Purported Benefits, Side Effects & More


Purported Benefits, Side Effects & More

Common Names

  • Selenocysteine
  • Selenomethionine
  • Selenate
  • Selenite

For Patients & Caregivers

Tell your healthcare providers about any dietary supplements you’re taking, such as herbs, vitamins, minerals, and natural or home remedies. This will help them manage your care and keep you safe.

What is it?

There is no clear evidence to support the use of selenium for cancer prevention.

Selenium is an element obtained in the diet from seafood, poultry, meats, cereals, nuts, and grains. It is an essential part of cellular antioxidant systems that protects cells from DNA damage and mutations. For this reason, it has been studied for prevention of diseases caused or aggravated by this type of damage including cancer, heart disease, and diabetes. Selenium is also necessary for proper immune function, but it is not known whether higher-than-normal levels of selenium can stimulate the immune system.

Long-term use of selenium may increase the risk of certain types of cancer, and large doses can cause serious side effects.

What are the potential uses and benefits?
  • To prevent or treat cancer

    Clear evidence is lacking. Some studies suggest it may actually increase the risk of aggressive and secondary cancers.
  • To reduce cancer treatment side effects

    Preliminary studies suggest it may reduce some side effects caused by cancer treatments, but additional studies are needed.
  • To prevent heart disease

    Although low blood selenium levels have been associated with heart disease, studies do not support the use of selenium to protect against heart disease.
  • To prevent diabetes

    Supplementation is not useful in preventing diabetes and in some cases may increase the risk for this disease.
  • To stimulate the immune system

    A few studies suggest enhanced immune response, but more studies are needed.
What are the side effects?

With doses >1000 micrograms per day: Muscle weakness, fatigue, nerve pain, skin irritation, nail and hair changes/loss, garlic breath/body odor, irritability, and liver damage.

Accidental overdose: Gram quantities of selenium can cause severe GI and nerve problems, breathing distress, kidney or heart problems, and in one reported case led to death.

What else do I need to know?

Special Point:

  • Daily recommended intake: 55 micrograms, which is usually provided by seafood, meat, and fortified grain products.
  • Tolerable upper level of selenium: 400 micrograms per day. Higher dosages can cause toxicity.
  • Supplementation in patients with low levels or during active treatment should be under the guidance of healthcare practitioners.

For Healthcare Professionals

Clinical Summary

Selenium, an essential dietary trace mineral, is an important component of cellular antioxidant defense systems that include enzymes such as glutathione peroxidase (1). It also plays an important role in thyroid function. Selenium can be obtained from the diet by consuming whole grains, meats, seafood, poultry, and nuts. It is sold in supplemental form to boost immune function and for disease prevention.

Studies on the role of selenium in reducing cardiovascular disease risk are inconclusive (23) (28), although a meta-analysis suggests benefit with antioxidant mixtures when they contain selenium (48). Data are also mixed on whether supplementation can reduce viral load in patients with HIV (19) (49). Although it may improve glucose metabolism and reduce markers of inflammation and oxidative stress (41), supplementation is not useful in preventing diabetes and in some cases may increase the risk (20) (30) (42) (50). Selenium alone or in combination with vitamin E also did not prevent dementia (43).

In studies on the relationship between selenium and cancer prevention, data suggest it may help prevent gastrointestinal (16) (36) and lung (17) cancers, although findings from bladder cancer research are conflicting (26) (38) (44). Other studies on whether selenium status impacts cancer risk are also mixed (51) (52) (53), and a review of RCTs did not find clear evidence of cancer preventive potential (29).

In addition, the Selenium and Vitamin E Cancer Prevention Trial (SELECT) failed to find protective effects against prostate cancer (8) (21) or colorectal adenomas (45). In other studies, selenium along with soy and vitamin E did not prevent prostate cancer progression (27), and selenium taken with lycopene did not modulate prostate cancer risk (46). Moreover, selenium levels may influence the risk of aggressive prostate cancer (22), and supplementation may increase prostate cancer mortality (37).

A chemoprevention trial of selenium in patients with non-small cell lung cancer did not show benefit, but did suggest a possible nonsignificant increase in secondary lung cancers (25). Long-term supplementation may increase the risk for certain types of skin cancer as well (13).

With respect to dietary intake, no association between dietary selenium and thyroid cancer incidence was found (35).

