Written by Gabriele Dennert and the CAM-Cancer Consortium.
Updated October 20, 2013

Selenium – during cancer treatment

Is it safe?

Adverse events

Early signs of selenium toxicity (garlic breath, hair and nail changes, upset stomach) were observed in participants of a clinical trial who received 1600µg or 3200µg selenised yeast/day for up to 24 months. 24 In the Selenium and Vitamin E Cancer Prevention Trial, 25 which used 200 µg/day selenomethionine for 7–12 years, the rate of alopecia (overall incidence: 3% of participants) and mild dermatitis (7% of participants) was higher than in the placebo group (relative risk increase: +28% and +17%, respectively). Neither trial reported more severe adverse effects or signs of chronic toxicity.

Chronic selenium poisoning (selenosis) has been seen in seleniferous areas of North America and China, but has also been attributed to commercially available selenium supplements. 24 Symptoms of selenosis include hair loss, thickened nails, nausea, vomiting, fatigue and paresthesia and paralysis. The EU Scientific Committee on Food considers an upper selenium limit (for adults) of 300µg/day (including supplements) to be acceptable for the avoidance of selenosis. 26 The US Food and Nutrition Board, Institute of Medicine, have set the tolerable upper level of selenium intake to 400µg/day. 3

However, there are concerns that long-term selenium supplementation may increase the risk of developing type 2 diabetes mellitus in selenium-replete populations. The relative risk for male selenium users in the SELECT trial was 1.07 (95% confidence interval (CI) 0.94–1.22), when compared to the placebo group; this meant that there were six additional cases of diabetes in every 1000 selenium users per year (diabetes risk: +7% in the selenium group compared to placebo). 25 In the Nutritional Prevention of Cancer Trial (NPCT), the risk of developing diabetes mellitus in the selenium group was 1.55 (95% CI: 1.03–2.33); this meant that there were four additional cases of diabetes in 1000 selenium users per year (diabetes risk: +55% in the selenium group). 27

Lethal and non-lethal acute poisoning related to use of selenium as a complementary alternative medicine has been reported in a number of cases. 28,29 The lethal dose of selenium in humans is unknown, but is estimated to be between 0.12g and 1g (120–1000mg). 26 Acute poisoning is characterised by vomiting, garlic breath, abdominal pain, hypersalivation, cardiac arrhythmia, haemolysis, necrosis of the liver, cerebral and pulmonary oedema, coma and death. 30


Chronic overexposure to selenium (selenosis).

According to the NPCT, selenium may increase the risk of non-melanoma cancer recurrenceSelenium supplementation may therefore be problematic, especially for light-skinned people. 31


Vitamin C can lower the intestinal absorption of selenium. 32

Other problems or complications

Severe complications have been reported because not only consumers, but also healthcare professionals, have confused the measurements ‘milligram’ (mg) and ‘microgram’ (µg). Also, a number of websites mistakenly recommend ‘milligrams’ of selenium instead of ‘micrograms’, the ingestion of which may result in a thousand-fold overdose.

No controlled data are available on the effects of selenium supplements in non-selenium-deficient women during pregnancy or lactation.

Citation Gabriele Dennert, CAM-Cancer Consortium. Selenium – during cancer treatment [online document]. http://ws.cam-cancer.org/The-Summaries/Dietary-approaches/Selenium-during-cancer-treatment. October 20, 2013.


