Evidence-based·Last reviewed May 31, 2026·How we grade evidence

Selenium Yeast

MineralSelenium sourceBest with a meal

Saccharomyces cerevisiae yeast grown in selenium-rich media, yielding 60–85% L-selenomethionine plus smaller fractions of other organic selenium species in a yeast-protein matrix. The form used in the NPC cancer-prevention trial. Comparable in bioavailability to pure L-selenomethionine in head-to-head studies. The optimistic NPC cancer-prevention signal did not replicate in the larger SELECT trial (which used pure L-selenomethionine), and a long-term NPC follow-up found increased type-2 diabetes risk at 200 µg/day in already-replete US adults.

Quick decision guide

May help most

Adults in genuinely low-selenium regions or with documented low plasma selenium who prefer an organic, multi-species selenium form. Use selenium yeast or pure L-selenomethionine — both are reasonable; selenium yeast is the historical default in many European products.

Common dosing range

100–200 µg/day. RDA is 55 µg/day; UL is 400 µg/day from all sources.

When to expect effects

Plasma selenium rises within 2–8 weeks; tissue stores take months.

Watch out for

Same narrow therapeutic window as all selenium: don't exceed 400 µg/day total. Long-term 200 µg/day in already-replete adults was associated with increased T2DM risk in the NPC follow-up.

Evidence snapshot

Correcting selenium deficiencyStrong

Cancer prevention (Se-replete adults)Low (refuted)

Thyroid antibodies (autoimmune thyroiditis)Moderate

T2DM risk signal at chronic high doseModerate concern

What is it

Selenium yeast is a form of dietary selenium produced by growing yeast (typically Saccharomyces cerevisiae) in selenium-enriched media. The yeast incorporates inorganic selenium into amino acids, predominantly selenomethionine, embedded in yeast proteins. This organic form of selenium is widely regarded as more bioavailable and retained than inorganic selenium salts like selenite.

Is it worth it for you?

Use this as a quick fit check, not a diagnosis.

Worth considering if…

You live in a low-selenium soil region (parts of UK/Europe, NE China) and don't eat Brazil nuts or much seafood

You have documented low plasma selenium and prefer an organic, multi-species form over pure selenomethionine

You're on long-term parenteral nutrition or have severe malabsorption

Your endocrinologist suggested a 3–6 month trial in Hashimoto's thyroiditis for antibody reduction

You want the form used in the original NPC trial (acknowledging the later null replication)

Probably skip if…

You eat Brazil nuts regularly (one nut delivers 70–90 µg — easily over the UL with a small handful)

You eat seafood multiple times per week — US/Canadian diets are typically already replete

You're hoping to prevent cancer — SELECT (pure selenomethionine) refuted the NPC signal at the same 200 µg/day dose

You already take a multivitamin or pure selenomethionine — stacking pushes total intake past the UL

You have type-2 diabetes risk factors and adequate selenium status — NPC follow-up showed increased T2DM at 200 µg/day in this population

Evidence at a glance

Goal	Effect	Best fit	Time
Correcting selenium deficiency Strong Evidence	Dose-dependent rise in plasma Se and selenoprotein-P; 100 µg/day adequate in many borderline-Se adults, 200 µg/day for catch-up in marginal status	Adults in low-Se regions, on parenteral nutrition, with severe malabsorption, or with documented low plasma selenium	Plasma Se rises within 2–8 weeks; tissue replenishment takes months
Hashimoto's thyroiditis — TPO antibody reduction Limited Evidence	~30–40% reduction in TPO antibody titres at 3 months in pooled analyses; thyroid function and symptom outcomes inconsistent	Adults with confirmed Hashimoto's (elevated TPO antibodies, clinical/biochemical findings) under endocrine care	3 months for antibody reduction
Chemotherapy / radiation mucositis (head & neck cancer) Mixed Evidence	No reduction in oral mucositis in the largest dedicated RCT	None established for this indication	Trial duration covered the full chemoradiation course
Cancer prevention Weak Evidence	Original NPC secondary signals not replicated by larger trials; SELECT primary cancer endpoint null	None established — the definitive larger trial refuted the cancer-prevention hypothesis	5+ year follow-up showed no benefit in SELECT

