VitaminWell-studiedMineral

Selenium

Half-life

~102 days

What is Selenium?

Essential trace mineral and potent antioxidant cofactor. Important for thyroid hormone conversion.

How Selenium works

Incorporated into selenoproteins including glutathione peroxidase (GPx), thioredoxin reductase (TrxR), and iodothyronine deiodinase (converts T4→active T3 in the thyroid).

Benefits & uses

Thyroid support
Antioxidant defense
Immune support

Common uses: Thyroid function (T4→T3 conversion), antioxidant defense, immune support.

Longevity

Selenium dosage

Typical dose: 100–200 mcg/day selenomethionine or sodium selenite with food. Do not exceed 400 mcg/day (UL). Test serum selenium before supplementing.

Selenium half-life

~102 days (tissue stores; varies by form)

Selenium side effects

Selenium toxicity (selenosis) at doses >400 mcg/day: garlic breath, hair loss, GI issues.

Selenosis at >400 mcg/day: garlic/metallic breath, hair and nail brittleness
GI distress
Peripheral neuropathy with chronic excess
Never exceed 400 mcg/day — therapeutic window is narrow
Well tolerated at normal doses

Warnings & monitoring

Narrow safe range — avoid chronic doses above ~400 mcg (selenosis)

Track Selenium in Protokol.

Log doses, model half-lives, check interactions, and line it all up against your bloodwork. Free on iPhone and Android.