  1. Rayman MP, Infante HG, Sargent M. Food-chain selenium and human health: spotlight on speciation. Br J Nutr 2008; 100: 238-53.
  2. Rayman MP. The use of high-selenium yeast to raise selenium status: how does it measure up? Br J Nutr 2004; 92(4): 557-73.
  3. http://iom.edu/Activities/Nutrition/SummaryDRIs/~/media/Files/Activity%20Files/Nutrition/DRIs/ULs%20for%20Vitamins%20and%20Elements.pdf, accessed 13 August 2013
  4. Biologische Krebsabwehr: Selen. http://www.biokrebs-heidelberg.de/images/stories/download/Therapie_Infos/Selen.pdf (last access 29/06/2013).
  5. Fakih MG, Pendyala L, Brady W, Smith PF, Ross ME, Creaven PJ, Badmaev V, Prey JD, Rustum YM. A Phase I and pharmacokinetic study of selenomethionine in combination with a fixed dose of irinotecan in solid tumors. Cancer Chemother Pharmacol 2008; 62(3): 499-508.
  6. Reilly C. Selenium in food and health. 2nd Edition. New York: Springer 2006.
  7. Rayman, MP: Selenium and human health. Lancet 2012; 379: 1256–68.
  8. National Cancer Institute: Antioxidants and Cancer Prevention: Fact Sheet http://www.cancer.gov/cancertopics/factsheet/prevention/antioxidants (last access 29/06/2013).
  9. Nagel G, Hoyer H, Katenkamp D. Use of complementary and alternative medicine by patients with breast cancer: observations from a health-care survey. Support Care Cancer 2004; 12(11): 789-96.
  10. Bruns F, Glatzel M, Schönekaes K, Riesenbeck D, Mücke R, Büntzel J, Micke P, Schäfer U, Kisters K, Micke O. Complementary and alternative medicine experience in radiation oncology patients: first results of a multi-center approach. Trace Elements & Electrolytes 2006; 23(4): 318-26.
  11. Sehouli J, David M, Kaufmann B, Lichtenegger W. Unkonventionelle Methoden in der Krebsmedizin - Postoperative Nutzung durch Patientinnen mit gynäkologischen Malignomen [Use of alternative treatments by patients after surgery for gynecologic malignancies]. Geburtsh Frauenheilk 2000; 60: 147-54.
  12. Bishop FL, Rea A, Lewith H, Chan YK, Saville J, Prescott P, von Elm E, Lewith GT: Complementary medicine use by men with prostate cancer: a systematic review of prevalence studies. Prostate Cancer and Prostatic Diseases 2011:14, 1–13.
  13. OTC ingredient tables. http://www.aesgp.be/facts-figures/otc-ingredients/ (accessed 29/06/2013).
  14. Asfour IA, Fayek M, Raouf S, Soliman M, Hegab HM, El-Desoky H, Saleh R, Moussa MA. The impact of high-dose sodium selenite therapy on Bcl-2 expression in adult non-Hodgkin's lymphoma patients: correlation with response and survival. Biol Trace Elem Res 2007; 120(1-3): 1-10.
  15. Karp DD, Lee SJ, Keller SM et al. Randomized, double-blind, placebo-controlled, phase III chemoprevention trial of selenium supplementation in patients with resected stage I non-small-cell lung cancer: ECOG 5597. J Clin Oncol 2013;31(33):4179-87.
  16. Dennert G, Horneber M. Selenium for alleviating the side effects of chemotherapy, radiotherapy and surgery in cancer patients. Cochrane Database of Systematic Reviews 2006, Issue 3. Art. No.: CD005037.
  17. Kasseroller R. Sodium selenite as prophylaxis against erysipelas in secondary lymphedema. Anticancer Res 1998; 18(3C): 2227-30.
  18. Zimmermann T, Leonhardt H, Kersting S, Albrecht S, Range U, Eckelt U. Reduction of postoperative lymphedema after oral tumor surgery with sodium selenite. Biol Trace Elem Res 2005; 106(3):193-203.
