Full profile
| Also known as | Selenomethionine |
|---|---|
| Best for | Not featured as a cognitive active — evaluated and graded out on a safety signal · Any legitimate use is confined to documented deficiency (rare in Canada/US) under clinical guidance |
| Evidence grade | Graded Out — Graded out — evaluated and not featured (failed replication or a safety signal) |
| Studied dose range | Not recommended as a cognitive supplement. For reference: RDA is 55 mcg/day and typical North American intake already meets it; the tolerable upper limit is just 400 mcg/day — one of the narrowest windows of any micronutrient. Cognition/prevention trials used ~200 mcg/day. |
| Time to effect | Not applicable — no reliable cognitive benefit demonstrated in replete adults. |
| Best form | For diagnosed deficiency only, selenomethionine is well absorbed; note that 1–2 Brazil nuts can exceed the RDA, underscoring how little supplemental headroom exists. |
| Food sources | Brazil nuts (very high — 1–2 can exceed the RDA), Seafood, Organ meats, Eggs, Whole grains |
Evidence, honestly graded
Graded out on a safety-and-null-evidence basis. Observational data link low selenium to cognitive decline, but randomized supplementation trials in replete older adults show no cognitive or dementia-prevention benefit (SELECT, Lippman 2009; PREADViSE, Kryscio 2017), while the gap between the RDA (55 mcg) and the upper limit (400 mcg) is dangerously narrow — chronic excess causes selenosis, and high supplemental intake carries a type-2-diabetes-risk signal. For a largely selenium-replete population, the risk/benefit does not support featuring it as a cognitive active.
See the full grading rubric — study type, replication, population match, and dose adequacy — in The Evidence Standard.
4,358 licensed natural health products in Health Canada's LNHPD list Selenium as a medicinal ingredient.
That makes Selenium a recognized, licensable medicinal ingredient in Canada — regulated by Health Canada's Natural and Non-prescription Health Products Directorate, which issues each licensed natural health product a Natural Product Number (NPN). Search the LNHPD to verify.
Side effects
- Selenosis with chronic excess: hair loss, brittle or lost nails, garlic breath, metallic taste, rash, GI upset, fatigue, irritability, peripheral neuropathy
- Possible increased type-2-diabetes risk at high supplemental intake
Who should avoid it or check first
- Already selenium-replete (most Canadian/US adults)
- High Brazil-nut intake
- On other selenium-containing supplements
- Pregnancy without documented need
Interactions
- Additive toxicity with other selenium sources and multivitamins
- Possible interaction with anticoagulants and with cisplatin and other chemotherapies
Use caution stacking with
What to look for on a label
- Documented here for transparency — not a featured cognitive active. The narrow 55 mcg RDA / 400 mcg upper-limit window and selenosis risk must be respected.
- North American diets are typically already selenium-sufficient; routine supplementation for cognition is not supported.
References
- Lippman SM, Klein EA, Goodman PJ, et al. (2009). JAMA, 301(1):39–51Selenium did not prevent cancer; null benefit.
- Kryscio RJ, Abner EL, Caban-Holt A, et al. (2017). JAMA Neurology, 74(5):567–573No dementia prevention from selenium and/or vitamin E.
- NIH Office of Dietary Supplements — Selenium fact sheet. States the 400 mcg/day upper limit and selenosis risk, and that clinical-trial evidence does not support selenium supplementation to reduce cognitive-decline or dementia risk. Authoritative government reference (ods.od.nih.gov/factsheets/Selenium-HealthProfessional).
Entries above without a linked identifier are either editorial summaries of a wider body of literature or references to a named authority (a regulator or government monograph) cited by name rather than by a single paper.
Grades and studied doses are our conservative reading of the human research, shown for education. They are not product claims, and a studied dose is not a recommended dose.
Revision history
Every change to this ingredient's evidence status, dated and explained. The full cross-library log lives at Evidence Updates.
- 2026-07-12Graded out
Published straight into Graded Out on a safety-and-null-evidence basis. Randomized trials in replete older adults show no cognitive or dementia-prevention benefit (SELECT, PREADViSE), and the window between adequate and excessive intake is narrow.
See how Selenium compares on grade, dose, and goal in the Evidence Explorer.