Correcting selenium deficiency

Strong Evidence

Effect: Dose-dependent rise in plasma Se and selenoprotein-P; 100 µg/day adequate in many borderline-Se adults, 200 µg/day for catch-up in marginal status
Best fit: Adults in low-Se regions, on parenteral nutrition, with severe malabsorption, or with documented low plasma selenium
Time: Plasma Se rises within 2–8 weeks; tissue replenishment takes months

Hashimoto's thyroiditis — TPO antibody reduction

Limited Evidence

Effect: ~30–40% reduction in TPO antibody titres at 3 months in pooled analyses; thyroid function and symptom outcomes inconsistent
Best fit: Adults with confirmed Hashimoto's (elevated TPO antibodies, clinical/biochemical findings) under endocrine care
Time: 3 months for antibody reduction

Chemotherapy / radiation mucositis (head & neck cancer)

Mixed Evidence

Effect: No reduction in oral mucositis in the largest dedicated RCT
Best fit: None established for this indication
Time: Trial duration covered the full chemoradiation course

Cancer prevention

Weak Evidence

Effect: Original NPC secondary signals not replicated by larger trials; SELECT primary cancer endpoint null
Best fit: None established — the definitive larger trial refuted the cancer-prevention hypothesis
Time: 5+ year follow-up showed no benefit in SELECT

Evidence for 4 uses

AI-assisted evidence assessment — talk to your doctor before relying on any single supplement.

Correcting selenium deficiency

Corrects deficiency

Strong Evidence

Selenium yeast reliably raises plasma selenium and selenoprotein-P in a dose-dependent way. The PRECISE pilot trial gave 501 elderly UK adults 100, 200, or 300 µg/day selenium-enriched yeast for 6 months and showed clean dose-response increases in plasma selenium. Selenium-yeast's predominant form (L-selenomethionine, 60–85%) is incorporated nonspecifically into body proteins in place of methionine, so it builds tissue selenium stores in addition to feeding selenoprotein synthesis. For genuine selenium deficiency — Keshan-disease-endemic regions, severe malabsorption, long-term parenteral nutrition — selenium yeast (or pure L-selenomethionine) is the right tool.

Effect size

Dose-dependent rise in plasma Se and selenoprotein-P; 100 µg/day adequate in many borderline-Se adults, 200 µg/day for catch-up in marginal status

Time to effect

Plasma Se rises within 2–8 weeks; tissue replenishment takes months

Best fit

Adults in low-Se regions, on parenteral nutrition, with severe malabsorption, or with documented low plasma selenium

Less likely

US/Canadian adults with mixed diets already at or above the RDA

Bottom line: Reliable for restoring selenium status when intake is genuinely low; not useful if you're already replete.

SourceStranges et al. (PRECISE pilot), 2014 — PMC — PLoS ONE Burk & Hill, 2015 — PMC — Annual Review of Nutrition NIH Office of Dietary Supplements — Selenium — Health Professional Fact Sheet

Hashimoto's thyroiditis — TPO antibody reduction

Disease adjunct

Limited Evidence

Multiple trials in autoimmune thyroiditis have used selenium-enriched yeast at 200 µg/day for 3–6 months and reported modest reductions in thyroid peroxidase (TPO) antibody titres. Whether antibody reduction translates to durable improvement in thyroid function, symptoms, or progression to overt hypothyroidism remains unclear. European endocrine guidelines do not routinely recommend selenium for Hashimoto's, but a 3–6 month time-limited trial of 200 µg/day under endocrine oversight is a reasonable consideration in symptomatic patients.

Effect size

~30–40% reduction in TPO antibody titres at 3 months in pooled analyses; thyroid function and symptom outcomes inconsistent

Time to effect

3 months for antibody reduction

Best fit

Adults with confirmed Hashimoto's (elevated TPO antibodies, clinical/biochemical findings) under endocrine care

Less likely

Healthy euthyroid adults with no autoimmunity

Bottom line: Reasonable short clinician-supervised trial in Hashimoto's; don't expect symptom relief by itself.

