Zinc & selenium and their effect on thyroid health

Dr. Abigail Vermeesch, BCDHH, CNHP, CHS, BS, MS Clinical Nutrition Thyroid & Hashimoto’s 7 min read Medically reviewed July 2026

The thyroid can’t do its job without the right raw materials. Two trace minerals — selenium and zinc — sit quietly behind hormone production and conversion, and a shortfall in either can hold your thyroid back no matter how well the gland itself is working.

Key takeaways

Selenium and zinc are trace minerals essential to thyroid hormone synthesis and to converting T4 into active T3.

The thyroid holds more selenium than any other organ; deficiency is linked to hypothyroidism, Hashimoto’s, goiter, and Graves’.

Zinc is needed to make T3, T4, and TSH — and the relationship is bidirectional, since low thyroid function can also lower zinc.

Test first: correct deficiencies and supplement to optimal without reaching toxicity — needs often rise with an existing thyroid condition.

In this article

I. Nutrients and the thyroid

II. Selenium and thyroid health

III. Zinc and thyroid health

IV. Test first, then supplement

V. Common questions

If you’ve been following us, you know our passion for restoring the health of those who are suffering. In our experience, many of our patients — particularly women — do not have optimal function of the thyroid. You may remember that the thyroid is a butterfly-shaped gland in the lower front of the neck, and its responsibilities reach across the whole body:

Regulating metabolism and body temperature
Supporting heart function and digestion
Muscle control and brain development
Mood regulation and bone maintenance

A number of nutrients contribute to thyroid health. In this article, we’ll focus on two of the most important: selenium and zinc.

Iodine and selenium build T4; a selenium-dependent enzyme (deiodinase) converts stored T4 into active T3 — and zinc is required to make T3, T4, and TSH at all.

Selenium and thyroid health

Selenium is an essential trace element found in the soil, which means the amount in any given food depends on where it was grown.⁵ It is also key to thyroid health — a necessary micronutrient for thyroid hormone synthesis and function. In fact, the concentration of selenium in the thyroid is higher than in any other organ in the body.^1,2

Selenium works together with iodine to activate three different selenium-dependent iodothyronine deiodinases, the enzymes that activate or deactivate thyroid hormones. This process — and selenium itself — is essential for normal growth, development, and metabolism.²

Because of that central role, selenium deficiency is associated with a range of thyroid problems: hypothyroidism, Hashimoto’s, an enlarged thyroid (goiter), thyroid cancer, and Graves’ disease.¹ One study of roughly 1,900 participants found an inverse relationship between serum selenium concentrations and thyroid volume — and a protective effect of selenium against goiter and thyroid-tissue damage.³

Food sources of selenium:

Brazil nuts (by far the richest source)
Seafood — tuna, halibut, sardines, shrimp
Organ meats and eggs
Brown rice, whole grains, and dairy

Recommended daily selenium

Adults (19+)	55 mcg
Pregnancy	60 mcg
Breastfeeding	70 mcg
Tolerable upper limit	400 mcg

Amounts from the NIH Office of Dietary Supplements.⁵

Please note: with an existing thyroid condition, the amount your body needs is often higher than these general recommendations — which is why dosing should be individualized.

Selenium’s reach extends to autoimmune thyroid eye disease, too. In one study of Graves’ orbitopathy — thyroid eye disease driven by an overactive thyroid — researchers compared selenium to pentoxifylline, an anti-inflammatory. The selenium group reported an improved quality of life, reduced ocular involvement, and slowed progression of Graves’ orbitopathy compared with the pentoxifylline group.⁴

Zinc and thyroid health

Zinc is another trace element that is essential for growth, development, and a healthy immune system, with a major impact on the nervous and reproductive systems as well.⁶

Where the thyroid is concerned, zinc is needed for the synthesis of thyroid hormones — specifically the production of T3, T4, and thyroid stimulating hormone (TSH). A deficiency in zinc can lead to hypothyroidism. And the relationship runs both ways: hypothyroidism can itself lead to a zinc deficiency, because thyroid hormones are required for the absorption of zinc.⁷

Food sources of zinc:

Meat (beef, lamb, pork) and shellfish (oysters are richest)
Legumes, and hemp, pumpkin, squash & sesame seeds
Pine nuts, peanuts, cashews, almonds, and eggs
Whole grains, potatoes, green beans, kale, dark chocolate, dairy

Recommended daily zinc

Adult women	8 mg
Adult men	11 mg
Pregnancy	11 mg
Breastfeeding	12 mg
Tolerable upper limit	40 mg

Amounts from the NIH Office of Dietary Supplements.¹⁰

Please note: as with selenium, an existing thyroid condition often raises the amount of zinc your body needs above these general recommendations.

