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
Ongoing
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.
Evidence
Evidence Strength
Strong (human RCTs / meta-analyses)
Caveats
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.
Usage
Commonly Referenced Starting Amount
55 mcg/day
Commonly Referenced Amount
100–200 mcg/day is the range used in most selenium trials
Referenced Upper Limit
400 mcg/day is the IOM upper limit, set by selenosis (hair and nail loss, neuropathy) — this is a narrow window between adequate and excessive
Onset
4–8 weeks (thyroid)
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.
Disclaimer
This information is for educational purposes only and is not medical advice. It is not intended to diagnose, treat, cure, or prevent any disease. Consult a qualified healthcare provider before starting any new supplement, especially if you are pregnant, nursing, taking medication, or managing a health condition.
Rayman MP (2012). The Lancet. Review (selenium and human health). PMID: 22381456.
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