SourceNIH Office of Dietary Supplements — Selenium — Health Professional Fact Sheet

Chemotherapy / radiation mucositis (head & neck cancer)

Supplement benefit

Mixed Evidence

Karp 2013 randomised 140 patients with head-and-neck cancer to selenium yeast 200 µg/day or placebo during chemoradiation. The primary endpoint (oral mucositis incidence and severity) was not improved by selenium. This adds to a small body of trials testing Se-yeast in cancer-care settings; the picture is largely negative.

Effect size

No reduction in oral mucositis in the largest dedicated RCT

Time to effect

Trial duration covered the full chemoradiation course

Best fit

None established for this indication

Less likely

Cancer patients on chemoradiation who hope selenium will reduce mucositis

Bottom line: Don't use Se-yeast for radiation mucositis prevention — the best RCT was null.

SourceKarp et al., 2013 — Journal of Clinical Oncology

Cancer prevention

Supplement benefit

Weak Evidence

The NPC trial (Clark 1996) randomised 1,312 US adults with prior skin cancer to selenium-enriched yeast 200 µg/day or placebo. The primary endpoint (skin cancer recurrence) was negative; secondary endpoints showed apparent reductions in total cancer, prostate, lung, and colorectal cancer. These optimistic secondary signals drove enthusiasm for selenium supplementation for over a decade. The much larger SELECT trial (35,533 men, pure L-selenomethionine 200 µg/day) was stopped early for futility and definitively refuted the prostate-cancer-prevention hypothesis. Long-term NPC follow-up also showed increased type-2 diabetes risk. The cancer-prevention story for selenium yeast in Se-replete adults is over.

Effect size

Original NPC secondary signals not replicated by larger trials; SELECT primary cancer endpoint null

Time to effect

5+ year follow-up showed no benefit in SELECT

Best fit

None established — the definitive larger trial refuted the cancer-prevention hypothesis

Less likely

Men with high baseline selenium — possible signal of increased prostate cancer in SELECT subgroup re-analyses

Bottom line: Do not take selenium yeast to prevent cancer. The original optimistic signal didn't survive larger trials, and there's a T2DM safety signal.

Evidence is mixed

Original NPC trial (Clark 1996) had positive secondary endpoints for cancer prevention; larger and longer SELECT trial (using pure L-selenomethionine at the same dose) was definitively null and raised concern for harm. NPC follow-up by Stranges 2007 also added a T2DM safety signal.

SourceClark et al. (NPC trial), 1996 — JAMA· conflicting Stranges et al. (NPC follow-up), 2007 — Annals of Internal Medicine· conflicting Rayman, 2012 — The Lancet· conflicting

SourceClark et al. (NPC trial), 1996 — JAMA Stranges et al. (NPC follow-up), 2007 — Annals of Internal Medicine Rayman, 2012 — The Lancet

How it works

When consumed, selenium yeast delivers selenium primarily as selenomethionine, which is absorbed efficiently in the small intestine through the same pathways as the amino acid methionine. Selenomethionine is then either incorporated into body proteins (taking the place of methionine) or metabolized to release selenium for use in selenoproteins, which include glutathione peroxidases, thioredoxin reductases, and iodothyronine deiodinases (involved in thyroid hormone metabolism). Selenium yeast's incorporation into body proteins creates a tissue reserve of selenium that can be slowly released, leading to higher and more stable blood selenium levels compared with inorganic forms. This makes it particularly useful for correcting deficiency and maintaining selenium status.

How to take it

1. Typical dose

• 100–200 µg/day is the studied range; many products supply 200 µg per capsule • 55 µg/day meets the adult RDA • Stay at or below 400 µg/day total intake (food + supplements) — this is the UL • In Se-replete adults, daily intake above ~150 µg/day from supplements adds risk without clear benefit

2. Higher studied dose

200 µg/day was the dose used in the NPC trial and most cancer / Hashimoto's trials. PRECISE pilot tested 300 µg/day for 6 months without acute toxicity but with no clear clinical advantage. Do not chronically exceed 400 µg/day from all sources.

3. Timing

Take with a meal that contains some protein — selenomethionine is absorbed via methionine pathways and food helps consistency. Time-of-day does not materially affect efficacy.

4. With food

With food.

