Selenium (Serum)
Other marker
Selenium
Selenium (Serum)
The serum level of selenium, an essential trace element and cofactor for antioxidant selenoenzymes (glutathione peroxidases) and for the deiodinases that convert thyroid hormone T4 to active T3. This entry tracks the measured blood level, distinct from selenium taken as a supplement.
PED Notes
Selenium is frequently recommended as a supplement on this platform for thyroid support and antioxidant defence, so athletes who follow that advice may want to confirm they are in range rather than over-supplementing. The therapeutic window is narrow: enough selenium supports T4-to-T3 conversion and glutathione peroxidase activity, but chronic excess (selenosis) causes hair and nail loss, garlic breath, and neuropathy. High-dose 'thyroid' or 'antioxidant' stacks can push intake into the toxic range.
When high
When high (>150 mcg/L, moving toward selenosis):
- Usually from over-supplementation, sometimes from stacking multiple products (thyroid support, antioxidant blends, Brazil nuts); audit total intake
- Chronic excess causes brittle hair and nails, hair loss, a garlic-like breath odour, gastrointestinal upset, and, in severe cases, peripheral neuropathy
- Action: stop selenium supplements, reduce Brazil-nut intake (very selenium-dense), and recheck; levels fall over weeks once intake normalises
When low
When low (<70 mcg/L, deficiency):
Supplements:
- Selenium (selenomethionine) -- 100-200mcg/day; supports glutathione peroxidase and thyroid deiodinase activity; do not exceed ~400mcg/day total from all sources
- Brazil nuts -- 1-2 per day is a food-based option (each provides roughly 70-90mcg), but variable content makes precise dosing hard
Relevance:
- Adequate selenium supports conversion of T4 to active T3; low selenium can blunt thyroid function and is worth correcting in athletes with borderline thyroid labs
- Selenium also supports antioxidant defence, complementing the liver-support and cardiovascular strategies used by enhanced athletes
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Frequently Asked Questions
Reference Ranges
Standard Range