Selenium
Selenium is an essential mineral that is naturally present in many foods and added to others. In foods, selenium is present primarily as selenomethionine along with selenocysteine. Selenium deficiency is very rare in the United States and Canada.
Where to get it
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Active compounds & mechanisms
Key compounds: Selenomethionine, Selenocysteine
Selenium plays important roles in the synthesis and metabolism of thyroid hormones.
Research & evidence
Strong support Some support Weak or no supportColours show how well the sources back each point. The reason is next to each one.
NIH says epidemiological studies have found associations between low selenium status and an increased risk of thyroid disease.
Limited evidenceSome support. Reviewers rated the certainty low
Study details
NIH ODS: "Selenium plays important roles in the synthesis and metabolism of thyroid hormones." "Epidemiological studies have found associations between low selenium status and an increased risk of thyroid disease."
Source: NIH ODS, Selenium — Health Professional Fact Sheet, Selenium and Health (thyroid) View source
NIH says more research is needed to characterize the relationship between selenium supplementation and cancer risk. The authors NIH describes found no association between selenium status in women and the risk of breast cancer, and no evidence of a dose-response relationship between selenium status and cancer risk was observed.
Limited evidenceSome support. Reviewers rated the certainty low
Study details
NIH ODS: "More research is needed to characterize the relationship between selenium supplementation and cancer risk." "The authors found no association between selenium status in women and the risk of breast cancer." "In addition, no evidence of a dose-response relationship between selenium status and cancer risk was observed."
Source: NIH ODS, Selenium — Health Professional Fact Sheet, Selenium and Health (cancer) View source
NIH says results from early observational studies suggested that low selenium status might increase the risk of cardiovascular disease, but epidemiological studies since then have yielded conflicting findings.
Mixed evidenceSome support. Results are mixed
Study details
NIH ODS: "Results from early observational studies suggested that low selenium status might increase the risk of CVD." "Since then, epidemiological studies on the role of selenium in CVD have yielded conflicting findings."
Source: NIH ODS, Selenium — Health Professional Fact Sheet, Selenium and Health (cardiovascular disease) View source
NIH says randomized trials suggest that selenium supplementation has little effect on HIV disease progression or treatment.
Limited evidenceSome support. The source hedges (“may” or “associated with”)
Study details
NIH ODS: "However, randomized trials suggest that selenium supplementation has little effect on HIV disease progression or treatment."
Source: NIH ODS, Selenium — Health Professional Fact Sheet, Groups at Risk of Selenium Inadequacy View source
Dosage
| Form | Amount |
|---|---|
| Any form | No standard dose is listed by our sources. |
Side effects
Well documented Reported (case reports, anecdotal or one study) None reportedThe circle shows how well documented an effect is, not how serious it is. A rarely reported effect can still be serious, so always read ‘When to stop’.
| Effect | Frequency | When to stop |
|---|---|---|
| Garlic odor on the breath and a metallic taste in the mouth (early signs of excess selenium)Well documentedListed plainly by NIH, MSK or LiverTox | With chronically high intakes | Stop and talk to a doctor if you notice any unexpected or concerning symptoms. |
| Skin rash, nausea, diarrhea, fatigue, irritability, and nervous system abnormalities (with excess selenium)Well documentedListed plainly by NIH, MSK or LiverTox | With chronically high intakes | Stop and talk to a doctor if you notice any unexpected or concerning symptoms. |
Safety & interactions
Safety
Selenosis is the result of chronically high intakes of selenium. Chronically high intakes of the organic and inorganic forms of selenium have similar effects. Early indicators of excess intake are a garlic odor in the breath and a metallic taste in the mouth. Other signs and symptoms include skin rash, nausea, diarrhea, fatigue, irritability, and nervous system abnormalities. Selenium supplements may interact with medications.
Contraindications
The American Thyroid Association recommends against selenium supplementation in pregnant women who have thyroid autoimmunity. Selenosis, the result of chronically high intakes of selenium, can cause the signs listed under Safety and Side effects. See Drug interactions.
Drug interactions
NIH says selenium supplements may interact with medications, and that certain medications, such as cisplatin, can affect selenium levels in the body. NIH describes cisplatin as an inorganic platinum chemotherapy agent used to treat ovarian, bladder, lung, and other cancers.
Established: stated plainly by an authoritative source. Documented: supported by case reports or trial data. Theoretical: based on mechanism, animal data, or a cautious listing. Always check with your pharmacist or prescriber.
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