5. Split dosing

Single daily dose at 100–200 µg is appropriate. No advantage to splitting.

6. How long to try

3–6 months minimum to evaluate effect on thyroid antibodies; 4–8 weeks to see plasma-selenium changes. Avoid indefinite continuous use at 200 µg/day in already-replete adults given the T2DM signal — periodic plasma-Se rechecks and stopping when adequate is the safer pattern.

What to track

Plasma or serum selenium (target ~120–150 µg/L for selenoprotein saturation; values >150 µg/L do not add benefit and may add risk)

TPO antibodies if treating Hashimoto's — recheck at 3 months

Total Se intake from all sources — Brazil nuts, seafood, multivitamins, other Se products

Fasting glucose / HbA1c if on long-term 200 µg/day — NPC follow-up showed increased T2DM

Hair brittleness, nail changes, garlic-breath odour, GI upset — early selenosis signs (stop and seek advice)

Bottom line: 100–200 µg/day with food. Don't run it forever in already-replete adults; recheck plasma Se and stop when adequate.

4 commercial forms

Compare the main delivery options and what they’re best suited for.

Selenium-enriched yeast (Se-yeast)

Original NPC form

Saccharomyces cerevisiae grown in selenium-rich media. Selenium is incorporated into the yeast proteins predominantly as L-selenomethionine (60–85%) plus smaller fractions of selenocysteine, methylselenocysteine, and other organic species. Used in the original NPC cancer-prevention trial and the PRECISE pilot. Product-to-product variability is real — choose standardised brands that disclose the selenomethionine fraction (SelenoExcell, Sel-Plex, Cypress Selenium).

Comparable to pure L-selenomethionine in head-to-head studies; brand-to-brand variability.

Pure L-selenomethionine

Most-studied form

The single dominant selenium species (also dominant in Se-yeast and Brazil nuts). Used in the larger SELECT trial. Cleaner specification than yeast products; the all-L-isomer is the form found in human proteins.

Higher and more sustained rise in plasma Se than inorganic forms.

Sodium selenite (inorganic)

ICU / parenteral

Inorganic salt that feeds selenoprotein synthesis directly without building the tissue selenomethionine pool. Used in some European and ICU/parenteral nutrition products. Cheaper; raises plasma Se less per dose.

Lower retention than organic forms; doesn't build the tissue pool.

Sodium selenate (inorganic)

Less common

Inorganic salt similar in absorption to selenite. Mostly used in clinical-nutrition formulas.

Similar to selenite; less commonly on US/Canadian shelves.

Safety

Know the common side effects, key cautions, and who should avoid it.

Common side effects

garlic-like breath odourmetallic tastenauseamild GI upset

Serious risks

Selenosis from chronic intake above the 400 µg/day UL: hair loss, brittle or lost nails, GI distress, skin rash, fatigue, irritability, peripheral neuropathy. The 2008 US outbreak of 201 selenosis cases from a mislabeled liquid supplement (40,800 µg per recommended dose) showed many cases had persistent symptoms a year later.
SourceMacFarquhar et al., 2010 — Archives of Internal Medicine NIH Office of Dietary Supplements — Selenium — Health Professional Fact Sheet
Increased type-2 diabetes risk with long-term 200 µg/day selenium yeast in already-replete adults — observed in the NPC trial 8-year follow-up (HR 1.55, 95% CI 1.03–2.33). Avoid chronic high-dose use if you have T2DM risk factors and replete status.
SourceStranges et al. (NPC follow-up), 2007 — Annals of Internal Medicine
Acute selenium poisoning from gram-level overdose — rare but life-threatening: cardiovascular collapse, ARDS, multi-organ failure. Almost always from mislabeled or adulterated products.
SourceMacFarquhar et al., 2010 — Archives of Internal Medicine

Who should avoid it

People with high baseline plasma selenium (>120 µg/L) — supplementation adds risk without benefit and may increase cancer or diabetes risk in some subgroups.
SourceStranges et al. (NPC follow-up), 2007 — Annals of Internal Medicine Rayman, 2012 — The Lancet
Regular Brazil-nut eaters — one nut can supply 70–90 µg, easily exceeding the UL with a small handful per day.
SourceNIH Office of Dietary Supplements — Selenium — Health Professional Fact Sheet
Anyone already taking a multivitamin, pure L-selenomethionine, or another Se-containing supplement — check the combined daily dose first.
SourceNIH Office of Dietary Supplements — Selenium — Health Professional Fact Sheet
Children — pediatric ULs are much lower (60–280 µg/day depending on age); adult-strength capsules are easy to overdose.
SourceNIH Office of Dietary Supplements — Selenium — Health Professional Fact Sheet
People with yeast allergy or sensitivity — selenium yeast products contain inactivated yeast protein.

