Selenium
Research Reliability -
A trace mineral antioxidant that supports thyroid hormone production, immune function, and protection against oxidative damage.
Appetite
Mood
Sleep
Selenium
Description
Selenium is an essential trace element incorporated into selenoproteins, which are powerful antioxidant enzymes including glutathione peroxidase. It plays a critical role in thyroid hormone metabolism, converting T4 to the active T3 form, and is frequently depleted in individuals with thyroid dysfunction. Selenium also supports immune function, reduces inflammation, and may lower the risk of certain cancers with consistent, long-term intake. Soil depletion in many regions makes dietary selenium intake unreliable, making supplementation a prudent choice.
Effects
First weeks
no felt change
Weeks 4–8
thyroid antibody and function markers may improve on labs
Ongoing
antioxidant and thyroid support
How it Feels
Selenium is a lab supplement, not a felt one. Its value is in thyroid and antioxidant markers. The range between helpful and too much is narrow, so stick close to the standard dose.
Usage
Entry Dose
55mcg
Standard Dose
100–200mcg
Max Dose
400mcg
Onset
4–8 weeks (thyroid)
Combinations
Pairs well with
Synergistic
Vitamin E — synergistic antioxidant pair; selenium recycles vitamin E
Iodine — selenium is required to convert T4 to active T3 thyroid hormone
Zinc — thyroid and immune axis; both are essential for GPx enzyme systems
Avoid combining
Contraindicated
Excess selenium >400mcg/day — selenosis risk; hair loss, GI distress, neurological effects
Chemotherapy — antioxidant activity may interfere with treatment; consult oncologist
Biomarkers to Track
Subjective
(Daily)
Hair texture and shedding rate
Energy and thyroid symptoms
Mood stability score (1–10)
Objective
(Quarterly)
Serum selenium level
TSH and free T3/T4
Thyroid peroxidase antibodies
Helpful in small amounts but has a narrow safe window. Excess causes selenosis with hair loss and nail changes.
Anyone already using a multivitamin with selenium, to avoid stacking past the limit.
Taking multiple products that each contain selenium, and assuming more helps the thyroid.
Strong (human RCTs / meta-analyses)
The SELECT trial found supplementation in selenium-replete men did not reduce cancer risk and was linked to increased type 2 diabetes risk; do not supplement without evidence of deficiency.
Rayman MP (2012). The Lancet. Review (selenium and human health). PMID: 22381456.