Selenium and Hashimoto's: Do Supplements Work?

Short Answer

Selenium supplements can lower anti-TPO antibodies in Hashimoto's, but this has not been shown to change the course of the disease. According to the TEMD 2025 guideline, there are insufficient data that it prevents hypothyroidism; routine use is not recommended. Selenium has a narrow safety margin: according to EFSA 2023, the adult upper limit is 255 µg a day. Selenium is not a substitute for thyroid medication.

What does it do?

Selenium is part of the structure of proteins in the body called "selenoproteins." According to TEMD 2025, the thyroid gland is rich in selenium. Selenoproteins neutralize the hydrogen peroxide formed during thyroid hormone production. They also help convert T4 into the active hormone T3.

So the correct statement about selenium is: "it contributes to normal thyroid function and to the protection of cells from oxidative stress." Selenium does not treat Hashimoto's. It is not a substitute for thyroid drugs such as levothyroxine.

Daily requirement

The requirement varies by age and breastfeeding status. The values are for healthy people.

Group	Daily selenium	Source
Adult (Türkiye)	70 µg	TÜBER 2022
Pregnant (Türkiye)	70 µg	TÜBER 2022
Breastfeeding (Türkiye)	85 µg	TÜBER 2022
Adult (US)	55 µg	NIH ODS (IOM)
Pregnant / breastfeeding (US)	60 µg / 70 µg	NIH ODS (IOM)

The gap between the requirement and the upper limit is small. TEMD 2025 also stresses that selenium's safety range is narrow.

Which foods contain it?

According to TEMD 2025, the main sources are seafood, eggs, bread and cereals, dairy products, nuts and meat. TÜBER 2022 (the Turkish Ministry of Health's Türkiye Nutrition Guide) also lists meat and other animal products, organ meats, seafood and garlic as sources of selenium. An adult with a varied diet usually meets their requirement from these foods.

Brazil nut warning: According to NIH, a single Brazil nut can contain 68–91 µg of selenium. So even a few can bring you close to the upper limit. EFSA notes that people who regularly eat Brazil nuts may exceed the upper limit. Selenium in plant foods varies greatly depending on the selenium content of the soil.

Who is at risk of deficiency?

According to NIH, selenium deficiency alone rarely causes disease in healthy people with a varied diet. The risk increases in the following groups:

• Kidney patients on dialysis
• People living with HIV
• People who eat only local produce in regions with selenium-poor soil

Symptoms are not distinctive. According to TEMD 2025, selenium deficiency can impair thyroid hormone production and the conversion of T4 to T3. This can contribute to goiter and thyroid damage.

Which test, and how is it read?

Selenium can be measured in the blood, but this is not a routine screening test. The result reflects recent intake and varies with the laboratory method. Your doctor may order it in the following situations:

• If symptoms persist despite thyroid treatment (TEMD 2025 recommends monitoring iron, iodine and selenium status in this case)
• If there is malabsorption, dialysis or a long-term nutritional problem
• If you are using high-dose supplements and show signs of toxicity

Hashimoto's is not diagnosed or monitored with a selenium test. TSH, free T4 and anti-TPO are used for this. For details, see the thyroid tests guide.

When is a supplement needed, and when not?

Evidence in Hashimoto's:

• Cochrane 2013: 4 randomized trials and 463 people were reviewed. Selenium was seen to lower anti-TPO, but the clinical significance remained unclear. According to the authors, evidence was lacking to support or refute its effectiveness.
• Thyroid 2024 meta-analysis: 35 randomized trials were evaluated. In people not taking thyroid medication, TSH fell slightly. Anti-TPO decreased in both those taking and not taking medication, but the differences between studies were large. Anti-Tg and free T4 did not change. Progression to hypothyroidism was not examined in this analysis.
• TEMD 2025: A clinical effect of the antibody decrease has not been shown. There are insufficient data that it prevents hypothyroidism; routine use is not recommended.

In short, a fall in the anti-TPO value does not mean the course of the disease has changed. The main treatment in Hashimoto's is thyroid hormone, if needed.

Mild Graves' eye disease: TEMD 2025 recommends 6 months of selenium treatment in recent-onset, mild and active Graves' orbitopathy (moderate-level evidence). According to the guideline, its effect in regions without selenium deficiency is unknown. This decision belongs to the endocrinologist and the ophthalmologist.

Situations where it is not needed: A person with normal thyroid function and a varied diet does not need selenium to "protect the thyroid." TEMD 2025 stresses that most popular approaches on social media have no clear evidence-based benefit.

Upper limit and excess

Upper limits according to the EFSA 2023 opinion:

Age group	Daily upper limit	Source
Adult (including pregnant and breastfeeding)	255 µg	EFSA 2023
Ages 15–17	230 µg	EFSA 2023
Ages 11–14	180 µg	EFSA 2023
Ages 7–10	130 µg	EFSA 2023
Ages 1–3 / ages 4–6	70 µg / 95 µg	EFSA 2023

How was the limit set? EFSA used hair loss as the early and distinct sign of excess selenium. In the SELECT trial, hair loss and skin findings increased in people taking a total of about 330 µg/day from food and supplements. This value was divided by 1.3 to set the adult limit. In the US, the upper limit set by the IOM is 400 µg a day; NIH still gives this limit as the current value.

Symptoms of selenosis (selenium toxicity): According to NIH, a garlic odor on the breath and a metallic taste in the mouth are early signs. Later, hair and nail loss, brittle nails, skin rash, fatigue and nervous system disorders can occur. NIH reports that in 2008 a supplement containing about 200 times the selenium stated on its label caused poisonings.