  19. Mücke R, Schomburg L, Glatzel M, Berndtskorka R, Baaske D, Reichl B, Büntzel J, Kundt G, Prott FJ, DeVries A, Stoll G, Kisters K, Bruns F, Schaeffer U, Willich N, Micke O, German Working Group Trace Elements and Electrolytes in Oncology - AKTE: Multicenter phase 3 trial comparing selenium supplementation with observaton in gynecologic radiation oncology. Int J Radiat Oncol Biol Phys 2010; 78: 828-835; doi:10.1016/j.ijrobp.2009.08.013.
  20. Buentzel J, Micke O, Glatzel M, Bruns F, Kisters K, Muecke R: Evaluation of the effect of selenium on radiation-induced toxicities in head neck cancer patients (abstract). J Clin Oncol 27, 2009 (suppl; abstr e20698); http://meetinglibrary.asco.org/content/33802-65 (last accessed 29/06/2013)
  21. Büntzel, J, Riesenbeck, D, Glatzel, M, Berndt-Skorka, R, Riedel, T, Mücke, R, Kisters, K, Schönekaes, KG, Schäfer, U, Bruns, F, Micke, O: Limited effect of selenium substitution in the prevention of radiation-associated toxicities. Results of a randomized study in head and neck cancer patients. Anticancer Res 2010; 30: 1829-1832.
  22. Büntzel, J, Micke, O, Kisters, K, Bruns, F, Glatzel, M, Schönekaes, K, Kundt, G, Schäfer, U, Mücke, R: Selenium substitution during radiotherapy of solid tumours – laboratory data from two observation studies in gynaecological and head and neck cancer patients. Anticancer Res 2010; 30: 1783-1786.
  23. Hu YJ, Chen Y, Zhang YQ, Zhou MZ, Song XM, Zhang BZ, Luo L, Xu PM, Zhao YN, Zhao YB, et al. The Protective Role of Selenium on the Toxicity of Cisplatin-Contained Chemotherapy Regimen in Cancer Patients. Biol Trace Elem Res 1997; 56: 331-41.
  24. Reid ME, Stratton MS, Lillico AJ, Fakih M, Natarajan R, Clark LC, Marshall JR: A report of high-dose selenium supplementation: response and toxicities. J Trace Elem Med Biol 2004; 18(1):69-74.
  25. Lippman SM, Klein EA, Goodman PJ, et al: Effect of Selenium and Vitamin E on Risk of Prostate Cancer and Other Cancers: The Selenium and Vitamin E Cancer Prevention Trial (SELECT). JAMA 2009; 301(1):39-51
  26. Sutter ME, Thomas JD, Brown J, Morgan B. Selenium toxicity: a case of selenosis caused by a nutritional supplement. Ann Intern Med 2008;148(12): 970-1.
  27. Stranges S, Marshall JR, Natarajan R, Donahue RP, Trevisan M, Combs GF, Cappuccio FP, Ceriello A, Reid ME: Effects of Long-Term Selenium Supplementation on the Incidence of Type 2 Diabetes: A Randomized Trial. Ann Intern Med 2007; 147:217-223.
  28. Pfeffer H. Schwerwiegender Zwischenfall bei Selen-Medikation. Hamburger Zahnärzteblatt 2002;42(3): 3.
  29. See KA, Lavercombe PS, Dillon J, Ginsberg R. Accidental death from acute selenium poisoning. Med J Aust 2006; 185(7): 388-9.
  30. SCF (Scientific Committee on Food): Opinion of the Scientific Committee on Food on the Tolerable Upper Intake Level of Selenium. 2000. http://ec.europa.eu/food/fs/sc/scf/out80g_en.pdf (accessed 01/10/2012).
  31. Duffield-Lillico AJ, Reid ME, Turnbull BW, Combs GF, Jr., Slate EH, Fischbach LA, Marshall JR, Clark LC. Baseline characteristics and the effect of selenium supplementation on cancer incidence in a randomized clinical trial: A summary report of the Nutritional Prevention of Cancer Trial. Cancer Epidemiol Biomarkers Prev 2002; 11(7): 630-9.
  32. Sandström B: Micronutrient interactions: effects on absorption and bioavailability. Br J Nutr 2001; 85: S181-S185.