The research bears this out. In a case study of two college-aged women who were zinc deficient, researchers asked them to supplement with zinc for four months. By the end, both women showed improvement across all thyroid levels — especially T3 — as well as in resting metabolic rate.⁸ A separate randomized study found that taking zinc alone, or in combination with selenium, can improve thyroid function in women with hypothyroidism.⁹

Test first, then supplement

Here’s where our approach matters. Both selenium and zinc are essential — but both can also become harmful in excess, so more is not better. For optimal thyroid health, we recommend testing your levels of these important trace elements before supplementing.

Correct the deficiency, supplement to optimal — without ever moving into toxic levels.

We’ll work with you to address deficiencies and supplement adequately. Getting your selenium and zinc into an optimal range supports your thyroid — and your overall health and wellness along with it.

Nutrient status is only one piece of the thyroid picture. If you haven’t had a full workup, start with the 9 thyroid tests you need to know, and see how the gut affects nutrient absorption and hormone conversion in could your thyroid be the cause of your digestive woes?

Keep reading: Get the full thyroid workup in 9 thyroid tests you need to know, see how gut health shapes nutrient absorption in could your thyroid be the cause of your digestive woes?, and learn the diet connection in why ditching gluten and dairy may help autoimmune thyroid disease. Or explore how we help with thyroid & Hashimoto’s.

Common questions

Why are selenium and zinc important for thyroid health?

Both are trace minerals the thyroid depends on. Selenium is required for thyroid hormone synthesis and, with iodine, activates the deiodinase enzymes that convert thyroid hormones between their active and inactive forms. Zinc is needed to produce T3, T4, and TSH. Deficiency in either is associated with impaired thyroid function.

Can low selenium or zinc cause hypothyroidism?

Low levels of either mineral are associated with reduced thyroid function. Selenium deficiency is linked to hypothyroidism, Hashimoto's, goiter, and Graves' disease, and a zinc deficiency can lead to hypothyroidism. The relationship with zinc runs both ways — hypothyroidism can also lower zinc, because thyroid hormones are needed to absorb it.

What foods are highest in selenium and zinc?

Selenium is found in Brazil nuts (by far the richest source), seafood, organ meats, eggs, and whole grains, though soil content varies by region. Zinc is found in meat, shellfish (oysters are especially rich), legumes, seeds, nuts, eggs, whole grains, and dairy.

Should I take selenium and zinc supplements for my thyroid?

We recommend testing your levels first. The goal is to correct any deficiency and supplement to an optimal level without reaching toxicity, since both minerals can be harmful in excess. Needs are often higher when a thyroid condition is already present, so dosing should be personalized with a practitioner.

References (10) ▾

Ventura M, Melo M, Carrilho F. Selenium and thyroid disease: from pathophysiology to treatment. Int J Endocrinol. 2017;2017:1297658. https://pubmed.ncbi.nlm.nih.gov/28255299/
Köhrle J. Selenium and the thyroid. Curr Opin Endocrinol Diabetes Obes. 2015;22(5):392-401. https://pubmed.ncbi.nlm.nih.gov/26313901/
Derumeaux H, Valeix P, Castetbon K, et al. Association of selenium with thyroid volume and echostructure in 35- to 60-year-old French adults. Eur J Endocrinol. 2003;148(3):309-315. https://pubmed.ncbi.nlm.nih.gov/12611611/
Marcocci C, Kahaly GJ, Krassas GE, et al. Selenium and the course of mild Graves’ orbitopathy. N Engl J Med. 2011;364(20):1920-1931. https://pubmed.ncbi.nlm.nih.gov/21591944/
National Institutes of Health, Office of Dietary Supplements. Selenium: fact sheet for health professionals. https://ods.od.nih.gov/factsheets/Selenium-HealthProfessional/
Roohani N, Hurrell R, Kelishadi R, Schulin R. Zinc and its importance for human health: an integrative review. J Res Med Sci. 2013;18(2):144-157. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3746228/
Severo JS, Morais JBS, de Freitas TEC, et al. The role of zinc in thyroid hormones metabolism. Int J Vitam Nutr Res. 2019;89(1-2):80-88. https://pubmed.ncbi.nlm.nih.gov/30982439/
Maxwell C, Volpe SL. Effect of zinc supplementation on thyroid hormone function: a case study of two college females. Ann Nutr Metab. 2007;51(2):188-194. https://pubmed.ncbi.nlm.nih.gov/17541266/
Mahmoodianfard S, Vafa M, Golgiri F, et al. Effects of zinc and selenium supplementation on thyroid function in overweight and obese hypothyroid female patients: a randomized double-blind controlled trial. J Am Coll Nutr. 2015;34(5):391-399. https://pubmed.ncbi.nlm.nih.gov/25758370/
National Institutes of Health, Office of Dietary Supplements. Zinc: fact sheet for health professionals. https://ods.od.nih.gov/factsheets/Zinc-HealthProfessional/

This article is educational and is not medical advice, diagnosis, or treatment. Supplements and therapeutic doses should be personalized with a qualified practitioner — both selenium and zinc can be harmful in excess.

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