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: 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.
4,858 natural health products with an active licence 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.
