Compound or practice · Supplement
Selenium
A trace mineral with a narrow safe window — correct a deficiency, don't chase antioxidant megadoses.
- Overall grade
- Grade C
- Last revised
- 2
- graded outcomes
- 0
- references listed
A structured monograph in Prometheus's bundled library. Its grades are the monograph's own reading of the evidence, not a peer-reviewed review.
1 at grade C · 1 at grade D — 2 graded rows
What is known
Each outcome with its grade (how strong the evidence is, A to D), the size of the effect where the entry records one, and how often studies agree.
- Autoimmune thyroiditis antibodiesEvidence grade C
Under care
Smallmixed
- Prostate cancer preventionEvidence grade D
SELECT null, possible harm
Trivialhigh
What is uncertain
Read off the same rows as above. Nothing here is added that the entry does not itself record.
- Thin evidence: Autoimmune thyroiditis antibodies (grade C); Prostate cancer prevention (grade D).
The evidence in words
What it is
Selenium is an essential trace mineral incorporated into selenoproteins, including antioxidant glutathione peroxidases and enzymes that activate thyroid hormone. Soil content varies widely, so intake tracks geography.
How it works
Selenoproteins recycle antioxidants and convert thyroxine (T4) to active T3, tying selenium to both oxidative defense and thyroid function.
What the evidence shows
Correcting genuine deficiency matters. But the flagship SELECT trial found no prostate-cancer benefit and hinted at harm, and high selenium intake is linked to type 2 diabetes risk and, in excess, toxicity (selenosis). There is modest evidence in autoimmune thyroiditis. This is a nutrient with a narrow therapeutic window — more is not better.
How to use it
A couple of Brazil nuts or a modest multivitamin dose covers requirements. Therapeutic use in thyroid disease belongs under a clinician; avoid standalone high-dose selenium.
Safety & interactions
Toxic in excess: hair and nail loss, GI and neurological effects. The gap between adequate and harmful is smaller than for most nutrients.
Bottom line
Get enough (a Brazil nut or two), avoid megadosing. The 'antioxidant prevents cancer' pitch failed in trials and high intakes carry real downsides.
How it is used
As the entry records it, from the studies it summarises. Not a recommendation for you — doses that suit a trial population may not suit you.
- Adequacy
- Modest dose or 1–2 Brazil nuts; avoid high-dose standalone.
Related reading
Entries that share this one's tags or conditions.
- Selenium for Autoimmune thyroiditis antibodiesEvidence grade C — Under careEvidence grade C
- Selenium for Prostate cancer preventionEvidence grade D — SELECT null, possible harmEvidence grade D
- Selenium: dosage and how to take itModest dose or 1–2 Brazil nuts; avoid high-dose standalone.Evidence grade C
- Selenium: side effects, safety & interactionsToxic in excess: hair and nail loss, GI and neurological effects. The gap between adequate and harmful is smaller than fEvidence grade C
Sources
This entry lists no references of its own.
Last revised . A grade is this entry's reading of the evidence, not medical advice.