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Selenium Side Effects & Safety

Evidence:Moderate
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This content is for informational purposes only and does not constitute medical advice. Statements about dietary supplements have not been evaluated by the FDA and are not intended to diagnose, treat, cure, or prevent any disease. Individual results may vary — consult your healthcare provider before starting any supplement. Full disclaimer

Safety Profile

Overall safety rating: Generally Safe

Potential Side Effects

  • Garlic breath odor at higher doses
  • Nausea and diarrhea (uncommon at recommended doses)
  • Selenosis at chronic doses >400mcg/day: hair loss, nail brittleness, fatigue, irritability
  • Possible increased type 2 diabetes risk at high doses (>200mcg/day) per SELECT trial data

Drug & Supplement Interactions

  • May enhance the anticoagulant effect of warfarin
  • Cisplatin and other chemotherapy drugs — selenium may alter drug metabolism
  • Statins — selenium may have additive cholesterol-lowering effects
  • Vitamin C taken simultaneously may reduce selenium absorption — separate by 30 minutes

Maximum Dose

Do not exceed: 400mcg/day (NIH UL); chronic intake above this causes selenosis

Full Selenium Guide

References

  1. RCTLippman SM, Klein EA, Goodman PJ, et al. (2009). Effect of selenium and vitamin E on risk of prostate cancer and other cancers: the Selenium and Vitamin E Cancer Prevention Trial (SELECT). JAMA. DOI PubMed
  2. Meta-analysisWichman J, Winther KH, Bonnema SJ, Hegedus L (2016). Selenium supplementation significantly reduces thyroid autoantibody levels in patients with chronic autoimmune thyroiditis: a systematic review and meta-analysis. Thyroid. DOI PubMed
  3. RCTThomson CD, Chisholm A, McLachlan SK, Campbell JM (2008). Brazil nuts: an effective way to improve selenium status. American Journal of Clinical Nutrition. DOI PubMed
  4. Meta-analysisHuwiler VV, Maissen-Abgottspon S, Stanga Z, Mühlebach S, et al. (2024). Selenium Supplementation in Patients with Hashimoto Thyroiditis: A Systematic Review and Meta-Analysis of Randomized Clinical Trials.. Thyroid : official journal of the American Thyroid Association. DOI PubMed
  5. Meta-analysisSharabati I, Qafesha RM, Hindawi MD, Amro S, et al. (2024). The efficacy and safety of selenium supplementation versus placebo in the treatment of Graves' orbitopathy: A systematic review and meta-analysis of randomised controlled trials.. Clinical endocrinology. DOI PubMed
  6. Zhou J, Zhang W, Cao Z, Lian S, et al. (2023). Association of Selenium Levels with Neurodegenerative Disease: A Systemic Review and Meta-Analysis.. Nutrients. DOI PubMed
  7. Filippini T, Fairweather-Tait S, Vinceti M (2023). Selenium and immune function: a systematic review and meta-analysis of experimental human studies.. The American journal of clinical nutrition. DOI PubMed
Show 3 more references
  1. Ding J, Zhang Y (2022). Relationship between the Circulating Selenium Level and Stroke: A Meta-Analysis of Observational Studies.. Journal of the American Nutrition Association. DOI PubMed
  2. Lv J, Ai P, Lei S, Zhou F, et al. (2020). Selenium levels and skin diseases: systematic review and meta-analysis.. Journal of trace elements in medicine and biology : organ of the Society for Minerals and Trace Elements (GMS). DOI PubMed
  3. Vinceti M, Filippini T, Del Giovane C, Dennert G, et al. (2018). Selenium for preventing cancer.. The Cochrane database of systematic reviews. DOI PubMed