Does selenium help Hashimoto's and thyroid health?

In Hashimoto's thyroiditis, selenium lowers thyroid peroxidase antibodies. A 2024 meta-analysis pooled 29 trial cohorts with 2,358 people and found a standardized fall of 0.96, with heterogeneity of 90 percent between trials. The largest single trial then asked whether that makes patients better off. In 412 people on levothyroxine, 200 micrograms a day for 12 months improved quality of life no more than placebo and did not change the levothyroxine dose. The one place selenium has a clinical effect is mild Graves' eye disease, in regions where people are short of it.

Unsettled. Selenium changes a blood test in Hashimoto's. No trial we found shows that the lower antibody count slows the disease, prevents hypothyroidism or lets anyone take less levothyroxine. An overview of six systematic reviews covering 75 trials rated the antibody evidence as low or very low certainty.

What the trials found

Hashimoto's: antibodies down, TSH barely moves

The same 2024 meta-analysis of 35 studies found selenium lowered TSH slightly in people not on thyroid hormone, a standardized difference of minus 0.21 with a confidence interval from minus 0.43 to minus 0.02, across 7 cohorts and 869 participants. The authors rated the evidence moderate certainty overall. Free T4, T3 and thyroid volume did not change. A newer 2025 meta-analysis of 21 randomized trials in 1,610 people agrees on the direction. Antibodies fell at 3 months (minus 0.46, interval minus 0.74 to minus 0.18) and at 6 months (minus 0.80, interval minus 1.38 to minus 0.21), and TSH fell a little at 6 months (minus 0.18).

Against that, a 2017 meta-analysis of 9 controlled trials in people not on levothyroxine found no effect on TSH, on health-related quality of life or on the thyroid ultrasound. The 2013 Cochrane review found only four randomized trials with 463 people, at unclear to high risk of bias, and said they do not allow confident decisions. We found no Cochrane update since.

Myth. Selenium will not make Hashimoto's feel better. In the CATALYST trial, 412 adults with autoimmune hypothyroidism on levothyroxine took 200 micrograms a day or placebo for 12 months. Quality of life improved to the same extent in both groups, 28.8 against 28.0 on the trial's composite score, with P = 0.602. Antibodies ended somewhat lower on selenium, 1,995 against 2,344 kIU/L, and the levothyroxine dose did not change.

Graves' hyperthyroidism: no effect

In the GRASS trial, 430 people with newly diagnosed Graves' hyperthyroidism took antithyroid drugs plus 200 micrograms of selenium or placebo for 24 to 30 months. 54.6 percent on selenium and 53.3 percent on placebo were still not in remission, an odds ratio of 1.0 (0.7 to 1.5). Quality of life and TSH receptor antibodies did not differ either.

Graves' eye disease: the one clinical benefit

Established. In mild Graves' orbitopathy, six months of selenium helps the eyes. A 2024 meta-analysis of 4 randomized trials found the clinical activity score fell by 1.27 points (interval 0.85 to 1.68) and the chance of better eye-related quality of life was 2.54 times higher (1.69 to 3.81). Bulging of the eye and eye movement did not differ. Four trials is a small base.

The best-known of those trials, published in 2011, gave 159 people with mild Graves' orbitopathy 100 micrograms of selenium twice a day for 6 months. Against placebo they had better quality of life, less eye involvement and slower progression. Those patients lived in European regions with borderline selenium status, so the result does not transfer to people who already get enough.

Status changes the answer

In a 4-year trial in 414 older Swedes with low selenium intake and no thyroid disease, selenium yeast at 200 micrograms combined with coenzyme Q10 raised free T3 and lowered free T4, and blunted the rise in TSH against placebo. The combination means selenium's own share cannot be separated, and most Hashimoto's trials never measured selenium status at the start.

Who should be careful

Not for everyone. Pregnant women with thyroid antibodies. One randomized trial in 151 such women in Italy found 200 micrograms of selenomethionine a day cut postpartum thyroid dysfunction from 48.6 to 28.6 percent, and permanent hypothyroidism from 20.3 to 11.7 percent. In 2017 the American Thyroid Association still issued a weak recommendation against selenium for these women, on moderate quality evidence. That decision belongs with the doctor following the pregnancy.

