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Selenium
Bottom line
In our scoring, Selenium rates mixed evidence: the evidence is mixed for thyroid function and Hashimoto's antibody reduction. Our top-scored product is Thorne Selenomethionine 200 mcg (88/100), about $0.20 a day at a clinical dose of 55-200 mcg daily. Bottom line: promising but not settled, so manage expectations. This is our opinion, not medical advice; talk to your clinician before starting.
Selenium runs against the "a little more can't hurt" instinct most people bring to minerals: in the US or Europe you probably should not take it at all.
- Evidence
- Mixed Evidence
- Category
- Vitamins & Minerals
- Best form
- selenomethionine (organic, best absorbed)
- Effective dose
- 55-200 mcg daily
- Lab tested
- 7 of 10 products
- Category
- Vitamins & Minerals
- Best form
- selenomethionine (organic, best absorbed)
- Effective dose
- 55-200 mcg daily
- Lab tested
- 7 of 10 products
Key takeaways
- →The cancer prevention story is dead - the real utility is thyroid: 200 mcg/day reduces TPO antibodies in Hashimoto's patients.
- →Use selenomethionine (~90% absorbed) or selenium yeast - not sodium selenite. Most US adults already get 100-150 mcg from diet; do not exceed 400 mcg/day total.
- →Thorne ($0.20/day, NSF Certified for Sport) is our top pick among buyable options; Nutricost ($0.06/day) is the value pick after a category-wide 2026 repricing; Nature Made remains the only USP-verified option when in stock.
- →U-shaped dose-response curve: replete people may be harmed by extra selenium - one Brazil nut delivers 68-91 mcg, so 3-4 daily can push you over the ceiling.
What Is Selenium?
Selenium runs against the "a little more can't hurt" instinct most people bring to minerals: in the US or Europe you probably should not take it at all. Your diet almost certainly already covers it. Brazil nuts, seafood, organ meats, and grains grown in selenium-rich soil are reliable sources, and the gap between "enough" and "too much" is narrow - more is not better here, and going above an adequate level may actually cause harm. So the question is not "is selenium good?" but "do you personally have a reason to add it?" For most people the honest answer is no. The popular cancer-prevention pitch fell apart when the SELECT trial (over 35,000 men) found no prostate cancer benefit, and the one place selenium clearly earns its keep is Hashimoto's thyroiditis, where 200mcg/day reliably lowers TPO antibodies.
The pitch you have probably heard - that selenium helps prevent cancer - took a hard hit. The largest, most carefully run trial (the SELECT trial, over 35,000 men) found that selenium did NOT reduce prostate cancer risk. A follow-up analysis went further: in men who already had enough selenium, it found a significant increase in high-grade prostate cancer. An earlier, smaller study had hinted at a benefit, but no one was able to repeat it. In well-fed populations, the cancer story is effectively over.
There is one place selenium earns its keep: Hashimoto's thyroiditis (an autoimmune thyroid condition). Several trials show that 200mcg/day lowers TPO antibodies, a marker of that immune attack on the thyroid. Reviews back this up. What is still unclear is whether fewer antibodies actually means fewer people go on to develop full hypothyroidism - that link has not been proven. So selenium is a reasonable add-on for Hashimoto's patients, especially those who are low to begin with, and a conversation to have with your doctor rather than a solo decision.
The thread running through all of this is that selenium helps when you are short on it and can hurt when you are not (researchers call this a U-shaped dose-response curve - benefit in the dip, trouble at both ends). SELECT also turned up a diabetes signal: a trend toward more type 2 diabetes in people taking selenium. It did not reach statistical significance, but it lined up with other data tying high selenium to more diabetes, so it is worth knowing. The practical read: if you eat a varied diet in North America, "just in case" selenium is not a free move - it carries a real downside. If you have Hashimoto's or live somewhere the soil runs low on selenium (parts of China, parts of Europe), that is a different conversation, and one to have with your doctor.
On forms, selenomethionine is the one to look for. Your body slots it into proteins in place of methionine (an amino acid), which builds up a small selenium reserve. Sodium selenite is cheaper but your body absorbs less of it and does not store it the same way. Selenium yeast is a mix of organic selenium compounds, mostly selenomethionine, and is also well absorbed.
