Selenium: The Complete Guide
200 mcg once, under the 400 mcg ceiling, and not on top of Brazil nuts
Selenium is required for glutathione enzymes and thyroid hormone conversion. The adult RDA is 55 mcg; the upper limit is 400 mcg a day from all sources. NOW’s 200 mcg L-selenomethionine is the Amazon capsule. One capsule plus a high-selenium multi plus Brazil nuts is how people overshoot. This is not a cancer protocol.
Health Disclaimer
This content is for general informational and educational purposes only. It is not medical advice, diagnosis, or treatment. Consult a qualified healthcare provider before starting any supplement, peptide, or health protocol. Read our full health disclaimer.
Frequency
One 200 mcg capsule, if diet is low
Duration
Ongoing only if you are not also eating nuts and a multi
Level
Beginner
Key Takeaways
- 1200 mcg is above the RDA and still under the 400 mcg UL — until food is counted
- 2One capsule, not two
- 3Brazil nuts can match or beat a capsule; do not stack both daily
- 4Skip if your multi already has 200 mcg
Who this is for
- ·People whose diet has little seafood and no Brazil nuts
- ·Anyone about to double a 200 mcg capsule
- ·Readers of the NAC guide who noticed selenium on the NOW label
The Number
Strong EvidenceRDA is 55 mcg for adults. UL is 400 mcg from food plus supplements. NOW’s bottle is 200 mcg L-selenomethionine. That is a high supplement dose, not a starter you double.
NOW NAC also includes selenium. Read both labels before you add this capsule.
Nuts and Multis
Moderate EvidenceA single Brazil nut can rival 200 mcg, and the next nut is not a controlled dose. Pick the nuts or the bottle. If a multivitamin already lists 200 mcg, this SKU is redundant.
Skip
Moderate EvidenceTwo capsules ‘for antioxidant.’ Cancer-cure marketing. Stacking yeast selenium on selenomethionine. Thyroid disease is a clinician conversation, not a second pill.
As an Amazon Associate, Reo Tuku Iho Limited earns from qualifying purchases through Amazon links on this site. Full disclosure
For educational purposes only. Not medical advice. Read our health disclaimer.
Sources
Key references cited in this guide. Links open the original publication or abstract.
- Selenium — Fact Sheet for Health ProfessionalsNIH Office of Dietary Supplements, 2024
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