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Selenium

Also known as: selenomethionine, sodium selenite

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Selenium is an essential trace mineral important for antioxidant defense and thyroid function. A little goes a long way — the gap between a helpful dose and too much is narrow, so the upper limit matters.

What it is

A trace mineral and component of selenoproteins (like glutathione peroxidase) that protect cells from oxidative damage and are required for thyroid hormone metabolism. The thyroid holds the body's highest selenium concentration.1

Commonly used for

Thyroid (autoimmune): in Hashimoto's thyroiditis, supplementation has been shown to lower thyroid antibodies (TPOAb) and TSH and reduce oxidative-stress markers; doses of 80–400 mcg/day for up to 12 months appear safe and effective for this use.2

Antioxidant: supports general antioxidant capacity.1

Typical dosing

RDA is 55 mcg/day for adults. Supplements typically provide 100–200 mcg/day; thyroid studies commonly use 200 mcg/day (often as selenomethionine). The Tolerable Upper Intake Level is 400 mcg/day — do not exceed without medical supervision.12

Route of administration

Oral, as tablets or capsules (commonly selenomethionine or sodium selenite); also obtained from food, notably Brazil nuts.

Storage & handling

Store at room temperature, away from heat, light, and moisture.

Common considerations

Excess selenium (selenosis) causes hair/nail loss, garlic breath, GI upset, and at extreme doses serious toxicity. Note: just one Brazil nut can contain ~95 mcg. Some long-term trials noted a possible increase in type 2 diabetes risk in already-replete people. Relevant if you take thyroid medication — discuss with your provider.

References

  1. 1. NIH Office of Dietary Supplements — Selenium Fact Sheet for Health Professionals Fact sheet
  2. 2. Huwiler VV, et al. — Selenium Supplementation in Patients with Hashimoto Thyroiditis: A Systematic Review and Meta-Analysis of Randomized Clinical Trials (Thyroid, 2024) Systematic review

The information on this page is provided for general educational purposes only. It is not medical advice and is not a substitute for consultation with a qualified healthcare provider. Individual needs, contraindications, and responses to supplementation vary, and decisions about starting, stopping, or modifying any supplement or medication should be made in consultation with a physician, pharmacist, or other appropriate professional. References are provided to authoritative sources; STACK Tracker does not endorse any specific product or brand.