The ceiling is low relative to the dose sold for the thyroid. The US upper limit for adults is 400 micrograms a day. In 2023 the European Food Safety Authority set 255 micrograms a day for all adults, including during pregnancy and breastfeeding, based on hair loss. A 200 microgram tablet plus an ordinary diet can pass the European limit. Brazil nuts make this worse: a single nut can hold 68 to 91 micrograms, and in one laboratory test of eight nuts from five batches the selenium content differed twentyfold, from 0.25 to 5.06 micrograms per gram.

Long-term harms come from cancer-prevention trials that lasted years. A Cochrane review of those selenium trials found that the randomized trials showed a slightly higher risk of type 2 diabetes with supplementation, and the European upper limit itself rests on hair loss. Whether that applies to a 6 or 12 month course for Hashimoto's is unknown. The trial syntheses also disagree on side effects. A 2016 meta-analysis of 16 controlled trials found people on selenium reported adverse effects significantly more often (p = 0.036). The 2024 meta-analysis found an odds ratio of 0.89, with an interval from 0.46 to 1.75.

What expert bodies say

The NIH Office of Dietary Supplements summarizes the trials the way this page does. Selenium can lower some thyroid antibodies in chronic autoimmune thyroiditis, and other trials found no effect on thyroid function or quality of life. The 2021 European guideline on Graves' orbitopathy, from EUGOGO, says that in mild and active disease, control of risk factors, local treatment and selenium are usually sufficient, and it limits selenium to selenium-deficient areas. The American Thyroid Association advises against it in pregnant women with antibodies. In the European Union, food labels may say that selenium contributes to normal thyroid function. That authorized wording describes a body function. It says nothing about treating Hashimoto's or any other disease.

How we searched

What would change this answer

• A trial showing that lowering antibodies with selenium delays hypothyroidism or reduces the levothyroxine dose. Nothing we found tested this directly, and CATALYST saw no change in dose.
• Hashimoto's trials that measure selenium status first and report results separately for people who are short of it. The Swedish and orbitopathy data both point to the effect living there.
• A second randomized trial in pregnant women with thyroid antibodies. One positive trial against a professional recommendation is an open question.
• A trial of selenium from food, such as Brazil nuts or fish, on any thyroid outcome. We found none. One trial now recruiting combines myo-inositol with selenium for thyroid nodules, which will not answer the question for selenium alone.

More on selenium itself, including how much you need and where it comes from: the selenium guide and the Brazil nuts page.

Sources

1. ev-selth-01 · Meta-analysis or systematic review · systematic review and meta-analysis of RCTs, GRADE · n = 869
   Our meta-analysis found that selenium supplementation decreased TSH in patients without THRT (SMD -0.21 [confidence interval, CI -0.43 to -0.02]; 7 cohorts, 869 participants; I2 = 0%).
   
   Who: patients with Hashimoto thyroiditis in randomized trials; TSH outcome in those without thyroid hormone replacement
   Effect: TSH SMD -0.21 (95% CI -0.43 to -0.02), 7 cohorts, I2 = 0%; TPOAb SMD -0.96 (-1.36 to -0.56), 29 cohorts, 2358 participants, I2 = 90%; adverse events OR 0.89 (0.46 to 1.75); overall certainty of evidence moderate (GRADE)
   Certainty: The most complete synthesis (Thyroid 2024, search to 01.2023). Effect on antibodies with very high heterogeneity; almost no clinical endpoints.
   Thyroid, 2024 · checked 2026-10-07 · we read the abstract
2. ev-selth-02 · Meta-analysis or systematic review · systematic review and meta-analysis of RCTs, GRADE · n = 2358
   In addition, TPOAb (SMD -0.96 [CI -1.36 to -0.56]; 29 cohorts; 2358 participants; I2 = 90%) and malondialdehyde (MDA; SMD -1.16 [CI -2.29 to -0.02]; 3 cohorts; 248 participants; I2 = 85%) decreased in patients with and without THRT.
   