Pregnancy & breastfeeding

Pregnancy RDA is 60 µg/day and lactation 70 µg/day. Doses within the RDA are safe — severe selenium deficiency in pregnancy increases miscarriage risk. The 400 µg/day UL still applies; exceeding it during pregnancy hasn't been studied for birth-defect risk and is not recommended. Discuss with your obstetrician before supplementing beyond a standard prenatal.

SourceNIH Office of Dietary Supplements — Selenium — Health Professional Fact Sheet

Bottom line: Selenium has a narrow therapeutic window. Useful when truly low; harmful when already replete. Stay under 400 µg/day total and stop chronic 200 µg/day use in replete adults given the T2DM signal.

Interactions

vitamin E (high-dose, 400+ IU/day)Moderate

Co-supplementation with high-dose vitamin E was associated with increased prostate cancer risk in the SELECT trial. Avoid the combination if you're a man over 50.

SourceRayman, 2012 — The Lancet

cisplatin chemotherapyModerate

Cisplatin lowers serum selenium and may interact bidirectionally; selenium supplementation during cisplatin chemo should only be done with the oncologist's input.

SourceNIH Office of Dietary Supplements — Selenium — Health Professional Fact Sheet

other selenium-containing supplements (pure L-selenomethionine, multivitamins, Brazil-nut extracts)Moderate

Easy to exceed the 400 µg/day UL by stacking. Tally selenium from all sources before supplementing further.

SourceNIH Office of Dietary Supplements — Selenium — Health Professional Fact Sheet

barbiturates (phenobarbital)Minor

Barbiturates may increase selenium requirements via induced metabolism. Clinical relevance is limited; monitor plasma selenium if on long-term therapy.

SourceNIH Office of Dietary Supplements — Selenium — Health Professional Fact Sheet

warfarin / anticoagulantsMinor

Selenium may have additive antiplatelet activity at high doses; clinically meaningful interactions are uncommon. Monitor INR if combined long-term.

SourceNIH Office of Dietary Supplements — Selenium — Health Professional Fact Sheet

high-dose vitamin CMinor

Vitamin C can reduce selenite to elemental selenium in the gut, potentially lowering absorption of inorganic selenium forms. Less relevant for organic selenium yeast, but separate dosing by 1–2 hours is reasonable.

SourceNIH Office of Dietary Supplements — Selenium — Health Professional Fact Sheet

Food sources

Food	Amount	%DV
Brazil nuts	1 oz / 6–8 nuts (544 µg)	989%
Tuna, yellowfin, cooked	3 oz (92 µg)	167%
Halibut, cooked	3 oz (47 µg)	85%
Sardines, canned in oil	3 oz (45 µg)	82%
Shrimp, cooked	3 oz (42 µg)	76%
Beef steak, cooked	3 oz (33 µg)	60%
Cottage cheese, low-fat	1 cup (20 µg)	36%
Egg, hard-boiled	1 large (15 µg)	27%
Whole-wheat bread	1 slice (13 µg)	24%
Chicken breast, roasted	3 oz (22 µg)	40%
Brown rice, cooked	1 cup (19 µg)	35%
Oatmeal, cooked	1 cup (13 µg)	24%