Does It Work? The Evidence
How A-F grades workSelenium earns a Mixed Evidence rating: the research is suggestive but not settled. Its best-supported uses so far are thyroid function and Hashimoto's antibody reduction and antioxidant defense and immune function (grade B), but the evidence across claims is mixed - each is graded on its own below.
Prostate cancer prevention
SELECT trial (JAMA 2009, n=35,533) - no benefit; follow-up JNCI 2014 - possible harm in selenium-replete men. Clark et al. JAMA 1996 - positive but not replicated.
Thyroid function and Hashimoto's antibody reduction
Wichman et al. Thyroid 2016 meta-analysis; Cochrane review 2010; multiple RCTs showing TPO antibody reduction at 200 mcg/day
Antioxidant defense and immune function
Selenoproteins (glutathione peroxidase, thioredoxin reductase) are well-characterized antioxidant enzymes; clinical benefits seen primarily in deficient populations
General cancer prevention
NPC trial (Clark et al. 1996) - secondary endpoint positive; SELECT - negative; Cochrane 2018 review of selenium for cancer - insufficient evidence
Cardiovascular disease prevention
Observational studies show mixed results; Cochrane 2013 review found no clear evidence for CVD prevention from selenium supplementation
Cognitive function preservation
Small observational studies link low selenium to cognitive decline; no large RCTs support supplementation for cognition
| Grade | Claimed Benefit | Key Studies | Our Verdict |
|---|---|---|---|
| A | Prostate cancer prevention | SELECT trial (JAMA 2009, n=35,533) - no benefit; follow-up JNCI 2014 - possible harm in selenium-replete men. Clark et al. JAMA 1996 - positive but not replicated. | Ineffective |
| B | Thyroid function and Hashimoto's antibody reduction | Wichman et al. Thyroid 2016 meta-analysis; Cochrane review 2010; multiple RCTs showing TPO antibody reduction at 200 mcg/day | Supported |
| B | Antioxidant defense and immune function | Selenoproteins (glutathione peroxidase, thioredoxin reductase) are well-characterized antioxidant enzymes; clinical benefits seen primarily in deficient populations | Supported |
| C | General cancer prevention | NPC trial (Clark et al. 1996) - secondary endpoint positive; SELECT - negative; Cochrane 2018 review of selenium for cancer - insufficient evidence | Not There Yet |
| C | Cardiovascular disease prevention | Observational studies show mixed results; Cochrane 2013 review found no clear evidence for CVD prevention from selenium supplementation | Not There Yet |
| D | Cognitive function preservation | Small observational studies link low selenium to cognitive decline; no large RCTs support supplementation for cognition | Not There Yet |
How to Choose: Forms, Doses & What Matters
Clinical dose: 55-200 mcg daily; RDA is 55 mcg for adults, upper tolerable limit is 400 mcg/day
Best forms: selenomethionine (organic, best absorbed), selenium yeast (mixed organic forms), sodium selenite (inorganic, lower bioavailability)
Take it with a meal. Selenomethionine works with or without food, but a meal cuts the chance of stomach upset. The number to respect is the ceiling: do not go past 200 mcg/day from supplements without a doctor's guidance. For context, the official daily target (RDA) is just 55 mcg, and most people in North America already get 100-150 mcg from food, so a supplement stacks on top of a base you may not have measured. If you are taking it for thyroid support, 200 mcg/day of selenomethionine is the dose used in most Hashimoto's trials. One timing note: keep it separate from a big dose of vitamin C (above 500 mg), since lab studies suggest vitamin C can cut down on selenite absorption - that matters less for selenomethionine, but spacing them is easy enough. And make sure you are getting enough iodine, because selenium and iodine work as a pair in how your body makes thyroid hormone.
Who Should Take Selenium?