   Who: patients with Hashimoto thyroiditis with and without thyroid hormone replacement
   Effect: TPOAb SMD -0.96 (95% CI -1.36 to -0.56); I2 = 90%; no significant change in fT4, T4, fT3, T3, TGAb or thyroid volume
   Certainty: Antibodies are a surrogate; it has not been shown that lowering TPOAb changes the course of the disease.
   Thyroid, 2024 · checked 2026-10-07 · we read the abstract
3. ev-selth-03 · Meta-analysis or systematic review · systematic review and meta-analysis of RCTs · n = 1610
   Serum TPOAb was significantly reduced after Se supplementation after 3 months (standardized mean difference [SMD] = -0.46, 95% confidence interval [CI]: -0.74 to -0.18, P = .001) and 6 months (SMD = -0.80, 95%CI: -1.38 to -0.21, P = .008).
   
   Who: patients with Hashimoto thyroiditis in randomized controlled trials
   Effect: TPOAb SMD -0.46 (95% CI -0.74 to -0.18) at 3 months, -0.80 (-1.38 to -0.21) at 6 months; TSH SMD -0.18 (-0.35 to -0.01) at 6 months
   Certainty: The newest MA; no certainty rating in the abstract. The conclusion about "well-being" is not supported by numbers in the abstract, so we do not take it.
   Medicine (Baltimore), 2025 · checked 2026-10-07 · we read the abstract
4. ev-selth-04 · Randomized controlled trial(s) · systematic review and meta-analysis of controlled trials, GRADE · n = 9 trials
   We found no effect of selenium supplementation on thyroid stimulating hormone, health-related quality of life or thyroid ultrasound, in levothyroxine substitution-untreated individuals, and sporadic evaluation of clinically relevant outcomes in levothyroxine substitution-treated patients.
   
   Who: adults with chronic autoimmune thyroiditis, levothyroxine-untreated, in controlled trials
   Effect: no change in TSH, health-related quality of life or thyroid echogenicity vs placebo; quality of evidence very low to moderate
   Certainty: Key "clinical" answer: antibodies fall, but well-being and function do not.
   Endocrine, 2017 · checked 2026-10-07 · we read the abstract
5. ev-selth-05 · Meta-analysis or systematic review · overview of systematic reviews with meta-analysis, AMSTAR-2 and GRADE · n = 75 RCTs
   Although selenium supplementation might reduce TPO-Ab levels at 3 and 6 months and Tg-Ab levels at 3 and 6 months in the non-LT4-treated population, this was based on a low certainty of evidence.
   
   Who: patients with autoimmune thyroiditis, with and without levothyroxine, in RCTs from 6 systematic reviews
   Effect: TPO-Ab SMD -0.53 (95% CI -0.89 to -0.17) at 3 months and -1.95 (-3.17 to -0.74) at 6 months in LT4-treated, very low certainty; no fall at 12 months in untreated
   Certainty: Only one review of six was rated high quality.
   Nutrients, 2023 · checked 2026-10-07 · we read the abstract
6. ev-selth-06 · Meta-analysis or systematic review · Cochrane systematic review of RCTs · n = 463
   The current level of evidence for the efficacy of selenium supplementation in the management of people with Hashimoto's thyroiditis is based on four randomised controlled trials assessed at unclear to high risk of bias; this does not at present allow confident decision making about the use of selenium supplementation for Hashimoto's thyroiditis.
   
   Who: adults with Hashimoto's thyroiditis in randomized controlled trials
   Effect: no pooled estimate (I2 = 99%); TPOAb fell with selenomethionine 200 micrograms in single trials; quality of life and LT4 dose not assessed
   Certainty: Old (search up to 2012), but the only Cochrane review; no update found (Europe PMC, 2024-2026).
   Cochrane Database Syst Rev, 2013 · checked 2026-10-07 · we read the abstract
7. ev-selth-07 · Randomized controlled trial(s) · multicentre double-blind randomized placebo-controlled trial · n = 412
   In hypothyroid patients on LT4 therapy due to autoimmune thyroiditis, daily supplementation with 200 μg selenium or placebo for 12 months improved QoL to the same extent.
   