A few studies suggest selenium supplementation may reduce some cancer treatment side effects including hair loss, abdominal pain, loss of appetite (15), diarrhea (24) (39), fatigue and nausea (40), head and neck lymphedema (12) (14), and salivary gland damage (47). However, more studies are needed and supplementation in patients with low levels or during active treatment should be under the guidance of healthcare practitioners in cancer populations.

Food Sources

Seafood, poultry, meat, whole grains, and nuts

Purported Uses and Benefits
  • Cancer
  • Cardiovascular disease
  • Diabetes
  • Immune function
Mechanism of Action

Selenium is an essential structural element of the antioxidant enzyme glutathione-peroxidase that converts aggressive oxidation products and intracellular free radicals into less reactive or neutral components (3). Other biological functions of selenium include regulation of thyroid hormone action and regulation of the reduction status of vitamin C (2).

In lab studies, selenium protected against adriamycin-induced cardiac dysfunction via restoring ATP-sensitive potassium channel expression (34). It induced a multitargeted cell death process characterized by unfolded protein response, ER-stress, and occurrence of large cytoplasmic vacuoles in addition to ROS formation (31). However, excessive selenium intake induces hepatic insulin resistance through an opposite regulation of ROS (32). The effects of dietary selenium on progression of malignant mesothelioma tumors depend on arising cancer cell redox metabolism and tumor ability to benefit from increased selenium intake (33).

Adverse Reactions

Case reports

Accidental overdose and death: Of a 75-year-old man from 10 g oral sodium selenite to self-treat prostate cancer after Internet reading on the subject (18). Consumption of gram quantities of selenium can cause severe GI and neurological disturbances, acute respiratory distress syndrome, myocardial infarction, and renal failure.

Chronic selenosis (doses >1000 mcg/day): Muscle weakness, fatigue, peripheral neuropathy, dermatitis, nail and hair changes/loss, garlic breath/body odor, irritability, growth retardation, hepatic necrosis.