This is a short list on purpose. You have a real reason to consider selenium if a blood test has shown you are low (serum selenium below 70 mcg/L) - not a guess, an actual number. You may also have a reason if you have Hashimoto's thyroiditis, where multiple trials support 200 mcg/day for lowering TPO antibodies, though that is a call to make with your endocrinologist, not on your own. The same goes if you live somewhere the soil is low in selenium (parts of China, Finland, New Zealand, and some areas of Europe), so your local food carries less of it. Two other groups: people whose gut does not absorb nutrients well (Crohn's disease, celiac disease, short bowel syndrome), who may not pull enough selenium from food, and people fed long-term through an IV (parenteral nutrition) that does not include selenium.
Who Should Avoid It?
Not for everyone
Side Effects & Safety
Product Scores
10 products scored on dosing accuracy, third-party testing, cost per effective dose, and label transparency.
The Scorecard: 10 Products Compared
Nature Made Selenium 200 mcg
Nature Made$10.49 ÷ 262 days at 200mcg/day (1 serving × 200mcg)
USP Verified at bottom-tier pricing. The obvious default choice for anyone who actually needs selenium supplementation.
Prices checked 2026-04-01. Cost shown is per clinically effective daily dose, not per pill.
Thorne Selenomethionine 200 mcg
Thorne$12.00 ÷ 60 days at 200mcg/day (1 serving × 200mcg)
NSF Certified for Sport makes this the clear choice for competitive athletes who undergo drug testing, even after a 2026 price rise widened the gap to the budget options.
Prices checked 2026-07-07. Cost shown is per clinically effective daily dose, not per pill.
Pure Encapsulations Selenium (selenomethionine) 200 mcg
Pure Encapsulations$37.50 ÷ 179 days at 200mcg/day (1 serving × 200mcg)
The cleanest formulation on this list. Best option for people with multiple food sensitivities or autoimmune conditions requiring minimal excipients.
Prices checked 2026-06-11. Cost shown is per clinically effective daily dose, not per pill.
Doctor's Best Selenium 200 mcg
Doctor's Best$8.97 ÷ 179 days at 200mcg/day (1 serving × 200mcg)
Uses a branded selenomethionine ingredient. Good value for the preferred form, but lacks the independent certification that separates B-tier from A-tier.
Prices checked 2026-04-01. Cost shown is per clinically effective daily dose, not per pill.
NOW Foods Selenium 200 mcg
NOW Foods$12.24 ÷ 175 days at 200mcg/day (1 serving × 200mcg)
A solid budget option from a reputable manufacturer, though its 2026 repricing handed the cost-per-dose crown to Nutricost. Selenium yeast form is well-studied and well-absorbed.
Prices checked 2026-06-11. Cost shown is per clinically effective daily dose, not per pill.
Life Extension Super Selenium Complex 200 mcg
Life Extension$10.50 ÷ 95 days at 200mcg/day (1 serving × 200mcg)
Multi-form selenium approach is theoretically interesting but lacks comparative RCT data vs. selenomethionine alone. Added vitamin E is a small dose.
Prices checked 2026-06-11. Cost shown is per clinically effective daily dose, not per pill.
Nutricost Selenium 200 mcg
Nutricost$13.95 ÷ 233 days at 200mcg/day (1 serving × 200mcg)
Budget-tier pricing with the right form and dose, but the absence of independent testing certification is a real issue for a trace mineral where the therapeutic dose and the toxic dose are not far apart.
Prices checked 2026-06-11. Cost shown is per clinically effective daily dose, not per pill.
Solgar Selenium 200 mcg
Solgar$10.99 ÷ 100 days at 200mcg/day (1 serving × 200mcg)
Uses sodium selenate rather than selenomethionine. Not the preferred form based on clinical literature. Priced above competitors offering the better form.
Prices checked 2026-04-01. Cost shown is per clinically effective daily dose, not per pill.
Bronson Selenium 200 mcg
Bronson
$9.99 ÷ 250 days at 200mcg/day (1 serving × 200mcg)
Inferior form (sodium selenite) with no independent testing. The low price reflects the low-cost raw material, not smart formulation. You can get selenomethionine from NOW Foods for the same price.
Prices checked 2026-04-01. Cost shown is per clinically effective daily dose, not per pill.
