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Selenium
Most people in the US and Europe should not take a selenium supplement.
- 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.
- →Nature Made Selenium 200 mcg ($0.04/day) is the top pick as the only USP-verified option; NOW Foods ($0.03/day) is the value pick; Thorne ($0.20/day) for tested athletes.
- →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?
Most people in the US and Europe should not take a selenium supplement. Diet already covers it, Brazil nuts, seafood, organ meats, and grains from selenium-rich soil are reliable sources, and the dose-response curve is U-shaped, meaning supplementing above adequate status may cause harm. The cancer-prevention pitch collapsed when the SELECT trial (over 35,000 men) found no prostate cancer benefit and a follow-up signaled increased high-grade prostate cancer in already-replete men. The one real use case is Hashimoto's thyroiditis, where 200mcg/day reliably reduces TPO antibodies. Otherwise, "just in case" selenium is not harmless.
The most heavily marketed claim - cancer prevention - took a devastating hit. The largest and most rigorous trial (over 35,000 men) found selenium supplementation did NOT reduce prostate cancer risk. A follow-up analysis actually found a significant increase in high-grade prostate cancer in men who already had adequate selenium levels. An earlier, smaller trial had suggested benefit, but it was never replicated. The cancer prevention story for selenium is effectively dead in well-nourished populations.
Where selenium has real utility is thyroid health. Multiple trials in patients with Hashimoto's thyroiditis show that 200mcg/day significantly reduces thyroid antibody levels. Reviews confirm this effect, though whether it translates to fewer patients progressing to full hypothyroidism remains unclear. Selenium is a reasonable adjunct for Hashimoto's patients, particularly those with low selenium levels.
The critical context here is the U-shaped dose-response curve. Selenium supplementation benefits people who are deficient, but supplementing above adequate status appears to cause harm. SELECT's diabetes signal (a non-significant trend toward increased type 2 diabetes risk with selenium supplementation) was concerning and consistent with observational data showing a positive association between high selenium status and diabetes prevalence. The takeaway: if you eat a varied diet in North America, you probably do not need supplemental selenium, and taking it "just in case" is not harmless. If you have Hashimoto's or live in a selenium-poor region (parts of China, parts of Europe), it may be worth discussing with your doctor.
Selenomethionine is the preferred form - it is incorporated into body proteins in place of methionine, creating a selenium reserve. Sodium selenite is cheaper but less bioavailable and not stored the same way. Selenium yeast contains a mix of organic selenium compounds, predominantly selenomethionine, and is also well absorbed.
Does It Work? The Evidence
How A-F grades workThyroid 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
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.
General cancer prevention
NPC trial (Clark et al. 1996) - secondary endpoint positive; SELECT - negative; Cochrane 2018 review of selenium for cancer - insufficient evidence
Antioxidant defense and immune function
Selenoproteins (glutathione peroxidase, thioredoxin reductase) are well-characterized antioxidant enzymes; clinical benefits seen primarily in deficient populations
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 |
|---|---|---|---|
| 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 |
| 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 |
| 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 |
| 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 | 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 with food for best absorption. Selenomethionine can be taken with or without food, but taking it with a meal reduces the chance of GI upset. Do not exceed 200 mcg/day from supplements without medical supervision - the RDA is only 55 mcg, and most people get 100-150 mcg from diet alone in North America. If supplementing for thyroid support, 200 mcg/day of selenomethionine is the dose used in most Hashimoto's RCTs. Do not take selenium at the same time as high-dose vitamin C (above 500 mg), as in vitro studies suggest vitamin C may reduce selenite absorption - though this interaction is less relevant for selenomethionine. Pairing with adequate iodine intake is important for thyroid function, as selenium and iodine work together in thyroid hormone metabolism.
Who Should Take Selenium?
People with documented selenium deficiency or insufficiency (serum selenium below 70 mcg/L). Patients with Hashimoto's thyroiditis, where multiple RCTs support 200 mcg/day for reducing TPO antibodies - discuss with your endocrinologist. Those living in selenium-poor regions (parts of China, Finland, New Zealand, and some areas of Europe where soil selenium is low). People with malabsorptive conditions (Crohn's disease, celiac disease, short bowel syndrome) who may not absorb adequate selenium from food. Individuals on long-term parenteral nutrition without selenium supplementation.
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.
Prices checked 2026-04-01. Cost shown is per clinically effective daily dose, not per pill.
Pure Encapsulations Selenium (selenomethionine) 200 mcg
Pure Encapsulations$30.60 ÷ 180 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 2026-04-01. Cost shown is per clinically effective daily dose, not per pill.
NOW Foods Selenium 200 mcg
NOW Foods$6.49 ÷ 162 days at ~222mcg/day (1.1 servings × 200mcg)
Best cost-per-dose in the category from a reputable manufacturer. Selenium yeast form is well-studied and well-absorbed.
Prices checked 2026-04-01. 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.
Life Extension Super Selenium Complex 200 mcg
Life Extension$8.25 ÷ 103 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 2026-04-01. Cost shown is per clinically effective daily dose, not per pill.
Nutricost Selenium 200 mcg
Nutricost$7.95 ÷ 265 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 2026-04-01. 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 | NOW Foods Selenium 200 mcg NOW Foods | Doctor's Best Selenium 200 mcg Doctor's Best | 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 | 90/100 | 88/100 | 87/100 | 86/100 | 84/100 | 82/100 | 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 | 17/25 | 15/25 | 23/25 | 22/25 | 19/25 | 23/25 | 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 | $0.04 | $0.20 | $0.17 | $0.04 | $0.05 | $0.08 | $0.03Winner | $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 | selenium yeast veg capsule | selenomethionine (SeLECT branded) 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.
FDA Disclaimer: These statements have not been evaluated by the Food and Drug Administration. The products discussed on this page are not intended to diagnose, treat, cure, or prevent any disease. Always consult with a qualified healthcare professional before starting any supplement regimen.