Dosage (OneMSK Only)
  1. Whitney EN, et al. Understanding Normal & Clinical Nutrition, 4th ed. Belmont (CA): West Publishing; 1994.
  2. Dietary Reference Intakes for Vitamin C, Vitamin E, Selenium, and Carotenoids. Washington (DC): National Academy Press; 2000.
  3. Suadicani P, Hein HO, Gyntelberg F. Serum selenium concentration and risk of ischaemic heart disease in a prospective cohort study of 3000 males. Atherosclerosis 1992;96:33-42.
  4. Feifer AH, Fleshner NE, Klotz L. Analytical accuracy and reliability of commonly used nutritional supplements in prostate disease. J Urol 2002;168:150-4.
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  8. Klein EA, et al. SELECT: the selenium and vitamin E cancer prevention trial: rationale and design. Prostate Cancer Prostatic Dis 2000;3:145-51.
  9. Duffield-Lillico AJ, et al. 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 Biomarker Prev 2002;11:630-9.
  10. Clark LC, et al. Effects of selenium supplementation for cancer prevention in patients with carcinoma of the skin. A randomized controlled trial. JAMA 1996;276:1957-63.
  11. Klein EA, et al. SELECT: the selenium and vitamin E cancer prevention trial. Urol Oncol. 2003 Jan;21(1):59-65.
  12. Micke O, et al. Selenium in the treatment of radiation-associated secondary lymphedema. Int J Radiat Oncol Biol Phys . 2003 May 1;56(1):40-9.
  13. Duffield-Lillico AJ, et al. Selenium supplementation and secondary prevention of nonmelanoma skin cancer in a randomized trial. J Natl Cancer Inst. 2003 Oct 1;95(19):1477-81.
  14. Bruns F, et al. Selenium in the treatment of head and neck lymphedema. Med Princ Pract. 2004;13(4):185-90.
  15. Sieja K and Talerczyk M. Selenium as an element in the treatment of ovarian cancer in women receiving chemotherapy. Gynecol Oncol. 2004;93:320-327.
  16. Bjelakovic G, et al. Antioxidant supplements for prevention of gastrointestinal cancers: a systematic review and meta-analysis. Lancet 2004;364:1219-28.
  17. Zhuo H, Smith AH, and Steinmaus C. Selenium and lung cancer: A quantitative analysis of heterogeneity in the current epidemiological literature. Cancer Epidemiol Biomarkers Prev 2004;13(5):771-778.
  18. See KA, Lavercombe PS, Dillon J, Ginsberg R. Accidental death from acute selenium poisoning. MJA 2006; 185(7):388-389.
  19. Hurwitz BE, Klaus JR, LLabre MM, et al. Suppression of Human Immunodeficiency Virus Type I Viral Load With Selenium Supplementation. Arch Intern Med 2007: 167:148-154.
  20. Stranges S, Marshall JR, Natarajan R, et al. Effects of Long-Term Selenium Supplementation on the Incidence of Type 2 Diabetes: A Randomized Trial. Ann Intern Med. 2007.
  21. 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 Jan 7;301(1):39-51.
  22. Chan JM, Oh WK, Xie W, et al. Plasma Selenium, Manganese Superoxide Dismutase, and Intermediate- or High-Risk Prostate Cancer. J Clin Oncol. 2009 Aug 1;27(22):3577-83.
  23. Alehagen U, Aaseth J, Alexander J, Johansson P. Still reduced cardiovascular mortality 12 years after supplementation with selenium and coenzyme Q10 for four years: A validation of previous 10-year follow-up results of a prospective randomized double-blind placebo-controlled trial in elderly. PLoS One. 2018 Apr 11;13(4):e0193120.
  24. Muecke R, Schomburg L, Glatzel M, et al. Multicenter, Phase 3 Trial Comparing Selenium Supplementation With Observation in Gynecologic Radiation Oncology. Int J Radiat Oncol Biol Phys. 2010 Nov 1;78(3):828-35.
  25. Karp DD, Lee SJ, Shaw Right GL, et al. A phase III, intergroup, randomized, double-blind, chemoprevention trial of selenium (Se) supplementation in resected stage I non-small cell lung cancer (NSCLC). J Clin Oncol 28:7s, 2010 (suppl; abstr CRA7004).
  26. Amaral AF, Cantor KP, Silverman DT, and Malats N. Selenium and Bladder Cancer Risk: a Meta-analysis. Cancer Epidemiol Biomarkers Prev. 2010;19(9):2407-15.
  27. Fleshner NE, Kapusta L, Donnelly B, et al. Progression From High-Grade Prostatic Intraepithelial Neoplasia to Cancer: A Randomized Trial of Combination Vitamin-E, Soy, and Selenium. J Clin Oncol. Jun 10;29(17):2386-90.
  28. Jenkins DJA, Spence JD, Giovannucci EL, et al. Supplemental Vitamins and Minerals for CVD Prevention and Treatment. J Am Coll Cardiol. 2018 Jun 5;71(22):2570-2584.
  29. Vinceti M, Filippini T, Del Giovane C, et al. Selenium for preventing cancer. Cochrane Database Syst Rev. 2018 Jan 29;1:CD005195.
  30. Rayman MP. Selenium and human health. Lancet. 2012 Feb 29. doi:10.1016/S0140-6736(11)61452-9.
  31. Wallenberg M, Misra S, Wasik AM, et al. Selenium induces a multi-targeted cell death process in addition to ROS formation. J Cell Mol Med. 2014 Apr;18(4):671-84.
