Selenium
A trace mineral where the gap between not enough and too much is genuinely narrow.
Selenium is a component of enzymes that protect cells from oxidative damage and convert thyroid hormone into its active form. Selenomethionine, the organic form found in Brazil nuts and used in most trials, is absorbed at roughly 90% and retained well in tissue; sodium selenite, the inorganic form, is absorbed but not held onto as efficiently. The upper limit isn't generous relative to typical supplement doses, particularly for anyone eating Brazil nuts regularly alongside a supplement, since a handful can already provide several times the daily reference intake on its own.
Reference values
Daily reference values from official nutrition authorities. These are population reference figures, not personal recommendations.
| Group | RDA | Upper limit | Source |
|---|---|---|---|
| Women, 19+ | 60 mcg | 300 mcg | UK SACN DRVs (1991, confirmed in 2013 update) -- women 60 mcg/day; EFSA UL 300 mcg/day (2018) |
| Men, 19+ | 75 mcg | 300 mcg | UK SACN DRVs (1991, confirmed in 2013 update) -- men 75 mcg/day; EFSA UL 300 mcg/day (2018) |
Forms and bioavailability
Not all forms are absorbed equally. The form on your supplement label affects how much your body can actually use.
| Form | Absorption | With food | Timing | Evidence |
|---|---|---|---|---|
| Selenomethionine | Higher | With food | Either | Strong |
| Selenium yeast (selenised yeast) | Higher | With food | Either | Likely |
| Sodium selenite (inorganic) | Lower | With food | Either | Strong |
How it pairs with other supplements
Works well with
Selenium and iodine work together in thyroid hormone synthesis: selenium-dependent deiodinases convert T4 to active T3, and selenoperoxidase protects the thyroid gland from oxidative damage during hormone synthesis. Supplementing iodine without adequate selenium in iodine-deficient populations may worsen autoimmune thyroiditis.
Stack Almanac totals your selenium across supplements and flags your running total against the upper limit, and factors in the iodine connection when you're taking both for thyroid support.
Track your Selenium in Stack Almanac
Last reviewed: 2026-07-08. Reference values are adult-general RDAs from UK. Individual needs may vary. This page is for informational purposes only and is not a substitute for professional medical advice.