   Who: 412 patients aged 18 or older with TPOAb at least 100 IU/mL on levothyroxine; 332 completed, 82% women
   Effect: ThyPRO-39 composite 28.8 (95% CI 24.5 to 33.6) vs 28.0 (24.5 to 33.1), P = 0.602; TPOAb lower with selenium (1995 vs 2344 kIU/L, P = 0.016) but no change in LT4 dose
   Certainty: The largest and cleanest RCT in Hashimoto's: antibodies slightly lower, no benefit for the patient. Outside the corpus; abstract from Europe PMC and E-utilities.
   Eur Thyroid J, 2024, Selenium supplementation and placebo are equally effective in improving quality of life in patients with hypothyroidism (CATALYST trial) · checked 2026-10-07 · we read the abstract
8. ev-selth-08 · Randomized controlled trial(s) · double-blind multicentre randomized placebo-controlled trial · n = 430
   Non-remission was observed in 114 (53.3%) participants in the placebo group and 118 (54.6%) in the selenium group (OR = 1.0 (95% CI: 0.7-1.5); P = 0.98).
   
   Who: individuals with newly diagnosed Graves' hyperthyroidism on antithyroid drugs, multicentre
   Effect: non-remission 54.6% with selenium vs 53.3% with placebo, OR 1.0 (95% CI 0.7 to 1.5); no difference on any ThyPRO scale or in TRAb
   Certainty: A clean null for Graves' hyperthyroidism (not for orbitopathy).
   Eur Thyroid J, 2026 · checked 2026-10-07 · we read the abstract
9. ev-selth-09 · Meta-analysis or systematic review · systematic review and meta-analysis of RCTs · n = 4 RCTs
   Selenium was superior at 6 months in lowering the CAS (MD = -1.27, 95% confidence interval [CI] [-1.68, -0.85], p < .0001]), improving total GO-QOL (RR = 2.54, 95% CI [1.69-3.81], p < .00001), and improving the visual and the psychological functioning scores (MD = 10.84, 95% CI [4.94-16.73], p = .003), (MD = 12.76, 95% CI [8.51-17.00], p < .00001) respectively.
   
   Who: patients with Graves' orbitopathy treated with selenium vs placebo
   Effect: CAS MD -1.27 (95% CI -1.68 to -0.85) at 6 months; GO-QOL improvement RR 2.54 (1.69 to 3.81); no difference in proptosis, motility or adverse effects
   Certainty: Only 4 RCTs; the strongest signal of selenium benefit in thyroidology, and it is about the eyes, not the thyroid.
   Clin Endocrinol (Oxf), 2024 · checked 2026-10-07 · we read the abstract
10. ev-selth-10 · Randomized controlled trial(s) · multicentre double-blind randomized placebo-controlled trial · n = 159
    At the 6-month evaluation, treatment with selenium, but not with pentoxifylline, was associated with an improved quality of life (P<0.001) and less eye involvement (P=0.01) and slowed the progression of Graves' orbitopathy (P=0.01), as compared with placebo.
    
    Who: 159 patients with mild Graves' orbitopathy; selenium 100 micrograms twice daily, pentoxifylline or placebo for 6 months, followed 6 more months
    Effect: improved GO quality of life (P < 0.001), less eye involvement (P = 0.01), slower progression (P = 0.01) vs placebo at 6 months; no adverse events with selenium
    Certainty: NEJM 2011; participants from regions with borderline selenium status (Europe), so this cannot be transferred to the well-supplied.
    N Engl J Med, 2011 · checked 2026-10-07 · we read the abstract
11. ev-selth-11 · Position of an expert body · clinical practice guideline · n = not applicable
    In mild and active GO, control of risk factors, local treatments, and selenium (selenium-deficient areas) are usually sufficient; if RAI treatment is selected to manage GD, low-dose oral prednisone prophylaxis is needed, especially if risk factors coexist.
    
    Who: patients with mild and active Graves' orbitopathy
    Effect: selenium recommended for mild active GO in selenium-deficient areas
    Certainty: Position of the relevant European society; the restriction "in deficiency areas" is substantial.
    Eur J Endocrinol, 2021 · checked 2026-10-07 · we read the abstract
12. ev-selth-12 · Randomized controlled trial(s) · prospective randomized placebo-controlled trial · n = 151
    PPTD and permanent hypothyroidism were significantly lower in group S1 compared with S0 (28.6 vs. 48.6%, P<0.01; and 11.7 vs. 20.3%, P<0.01).
    
