Selenium

Selenium supplementation · Selenomethionine

Snapshot

Indications	Contraindications
Hashimoto thyroiditis^{1, 2} Selenium deficiency³ Keshan disease prevention³ Graves orbitopathy⁴ Male infertility, sperm motility^{5, 6} Depressive symptoms⁷ Rheumatoid arthritis joint pain⁸	Thyroid autoimmunity in pregnancy³ Selenium-replete prostate risk³ Doses above upper limit³

Selenium is an essential mineral that is a constituent of 25 selenoproteins, which support thyroid hormone metabolism, DNA synthesis, reproduction, and protection from oxidative damage³. Supplementation is used in autoimmune thyroid disease, where a meta-analysis of trials in Hashimoto thyroiditis found it lowered thyroid peroxidase antibodies and thyroid-stimulating hormone levels². People in low-selenium regions, vegetarian and vegan eaters, and patients after bariatric surgery carry the highest risk of inadequate status³.

For cancer and cardiovascular prevention, a Cochrane review and ODS found no benefit in selenium-replete adults, and an umbrella review advised against routine supplementation in general populations³. In children with drug-resistant epilepsy, a 2026 meta-analysis of observational studies found lower serum selenium than in healthy controls; no trial has tested supplementation there⁹. Supplements come as selenomethionine, selenium-enriched yeast, sodium selenite, and sodium selenate; see Form comparison³.

The narrow margin matters most: chronic excess causes hair and nail loss, and a 2026 dose-response meta-analysis linked higher doses to adverse blood lipid changes³. Per the American Thyroid Association, selenium is not recommended in pregnant women with thyroid autoimmunity, and MSKCC states supplementation during cancer treatment belongs under practitioner guidance^{3, 10}.

Last updated October 16, 2026. Read how we make monographs.

In the full monograph

81 sources, 69 studies

When to useThe situations practitioners use it for, each with the reason and the study behind it.
SafetyWho should avoid it, who needs extra care, and the side effects reported in studies.
InteractionsThe medicines and supplements it interacts with, the effect of each, and what labeling says to watch.
Protocol notesThe doses used in studies, how and when they were taken, and how the forms on the market compare.
How it worksWhat it is and how it works in the body, in plain terms.
Published studiesThe studies behind each use, popular claims checked against them, and trials still under way.
Word of mouthWhat patients and practitioners report online, kept separate from the clinical evidence.
Clinical perspectiveA closing read of where the evidence is solid, where it is thin, and what has not been studied.

Snapshot

In the full monograph

Sources