Diabetes signal: According to TEMD 2025, there are data that excessive selenium levels increase the risk of type 2 diabetes.

The hidden total: Selenium can add up from multivitamins, "thyroid support" blends, hair-and-nail products and Brazil nuts. Add up the µg values on the labels.

Drug and test interactions

Selenium has few drug interactions of high clinical significance. According to NIH, the chemotherapy drug cisplatin can lower selenium levels; the benefit of supplementation in this situation has not been proven.

• Selenium is not a reason to change the dose of your thyroid medication. Do not reduce or stop your medication on your own.
• "Thyroid support" products may also contain iodine and sometimes biotin. Biotin can interfere with thyroid tests. For details, see the biotin and lab tests guide.
• Tell your doctor or pharmacist about all the supplements you use.

In Türkiye

• National guideline: The TEMD Thyroid Diseases Diagnosis and Treatment Guideline 2025 states that selenium can lower antibodies in Hashimoto's but that its clinical benefit has not been shown. It does not recommend routine use.
• Reference values: The Turkish Ministry of Health's TÜBER 2022 guide gives the adult upper limit as 300 µg. The limit set by EFSA in 2023, however, is 255 µg. Use the newer and lower EFSA limit.
• Supplement approval: The Ministry of Agriculture and Forestry approves each food supplement individually. Check whether a product is approved in the list on GGBS. You can report unsuitable products to the Alo 174 Food Line.
• Label: In products called "thyroid support," check the amounts of selenium, iodine and biotin separately. For details, see the guide how to read a supplement label.

Which doctor should you see?

• Hashimoto's diagnosis or positive anti-TPO: Endocrinology or Internal Medicine.
• Eye swelling, grittiness or double vision in Graves' disease: Endocrinology and Ophthalmology.
• Hair or nail loss together with selenium use: Dermatology or Internal Medicine.
• Bring with you: Supplement boxes, your latest TSH, free T4 and anti-TPO results, and your medication list.

When should you seek emergency care?

• If a child has swallowed an iron-containing product, call 112 (the emergency number in Türkiye) without waiting for symptoms. If they swallowed another supplement, call the 114 National Poison Information Center; if there is drowsiness, vomiting, breathing difficulty or a seizure, call 112.
• Severe vomiting, diarrhea or a garlic odor on the breath after high-dose selenium: call 114. If there is clouding of consciousness, breathing difficulty or a seizure, call 112.
• Sudden vision loss or seeing colors as faded in Graves' disease: go immediately to the emergency department or an eye emergency service.
• Very rapid palpitations, high fever and agitation: this may be a thyroid storm; call 112.
• A rapidly growing swelling in the neck or difficulty swallowing: go to the emergency department without delay. If there is shortness of breath, call 112.

Related guides

• Vitamin and Mineral Guide
• Supplement check tool
• Thyroid diseases and Hashimoto's guide
• Iodine deficiency and iodized salt
• What do TSH test results mean?
• Supplement-drug interactions

What changed? (October 2026)

• The adult upper limit was given as 255 µg according to the EFSA 2023 opinion.
• The Hashimoto's evidence was updated with Cochrane 2013, the Thyroid 2024 meta-analysis and the TEMD 2025 guideline.
• Türkiye reference values were given according to TÜBER 2022. Emergency guidance was updated.

Sources

• Türkiye Endokrinoloji ve Metabolizma Derneği. Tiroid Hastalıkları Tanı ve Tedavi Kılavuzu 2025. https://file.temd.org.tr/Uploads/publications/guides/documents/tiroid2025_11042025.pdf (accessed October 4, 2026)
• Sağlık Bakanlığı. Türkiye Beslenme Rehberi (TÜBER) 2022. https://hsgm.saglik.gov.tr/depo/birimler/saglikli-beslenme-ve-hareketli-hayat-db/Dokumanlar/Rehberler/Turkiye_Beslenme_Rehber_TUBER_2022_min.pdf (accessed October 4, 2026)
• T.C. Tarım ve Orman Bakanlığı, Güvenilir Gıda. Bir takviye edici gıdanın onaylı olup olmadığını nereden öğrenebiliriz? February 10, 2026. https://guvenilirgida.tarimorman.gov.tr/Haber/Detay/17314 (accessed October 4, 2026)
• EFSA NDA Panel. Scientific opinion on the tolerable upper intake level for selenium. EFSA Journal 2023;21(1):7704. https://doi.org/10.2903/j.efsa.2023.7704 (accessed October 4, 2026)
• EFSA. Overview on Tolerable Upper Intake Levels as derived by the SCF and the EFSA NDA Panel. Version 11, August 2025. https://www.efsa.europa.eu/sites/default/files/2024-05/ul-summary-report.pdf (accessed October 4, 2026)
• NIH Office of Dietary Supplements. Selenium: Fact Sheet for Health Professionals. Updated September 4, 2025. https://ods.od.nih.gov/factsheets/Selenium-HealthProfessional/ (accessed October 4, 2026)
• van Zuuren EJ, Albusta AY, Fedorowicz Z, Carter B, Pijl H. Selenium supplementation for Hashimoto's thyroiditis. Cochrane Database Syst Rev 2013;(6):CD010223. https://www.cochrane.org/evidence/CD010223_selenium-supplementation-hashimotos-thyroiditis (accessed October 4, 2026)
• Huwiler VV et al. Selenium Supplementation in Patients with Hashimoto Thyroiditis: A Systematic Review and Meta-Analysis of Randomized Clinical Trials. Thyroid 2024;34(3):295-313. https://doi.org/10.1089/thy.2023.0556 (accessed October 4, 2026)