Carlyle Selenium 200 mcg
Carlyle
$9.78 ÷ 196 days at 200mcg/day (1 serving × 200mcg)
Inferior selenium form, no recognized third-party certification, and Amazon's private-label supplements have a spotty track record. The QR code transparency feature is marketing, not quality assurance.
Prices checked 2026-04-01. Cost shown is per clinically effective daily dose, not per pill.
Full Comparison
| Category | Nature Made Selenium 200 mcg Nature Made | Thorne Selenomethionine 200 mcg Thorne | Pure Encapsulations Selenium (selenomethionine) 200 mcg Pure Encapsulations | Doctor's Best Selenium 200 mcg Doctor's Best | NOW Foods Selenium 200 mcg NOW Foods | Life Extension Super Selenium Complex 200 mcg Life Extension | Nutricost Selenium 200 mcg Nutricost | Solgar Selenium 200 mcg Solgar | Bronson Selenium 200 mcg Bronson | Carlyle Selenium 200 mcg Carlyle |
|---|---|---|---|---|---|---|---|---|---|---|
| Brand Score | 96/100Winner | 88/100 | 87/100 | 86/100 | 85/100 | 83/100 | 81/100 | 80/100 | 75/100 | 69/100 |
| Dosing & Form | 25/25Winner | 25/25 | 25/25 | 25/25 | 25/25 | 25/25 | 25/25 | 25/25 | 25/25 | 25/25 |
| Purity | 25/25Winner | 25/25 | 23/25 | 19/25 | 19/25 | 20/25 | 15/25 | 19/25 | 13/25 | 11/25 |
| Value | 23/25Winner | 15/25 | 14/25 | 22/25 | 21/25 | 18/25 | 22/25 | 17/25 | 22/25 | 20/25 |
| Transparency | 23/25 | 23/25 | 25/25Winner | 20/25 | 20/25 | 20/25 | 19/25 | 19/25 | 15/25 | 13/25 |
| Cost/Day | $0.04Winner | $0.20 | $0.21 | $0.05 | $0.07 | $0.11 | $0.06 | $0.11 | $0.04 | $0.05 |
| Dose/Serving | 200mcg | 200mcg | 200mcg | 200mcg | 200mcg | 200mcg | 200mcg | 200mcg | 200mcg | 200mcg |
| Form | selenomethionine tablet | selenomethionine capsule | selenomethionine hypoallergenic capsule | selenomethionine (SeLECT branded) veg capsule | selenium yeast veg capsule | selenomethionine + sodium selenite + Se-methylselenocysteine blend, capsule | selenomethionine capsule | sodium selenate tablet | sodium selenite tablet | sodium selenite capsule |
| Third-Party Tested | ✓ Yes | ✓ Yes | ✓ Yes | ✓ Yes | ✓ Yes | ✓ Yes | No | ✓ Yes | No | No |
| Proprietary Blend | No | No | No | No | No | No | No | No | No | No |
Frequently Asked Questions
Do I need a selenium supplement if I eat a normal diet?
Probably not. The average American diet provides about 100-150 mcg of selenium per day, which is well above the 55 mcg RDA. Selenium is found in Brazil nuts (one nut provides 68-91 mcg), seafood, organ meats, poultry, eggs, and grains. Deficiency is rare in North America but more common in parts of China, Russia, and Europe where soil selenium is low. A blood test measuring serum selenium can confirm your status if you are concerned.
What happened with selenium and cancer prevention?
The cancer story collapsed with the SELECT trial. An earlier study (Clark et al. 1996, n=1,312) found that selenium supplementation appeared to reduce prostate cancer incidence by about 50% - but that was a secondary endpoint, not what the study was designed to test. SELECT (JAMA 2009, n=35,533) was a massive, well-designed trial specifically built to test this claim. It found no reduction in prostate cancer with 200 mcg/day selenomethionine. A follow-up analysis found selenium may actually increase high-grade prostate cancer risk in men who already had adequate selenium levels. This is a case study in why secondary endpoints need replication.
Is selenomethionine better than sodium selenite?
