What is the best form of selenium?
2 forms compared by what actually reaches your bloodstream. Absorption ranges from 85% to 95% — a difference that matters more than the milligrams on the label.
Ranked by absorption
Higher means more of the dose reaches youShort answer
Selenium (Selenomethionine) absorbs best — 95%.
Superior antioxidant & thyroid support. Typical dose 100-200 mcg, about $15 a month.
Which form for which goal
Best absorbed option that covers each useSame compound, different carrier — the goal changes which trade-off matters, not what the mineral does.
Every form side by side
| Form | Absorbed | Elemental | Cost / 1 mg delivered | Per month | Dose |
|---|---|---|---|---|---|
| Selenium (Selenomethionine) | 95% | 40.3% | $8.71 | $15 | 100-200 mcg |
| Selenium (Thyroid Support) | 85% | 100% | $3.92 | $15 | 100-200mcg |
What the label does not tell you
Selenium (Thyroid Support) looks like the strongest option on paper — it is 100% elemental selenium, the highest here. But its absorption score is 85 of 100, so a 500 mg capsule delivers about 425 mg to your bloodstream.
- Elemental percentage is how much of the compound is the mineral itself — the rest is the carrier the label counts as weight.
- Absorption is how much of that mineral crosses into your blood.
- Cost per 1 mg delivered multiplies both. It compares forms against each other, using the absorption score rather than a measured percentage — see how we derive it. Cheapest here: Selenium (Thyroid Support) at $3.92.
- Absorption is also dose-dependent: fractional uptake falls as the dose rises — roughly 65% at low intakes down to 11% at high ones.
What not to take with selenium
Same rules for every form — the interaction belongs to the mineral, not the carrierSeparating the two by two to four hours removes most of these: they compete for the same transporters in the gut, not in the bloodstream. Splitting the day is what solves a conflict — dropping one of the two is rarely necessary.
Medication interactions
May enhance anticoagulant effects · Monitor clotting times if using high doses
May enhance thyroid medication effectiveness · Monitor thyroid function with selenium supplementation
May affect immune suppressing medication effectiveness · Monitor immune function
May reduce chemotherapy toxicity · Consult oncologist about timing
May reduce statin-induced muscle damage · Consider selenium supplementation
Prescription medicine is your doctor's call, not ours — this is what the records list.
How much is too much
Upper limit for adults: 400 mcg a day, per NIH ODS.
Signs of overshooting it: selenosis: garlic breath and metallic taste, hair loss and brittle nails, skin rash and dermatitis, nervous system abnormalities.
63 reports to the FDA name selenium as the suspect product.
Most reported: nausea (8), dizziness (7), fatigue (6), vomiting (6). Serious outcomes: 77% of them.
Counted from FDA CAERS by parsing each report's product list, not by keyword — a report where the product was merely present does not count.
How to read this
- Absorption is the share of the dose that reaches your bloodstream — the number that decides whether the milligrams on the label mean anything.
- A cheaper form at half the absorption is not cheaper per unit delivered.
- Safety here reflects tolerance at normal doses, not toxicity risk.
- Evidence A means the form itself was studied, not just the parent compound.
Compiled by Denis, who maintains this database and holds no medical qualification. Absorption figures and cost-per-absorbed values are derived by published formulas from cited sources — see the arithmetic.
Common questions
What is the best form of selenium?
Selenium (Selenomethionine) — it scores 95 of 100 on absorption, the highest of the 2 forms here. Superior antioxidant & thyroid support. Typical dose 100-200 mcg.
Which form of selenium is worst absorbed?
Selenium (Thyroid Support) at 85%. It is usually the cheapest option, which is exactly why it ends up in budget products.
Is the expensive form of selenium worth it?
Compare per unit delivered, not per bottle. Selenium (Selenomethionine) costs $15 a month at 95% absorption, Selenium (Selenomethionine) costs $15 at 95%.
How much selenium should you take?
Doses differ by form: Selenium (Selenomethionine) 100-200 mcg; Selenium (Thyroid Support) 100-200mcg.