  32. Wang X, Zhang W, Chen H, et al. High selenium impairs hepatic insulin sensitivity through opposite regulation of ROS. Toxicol Lett. 2014 Jan 3;224(1):16-23.
  33. Rose AH, Bertino P, Hoffmann FW, et al. Increasing Dietary Selenium Elevates Reducing Capacity and ERK Activation Associated with Accelerated Progression of Select Mesothelioma Tumors. Am J Pathol. 2014 Apr;184(4):1041-1049.
  34. Liu ZW, Niu XL, Chen KL, et al. Selenium attenuates adriamycin-induced cardiac dysfunction via restoring expression of ATP-sensitive potassium channels in rats. Biol Trace Elem Res. 2013 Jun;153(1-3):220-8.
  35. O’Grady TJ, Kitahara CM, DiRienzo AG, et al. The association between selenium and other micronutrients and thyroid cancer incidence in the NIH-AARP Diet and Health Study. PLoS One. 2014 Oct 20;9(10):e110886.
  36. Hughes DJ, Fedirko V, Jenab M, et al. Selenium status is associated with colorectal cancer risk in the European prospective investigation of cancer and nutrition cohort. Int J Cancer. 2015 Mar 1;136(5):1149-61.
  37. Kenfield SA, Van Blarigan EL, DuPre N, et al. Selenium supplementation and prostate cancer mortality. J Natl Cancer Inst. 2014 Dec 12;107(1):360. 
  38. Beane Freeman LE, Karagas MR, Baris D, et al. Is the inverse association between selenium and bladder cancer due to confounding by smoking? Am J Epidemiol. 2015 Apr 1;181(7):488-95.
  39. Muecke R, Micke O, Schomburg L, et al. Multicenter, phase III trial comparing selenium supplementation with observation in gynecologic radiation oncology: follow-up analysis of the survival data 6 years after cessation of randomization. Integr Cancer Ther. 2014 Nov;13(6):463-7.
  40. Vieira ML, Fonseca FL, Costa LG, et al. Supplementation with selenium can influence nausea, fatigue, physical, renal, and liver function of children and adolescents with cancer. J Med Food. 2015 Jan;18(1):109-17.
  41. Bahmani F, Kia M, Soleimani A, Mohammadi AA, Asemi Z. The effects of selenium supplementation on biomarkers of inflammation and oxidative stress in patients with diabetic nephropathy: a randomised, double-blind, placebo-controlled trial. Br J Nutr. 2016 Oct;116(7):1222-1228.
  42. Tabrizi R, Akbari M, Moosazadeh M, et al. The Effects of Selenium Supplementation on Glucose Metabolism and Lipid Profiles Among Patients with Metabolic Diseases: A Systematic Review and Meta-Analysis of Randomized Controlled Trials. Horm Metab Res. 2017 Nov;49(11):826-830.
  43. Kryscio RJ, Abner EL, Caban-Holt A, et al. Association of Antioxidant Supplement Use and Dementia in the Prevention of Alzheimer’s Disease by Vitamin E and Selenium Trial (PREADViSE). JAMA Neurol. 2017 May 1;74(5):567-573.
  44. Goossens ME, Zeegers MP, van Poppel H, et al. Phase III randomised chemoprevention study with selenium on the recurrence of non-invasive urothelial carcinoma. The SELEnium and BLAdder cancer Trial. Eur J Cancer. 2016 Dec;69:9-18.
  45. Lance P, Alberts DS, Thompson PA, et al. Colorectal Adenomas in Participants of the SELECT Randomized Trial of Selenium and Vitamin E for Prostate Cancer Prevention. Cancer Prev Res (Phila). 2017 Jan;10(1):45-54.
  46. Morgia G, Voce S, Palmieri F, et al. Association between selenium and lycopene supplementation and incidence of prostate cancer: Results from the post-hoc analysis of the procomb trial. Phytomedicine. 2017 Oct 15;34:1-5.
  47. Son H, Lee SM, Yoon RG, et al.  Effect of selenium supplementation for protection of salivary glands from iodine-131 radiation damage in patients with differentiated thyroid cancer. Hell J Nucl Med. 2017 Jan-Apr;20(1):62-70.
  48. Jenkins DJA, Kitts D, Giovannucci EL, et al. Selenium, antioxidants, cardiovascular disease, and all-cause mortality: a systematic review and meta-analysis of randomized controlled trials. Am J Clin Nutr. Dec 10 2020;112(6):1642-1652.
  49. Muzembo BA, Ngatu NR, Januka K, et al. Selenium supplementation in HIV-infected individuals: A systematic review of randomized controlled trials. Clin Nutr ESPEN. Dec 2019;34:1-7.
  50. Kim J, Chung HS, Choi MK, et al. Association between Serum Selenium Level and the Presence of Diabetes Mellitus: A Meta-Analysis of Observational Studies. Diabetes Metab J. Aug 2019;43(4):447-460.
  51. Zhu X, Pan D, Wang N, et al. Relationship Between Selenium in Human Tissues and Breast Cancer: a Meta-analysis Based on Case-Control Studies. Biol Trace Elem Res. Dec 2021;199(12):4439-4446.
  52. Kho PF, Glubb DM, Thompson DJ, et al. Assessing the Role of Selenium in Endometrial Cancer Risk: A Mendelian Randomization Study. Front Oncol. 2019;9:182.
  53. Outzen M, Tjønneland A, Hughes DJ, et al. Toenail selenium, plasma selenoprotein P and risk of advanced prostate cancer: A nested case-control study. Int J Cancer. Feb 15 2021;148(4):876-883.
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