone synthesis

Key findings

what the evidence supports

Extensive evidence for essential thyroid hormone metabolism
Strong research on antioxidant protection and immune function
Good evidence for autoimmune thyroid condition support
Critical to avoid both deficiency and excess intake

Sources: NIH Examine.com · data reviewed 2026-08-02

Compiled by Denis, who maintains this database and holds no medical qualification — every figure here is sourced or derived, never asserted. How we calculate it →

Common questions

What are the benefits of Selenium (Thyroid Support)?

Documented effects: Essential thyroid hormone metabolism; Thyroid gland protection and health; Immune system support and regulation; Powerful antioxidant and cellular protection. Critical for proper conversion and metabolism of thyroid hormones

How much Selenium (Thyroid Support) should you take per day?

The common daily range is 100-200mcg. By goal — thyroid support: 100-200mcg daily; autoimmune thyroid: 200mcg daily; antioxidant protection: 100-200mcg daily; immune support: 100-200mcg daily.

When is the best time to take Selenium (Thyroid Support)?

With food. First effects are typically reported within 1-4 weeks for initial antioxidant and immune improvements.

What are the side effects of Selenium (Thyroid Support)?

At excessive doses: Selenium toxicity (selenosis) symptoms:, Hair loss and nail brittleness, Garlic breath odor and metallic taste, Nausea, vomiting, and fatigue, Skin rash and nervous system symptoms. Safety rating at normal doses is 8 out of 10.

What should you not take with Selenium (Thyroid Support)?

Separate it from Mercury Heavy Metals, Vitamin C High Doses by two to four hours. Heavy metals can deplete selenium and oppose its benefits

Does Selenium (Thyroid Support) interact with medications?

Documented interactions with thyroid-medications, immunosuppressive-drugs. Discuss these with a pharmacist before combining.

How much Selenium (Thyroid Support) is too much?

The tolerable upper intake level is 400 mcg per day for adults, per NIH ODS. Above that, the risk of adverse effects rises: Selenium toxicity (selenosis) symptoms:, Hair loss and nail brittleness, Garlic breath odor and metallic taste.

How do you know if you need Selenium (Thyroid Support)?

The marker is Serum selenium, selenoprotein P, thyroid function tests, glutathione peroxidase activity, optimal range Selenium 70-150 ng/ml, adequate selenoprotein P levels. Common deficiency signs: Selenium deficiency symptoms:, Impaired thyroid hormone conversion (T4 to T3), Increased thyroid gland vulnerability to damage, Compromised immune function and increased infections.

Taken for

62 Energy & Metabolism

Vitamin B12 (Methylcobalamin) · Ashwagandha · Vitamin B12 (Cyanocobalamin)

27 Hormones

Melatonin · Vitamin B6 (Pyridoxine HCl) · Vitamin B6 (P5P)