Yes, for most supplementation purposes. Selenomethionine is an organic form that is approximately 90% absorbed and is incorporated into body proteins as a selenium reserve. Sodium selenite is an inorganic form with lower bioavailability (about 50% absorbed) and is not stored in proteins the same way. Most clinical trials showing benefits in Hashimoto's patients used selenomethionine. Selenium yeast (which contains mostly selenomethionine) is also a good option. The one exception: some researchers argue selenite may be preferable for acute antioxidant effects because it is not sequestered in proteins, but the clinical evidence for this distinction is thin.
Can selenium help with thyroid problems?
For Hashimoto's thyroiditis specifically, yes - with caveats. Multiple RCTs have shown that 200 mcg/day of selenomethionine reduces TPO (thyroid peroxidase) antibody levels in Hashimoto's patients, typically by 20-40% over 3-12 months. However, it remains unclear whether this antibody reduction translates to meaningful clinical outcomes like preventing progression to overt hypothyroidism. Selenium is also required for the deiodinase enzymes that convert T4 to active T3. For general thyroid support, ensuring adequate selenium intake through diet is sensible - supplementation is most justified when deficiency is documented or in autoimmune thyroid disease.
What are the signs of selenium deficiency?
Mild deficiency may not cause obvious symptoms. More significant deficiency can cause fatigue, brain fog, weakened immune function, hair loss, and thyroid dysfunction. Severe deficiency is rare in developed countries but can cause Keshan disease (a cardiomyopathy first identified in selenium-poor regions of China) and Kashin-Beck disease (an osteoarthropathy). Risk factors include living in selenium-poor regions, malabsorptive conditions (Crohn's, celiac), chronic kidney disease requiring dialysis, and HIV infection.
Can I just eat Brazil nuts instead of taking a supplement?
Yes, and for most people this is the better approach. A single Brazil nut contains roughly 68-91 mcg of selenium, so 1-2 nuts per day can easily meet the 55 mcg RDA and push into the 100-200 mcg range used in clinical trials. This is cheaper than any supplement and comes with healthy fats and other minerals. The caveat: selenium content in Brazil nuts varies significantly depending on the soil where the trees grew, so dosing is less precise than a supplement. Do not eat more than 3-4 Brazil nuts daily on a regular basis - it is surprisingly easy to exceed the 400 mcg upper limit with this food.
Related Articles
Sources
- Lippman SM, et al. Effect of selenium and vitamin E on risk of prostate cancer and other cancers: the Selenium and Vitamin E Cancer Prevention Trial (SELECT). JAMA. 2009;301(1):39-51.
- Clark LC, et al. Effects of selenium supplementation for cancer prevention in patients with carcinoma of the skin. A randomized controlled trial (NPC trial). JAMA. 1996;276(24):1957-1963.
- Kristal AR, et al. Baseline selenium status and effects of selenium and vitamin E supplementation on prostate cancer risk. J Natl Cancer Inst. 2014;106(3):djt456.
- Wichman J, et al. Selenium supplementation significantly reduces thyroid autoantibody levels in patients with chronic autoimmune thyroiditis: a systematic review and meta-analysis. Thyroid. 2016;26(12):1681-1692.
- NIH Office of Dietary Supplements. Selenium Fact Sheet for Health Professionals. Updated 2024.
- Vinceti M, et al. Selenium for preventing cancer. Cochrane Database Syst Rev. 2018;1(1):CD005195.
- Rayman MP. Selenium and human health. Lancet. 2012;379(9822):1256-1268.
- Stranges S, et al. Effects of long-term selenium supplementation on the incidence of type 2 diabetes: a randomized trial. Ann Intern Med. 2007;147(4):217-223.
Scores and tiers are our independent opinion, formed by applying a published rubric to label data, third-party certifications, and the research record. They are not statements of objective fact about a product and not a lab test. Where we report a brand-specific fact, it comes from a cited source or a public certification; where verification is missing, we say so rather than assume a result.
FDA Disclaimer: These statements have not been evaluated by the Food and Drug Administration. Dietary supplements are not intended to diagnose, treat, cure, or prevent any disease. Always consult with a qualified healthcare professional before starting any supplement regimen.