Mineral supplements. Trace elements
ATC code: A12CE-SELENIUM (Selenium (oral salts and chelates, generic group))
Brand names – supplements
Thorne Selenomethionine, Pure Encapsulations Selenium, Life Extension Super Selenium Complex
Supplements are not tested in clinical trials and are not registered as medications.
Selenium is a component of selenoproteins (more than 25 identified in humans), including glutathione peroxidases (antioxidant defence), iodothyronine deiodinases (thyroid hormone conversion from T4 to T3), and thioredoxin reductases (redox regulation). An essential trace element. Soil and food selenium content varies markedly by geography: eastern Siberia, north-western regions of Russia, and north-eastern China are low-selenium regions.
First line
Selenium preparations are first-line for confirmed selenium deficiency. Treatment dose: 100–200 µg elemental selenium daily for 1–3 months with plasma selenium monitoring. In residents of regions with low soil selenium (eastern Siberia, north-western Russia), supplementation at the RDA is reasonable on a varied diet but not mandatory. In patients on long-term parenteral nutrition, daily supplementation of 60–100 µg is standard.
Adjunct
Selenomethionine 100 µg twice daily for 6 months in patients with mild-to-moderate active thyroid eye disease showed improved quality of life and slowed disease progression in the NEJM 2011 RCT (159 patients). 2021 included selenium in mild Graves orbitopathy recommendations as a level A evidence agent. The effect is more pronounced in Europe (a low-selenium soil region); in the US and Japan the effect was smaller.
Use is justified only in the active phase of mild disease. In severe or sight-threatening disease: glucocorticoids, teprotumumab, orbital decompression.
Individual decision
The 2013 Cochrane review showed a moderate reduction in TPO antibody titres with selenomethionine 200 µg daily in autoimmune thyroiditis. The clinical significance of antibody titre reduction is debated – long-term effects on progression to hypothyroidism, levothyroxine dose, or symptoms have not been confirmed in large RCTs. Russian endocrinology guidelines 2021 do not include selenium as first-line in Hashimoto thyroiditis. The decision is individualised.
Not recommended
— Anti-aging and longevity: Selenium for slowing ageing or extending lifespan in non-deficient individuals is not mentioned in international guidelines. The antioxidant ageing hypothesis underlying this marketing argument has not received compelling clinical support. Long-term high-dose selenium is dangerous due to selenosis.
Not recommended
The large SELECT RCT (35,533 men, 7 years of follow-up, JAMA 2009) showed no protective effect of selenium 200 µg and vitamin E 400 IU daily on prostate or other cancers. In a subset of patients, prostate cancer risk increased in the selenium arm. Cochrane 2018 confirmed no effect of selenium on cancer prevention or all-cause mortality in non-selenium-deficient people. Selenium for cancer prevention is not supported by international guidelines.
Safe at physiological doses (60 µg daily). Doses above 200 µg daily in pregnancy are not recommended. In pregnant women with confirmed deficiency, supplementation is monitored by plasma levels.
Actively secreted into breast milk. Maternal supplementation at physiological doses is safe and increases milk selenium in deficient mothers.
selenium (oral salts and chelates: selenomethionine, sodium selenite, selenium yeast) is evaluated for the following indications with varying evidence strength: Selenium deficiency (evidence tier A), Graves orbitopathy (thyroid eye disease) (evidence tier B), Hashimoto thyroiditis (chronic autoimmune thyroiditis) (evidence tier C). See the full indication matrix with dosing and citations above on this page.
Common side effects of selenium (oral salts and chelates: selenomethionine, sodium selenite, selenium yeast) (≥ 1 in 100): Garlic breath at doses above 400 µg daily, Nausea, epigastric discomfort, Metallic taste. See the Safety section for uncommon and serious reactions.
FDA category C. Safe at physiological doses (60 µg daily). Doses above 200 µg daily in pregnancy are not recommended. In pregnant women with confirmed deficiency, supplementation is monitored by plasma levels.
Actively secreted into breast milk. Maternal supplementation at physiological doses is safe and increases milk selenium in deficient mothers.
selenium (oral salts and chelates: selenomethionine, sodium selenite, selenium yeast) is contraindicated in: Hypersensitivity to selenium; Selenosis (any signs of overdose); Pregnancy and breastfeeding at doses above the RDA. Full list in the Safety section.
the SELECT RCT (over 35,000 men) did not confirm a protective effect; in a subgroup selenium increased prostate cancer risk. Cochrane 2018: no effect on cancer incidence.
the effect on AIT antibody titre reduction is modest, on clinical outcomes – not proven. In patients without confirmed selenium deficiency and without AIT, supplementation is unjustified.
in non-deficient people, the effect is not proven. Selenium in excess is toxic – doses above 400 µg daily long-term cause selenosis. The safety window between the RDA (55 µg) and toxic doses is narrow.