    Who: euthyroid TPOAb-positive pregnant women; 77 selenomethionine 200 micrograms/day, 74 placebo, during pregnancy and postpartum
    Effect: postpartum thyroid dysfunction 28.6% vs 48.6% (P < 0.01); permanent hypothyroidism 11.7% vs 20.3% (P < 0.01)
    Certainty: A single RCT (Italy, borderline selenium status); other RCTs in pregnant women: zero; ATA against (see ev-selth-13).
    J Clin Endocrinol Metab, 2007 · checked 2026-10-07 · we read the abstract
13. ev-selth-13 · Position of an expert body · government fact sheet citing a society guideline · n = not applicable
    In 2017, the American Thyroid Association issued a weak recommendation against the use of selenium supplementation for pregnant women who are TPOAb positive based on moderate quality evidence [115].
    
    Who: pregnant women who are TPOAb positive
    Effect: weak recommendation against selenium supplementation (ATA 2017)
    Certainty: Discrepancy: one RCT for, ATA against because of mixed results and type 2 diabetes risk.
    NIH Office of Dietary Supplements, Selenium Fact Sheet for Health Professionals · checked 2026-10-07 · we read the section
14. ev-selth-14 · Position of an expert body · government fact sheet · n = not applicable
    Clinical trials have found that selenium supplementation can lower the levels of certain thyroid antibodies in people with chronic autoimmune thyroiditis, but other trials have reported no effect on thyroid function or the quality of life in these patients.
    
    Who: people with chronic autoimmune thyroiditis
    Effect: antibodies lowered in some trials; no effect on thyroid function or quality of life in others
    Certainty: Authority position matches the A/B cards above.
    NIH Office of Dietary Supplements, Selenium Fact Sheet for Health Professionals · checked 2026-10-07 · we read the section
15. ev-selth-15 · Position of an expert body · government fact sheet · n = not applicable
    The Tolerable Upper Intake Level for selenium is 400 mcg for adults, and it ranges from 45 mcg to 400 mcg for infants, children, and adolescents, depending on age.
    
    Who: adults; infants, children and adolescents 45 to 400 micrograms by age
    Effect: UL 400 micrograms/day for adults; 45 to 400 micrograms/day for infants, children and adolescents by age
    Certainty: A typical "thyroid" dose of 200 mcg + Brazil nuts easily exceeds the UL.
    NIH Office of Dietary Supplements, Selenium Fact Sheet for Health Professionals · checked 2026-10-07 · we read the section
16. ev-selth-16 · Position of an expert body · government fact sheet citing an EFSA scientific opinion · n = not applicable
    Based on systematic reviews that examined associations between excess selenium intake and clinical effects, specifically alopecia, the panel set an upper limit for selenium of 255 mcg/day for all adults, including women who are pregnant or lactating, with lower amounts ranging from 70 to 230 mcg/day for children and teens, depending on age.
    
    Who: all adults including pregnant and lactating women; children and teens 70 to 230 micrograms/day
    Effect: EFSA UL 255 micrograms/day, based on alopecia
    Certainty: Discrepancy between authorities: FNB 400 versus EFSA 255; 200 mcg of supplement + food can exceed the EFSA limit.
    NIH Office of Dietary Supplements, Selenium Fact Sheet for Health Professionals · checked 2026-10-07 · we read the section
17. ev-selth-17 · Meta-analysis or systematic review · Cochrane systematic review of RCTs and observational studies · n = RCTs in Cochrane review CD005195
    RCTs showed a slightly increased risk of type 2 diabetes associated with supplementation.
    
    Who: participants of randomized trials of selenium supplementation (cancer prevention)
    Effect: slightly increased type 2 diabetes risk in RCTs
    Certainty: Data from long prevention RCTs in people well supplied with selenium; for 6-12-month courses in Hashimoto's the risk is unknown.
    Cochrane Database Syst Rev, 2018 · checked 2026-10-07 · we read the abstract
18. ev-selth-18 · Randomized controlled trial(s) · systematic review and meta-analysis of controlled trials, GRADE · n = 16 controlled trials
    Study participants receiving selenium had a significantly higher risk than controls of reporting adverse effects (p = 0.036).
    
