Selenium Dosage Calculator

What is Selenium?

Selenium is incorporated as selenocysteine (the 21st amino acid) into 25 selenoproteins with essential biological functions: glutathione peroxidases (GPx1–4) neutralise lipid peroxides and H₂O₂; thioredoxin reductase (TrxR) regenerates thioredoxin for ribonucleotide reductase and Nrf2 activation; and iodothyronine deiodinases (DIO1–3) catalyse the conversion of T4 prohormone to active T3, making selenium a critical thyroid cofactor alongside iodine. Selenium deficiency — endemic in regions with selenium-poor soils (parts of China, New Zealand, sub-Saharan Africa, and inland Europe) — causes Keshan disease (dilated cardiomyopathy, primarily in children), Kashin-Beck disease (osteoarthropathy), and profound hypothyroidism even with adequate iodine. Subclinical deficiency presents as impaired antioxidant capacity, reduced T3 levels, impaired immune function, and male infertility (selenoproteins are essential for sperm motility and morphology). Serum selenium < 70 mcg/L is considered deficient. Consult your physician and request serum selenium measurement before supplementing, particularly if you have thyroid disease.

How to Take Selenium

**RDA:** 55 mcg/day (adults). **UL: 400 mcg/day** — the UL is critically important: selenium toxicity (selenosis) occurs at chronic intakes above 400 mcg/day and causes hair loss, nail brittleness, garlic breath (dimethylselenide exhalation), peripheral neuropathy, and GI distress. **Supplemental forms:** Selenomethionine (from yeast or synthetic) has the highest bioavailability (~90%) and is the preferred form for repletion and general supplementation. Sodium selenite and selenate are inorganic forms with lower bioavailability but extensively studied in cancer prevention trials. For thyroid support: 100–200 mcg/day selenomethionine. For antioxidant/immune support: 50–100 mcg/day. Do not combine with high-dose selenium supplements and selenium-containing multivitamins — total daily intake must stay below 400 mcg.

Timing Recommendations

Take with food to improve GI tolerability and absorption. No specific timing requirement. Consistent daily intake is more important than timing relative to exercise or meals. Co-administration with vitamin E enhances synergistic antioxidant activity (GPx relies on reduced glutathione; vitamin E protects cell membranes).

Potential Side Effects & Safety

Within RDA range (55–200 mcg/day): well tolerated with no established adverse effects. Above UL (> 400 mcg/day): selenosis — hair loss, nail brittleness, garlic-like breath odour, irritability, fatigue, peripheral neuropathy, and in severe cases, cirrhosis and pulmonary oedema. The SELECT trial found selenium supplementation at 200 mcg/day increased type 2 diabetes risk in men with already-high baseline selenium levels — emphasising the importance of baseline testing before supplementing.

Best Stacks with Selenium

Selenium + iodine is the essential thyroid duo. Selenium + zinc for male reproductive health (both are concentrated in testicular tissue and required for testosterone and sperm function). Selenium + NAC + vitamin E = comprehensive cellular antioxidant network.

Scientific References

All dosage recommendations are grounded in peer-reviewed research.

1. 1
   Selenium and human health

   The Lancet · 2012

2. 2
   Selenium status and thyroid disease: a systematic review

   Thyroid · 2020