Brazil nuts

Amount: 1 oz / 6–8 nuts (544 µg)
%DV: 989%

Tuna, yellowfin, cooked

Amount: 3 oz (92 µg)
%DV: 167%

Halibut, cooked

Amount: 3 oz (47 µg)
%DV: 85%

Sardines, canned in oil

Amount: 3 oz (45 µg)
%DV: 82%

Shrimp, cooked

Amount: 3 oz (42 µg)
%DV: 76%

Beef steak, cooked

Amount: 3 oz (33 µg)
%DV: 60%

Cottage cheese, low-fat

Amount: 1 cup (20 µg)
%DV: 36%

Egg, hard-boiled

Amount: 1 large (15 µg)
%DV: 27%

Whole-wheat bread

Amount: 1 slice (13 µg)
%DV: 24%

Chicken breast, roasted

Amount: 3 oz (22 µg)
%DV: 40%

Brown rice, cooked

Amount: 1 cup (19 µg)
%DV: 35%

Oatmeal, cooked

Amount: 1 cup (13 µg)
%DV: 24%

Choosing a product

What to look for on the label — and what to be skeptical of.

Look for…

L-selenomethionine fraction disclosed (60–85% is typical for high-quality Se-yeast; e.g. SelenoExcell, Sel-Plex)

Per-capsule elemental selenium dose stated in µg (typically 100 or 200 µg)

Third-party tested (USP, NSF, ConsumerLab) — the 2008 selenosis outbreak was from a mislabeled product with 200× the stated dose

Single-ingredient capsule if you're tracking total selenium intake precisely

100 µg/day formulations are a safer default for adults who get some selenium from food

Be skeptical of…

Claims of cancer prevention — SELECT was negative; the NPC secondary signals didn't replicate; long-term use carries a T2DM signal

'Antioxidant' or 'longevity' marketing on high-dose products for healthy adults — biomarker change without clinical-outcome support

Mega-dose products (400+ µg per serving) for daily use — at or above the UL with no benefit and real toxicity risk

Combination products that stack Se-yeast PLUS pure selenomethionine PLUS a multivitamin — total dose easily exceeds the UL

Liquid 'mineral concentrates' from unknown sources — the 2008 mass selenosis outbreak was from this category

'Naturally bound' or 'most bioavailable' superiority claims over pure L-selenomethionine — comparable in head-to-head trials

Frequently asked questions

Is selenium yeast better than other selenium forms?⌄

Selenium yeast is generally more bioavailable and retained in body tissues than inorganic forms like selenite. It is similar to isolated selenomethionine in effect.

Can I just eat Brazil nuts instead?⌄

Yes. Brazil nuts are the densest food source of selenium. One nut can provide more than a full daily requirement; eating more than 2-3 per day may exceed the upper limit.

Should I take selenium for my thyroid?⌄

Selenium supplementation can reduce thyroid antibodies in autoimmune thyroiditis. Consult your clinician, especially if you take thyroid medications.

Will selenium prevent cancer?⌄

Despite early enthusiasm, larger trials have not shown benefit and some have suggested risks (particularly increased prostate cancer risk in well-selenium-replete men). Don't supplement for cancer prevention without medical advice.

How do I know if I need a selenium supplement?⌄

Most adults in the US, Canada, and Western Europe get adequate selenium from food. People in regions with low soil selenium (parts of China, New Zealand, certain European areas) may benefit from supplementation.

References by claim

Cancer prevention

Clark et al. (NPC trial), 1996 — JAMA (1996) link

Stranges et al. (NPC follow-up), 2007 — Annals of Internal Medicine (2007) link

Rayman, 2012 — The Lancet (2012) link

Correcting selenium deficiency

NIH Office of Dietary Supplements — Selenium — Health Professional Fact Sheet (2024) link

Burk & Hill, 2015 — PMC — Annual Review of Nutrition (2015) link

Stranges et al. (PRECISE pilot), 2014 — PMC — PLoS ONE (2014) link

Safety

MacFarquhar et al., 2010 — Archives of Internal Medicine (2010) link

Chemotherapy / radiation mucositis (head & neck cancer)

Karp et al., 2013 — Journal of Clinical Oncology (2013) link

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Evidence-based·Last reviewed May 31, 2026·Evidence current as of May 31, 2026·How we grade evidence

Disclaimer: These statements have not been evaluated by the FDA. This page is educational, not a substitute for personalized medical advice. Evidence grades are AI-assisted assessments — talk to your doctor before starting any new supplement, especially if you’re pregnant, breastfeeding, on medications, or managing a chronic condition.