    Who: adults with chronic autoimmune thyroiditis, with or without levothyroxine
    Effect: higher risk of reported adverse effects with selenium (p = 0.036); TPOAb WMD -271 at 3 months in LT4-treated; quality of evidence generally low
    Certainty: Contradicts the 2024 meta-analysis (OR 0.89 for adverse effects): a divergence between syntheses.
    Thyroid, 2016 · checked 2026-10-07 · we read the abstract
19. ev-selth-19 · Randomized controlled trial(s) · randomized double-blind placebo-controlled trial · n = 414
    Supplementation with selenium and coenzyme Q10 for 4 years significantly increased fT3 and rT3, decreased fT4, and diminished the increase in TSH levels compared with placebo treatment (p = 0.03, all).
    
    Who: elderly Swedish population with mean plasma selenium 67 micrograms/L (intake about 35 micrograms/day)
    Effect: increased fT3 and rT3, decreased fT4, smaller TSH increase vs placebo (p = 0.03)
    Certainty: Combination with CoQ10; people with selenium deficiency, without thyroid disease. Shows that the effect depends on baseline status.
    BMC Med, 2024 · checked 2026-10-07 · we read the abstract
20. sel-03 · Position of an expert body
    Brazil nuts contain very high amounts of selenium (68–91 mcg per nut) and could cause selenium toxicity if consumed regularly.
    
    Who: general
    Effect: risk of toxicity with regular consumption
    NIH Office of Dietary Supplements, Health Professional Fact Sheet: Selenium · checked 2026-09-16
21. se-d-03 · Laboratory or animal data · gamma and mass spectrometric analysis of trace element content carried out before a randomized trial, on 8 nuts from different batches and 6 samples of nut butter from one batch · n = 8 nuts from 5 batches, 6 butter samples
    In the Brazil nuts, the selenium content ranged from 0.25 to 5.06 µg/g, indicating difficulties to reliably calculate the selenium amount consumed by Brazil nuts.
    
    Who: not applicable, this is a laboratory analysis of food
    Effect: selenium in the nuts ranged from 0.25 to 5.06 micrograms per gram, mean 1.63 with a standard deviation of 0.47; nut butter from one batch ran 3.45 to 3.65 micrograms per gram, mean 3.58 with a standard deviation of 0.07, so the trialists switched to butter and set the dose at 15 g a day
    Certainty: a laboratory measurement on 8 nuts is a small sample and the true spread across the world supply is wider, not narrower, because soil selenium varies by orders of magnitude across the Amazon basin. This is the single most useful fact on the entity for a reader, because the advice that circulates everywhere, one Brazil nut a day covers your needs, is arithmetic done on an average that no individual nut is obliged to match. At the low end of this range a nut delivers about 1 microgram and at the high end about 25 micrograms per gram of nut. A page can say Brazil nuts are the richest plant source and must not turn that into a dose.
    European Journal of Nutrition, 2025 · checked 2026-09-21 · we read the fulltext
22. se-d-08 · Position of an expert body · entries in the EU Register on nutrition and health claims, authorized list · n = 6 authorized selenium claims against 8 non-authorized ones in the same register
    POL-HC-6464 Selenium Selenium contributes to the normal thyroid function Authorised
    
    Who: general population, EU food labeling
    Effect: claim POL-HC-6464, substance Selenium, wording 'Selenium contributes to the normal thyroid function', status Authorised; the other five cover spermatogenesis, hair, nails, immune function and protection of cells from oxidative stress
    Certainty: an authorized claim records that the regulator judged the evidence sufficient for that exact wording, which is a statement about a body function and not about preventing or treating any disease. The register snapshot carries no conditions of use, so the amount a food must contain to make the claim has to come from Regulation (EU) No 432/2012 on EUR-Lex before any of this goes on a page. The contrast with the eight refusals in cards se-d-09 and se-d-10 is the point: the same regulator drew a line, and the line runs between body functions and disease outcomes.
    EU Register on nutrition and health claims (European Commission) · checked 2026-09-21 · we read the dataset