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

Selenium – during cancer treatment

What is it?


The trace element selenium (Se) is nutritionally essential for human health and is naturally present in various food groups including grains, pulses, meat and fish. Although a number of health problems have been linked to selenium deficiency, selenium is also toxic in large doses. Selenium occurs naturally in a number of inorganic forms (e.g. selenite, selenate, selenide) and is also found in organic compounds (e.g. selenomethionine, selenocysteine). 1

For details on selenium in human nutrition, please refer to the summary: ‘Selenium – prevention’.


The element selenium was discovered in 1817 by the Swedish chemist Jöns Jakob Berzelius. In the 1930s, toxic properties of selenium were discovered in cattle, and in 1957, selenium was identified as an essential nutrient for mammals.


Licensed preparations for the treatment of selenium deficiency contain sodium selenite and can be obtained as liquid solutions for oral intake or intravenous administration. In addition, a large number of selenium-containing nutritional supplements or dietary aids are marketed for medical or health purposes. These contain either selenium alone (in inorganic or organic forms) or selenium in combination with other trace minerals as well as vitamins. Fermentation of yeast in a medium that is rich in inorganic selenium yields selenised yeast which contains 80–90% organic forms such as selenomethione, Se-methylselenocysteine and γ-glutamyl-Se-methylselenocysteine. 2

Application and dosage

Selenium supplements are marketed as tablets, capsules, pellets and liquid solutions for oral intake. Mono-selenium preparations usually contain 50–300µg selenium per single dose, while multi-component supplements usually contain between 30–50µg selenium.
Licensed preparations for the treatment of selenium deficiency contain sodium selenite and are available as liquid solutions for oral intake or intravenous administration.

Supplemental selenium is often taken in doses ranging from 50–200µg/day. The recommended daily allowance for adults is 55µg/day, which is sufficient to raise plasma selenium to 1–1.2µM and to maximise glutathione peroxidase; the upper limit is 400µg/day. 3 For the prevention and treatment of adverse effects of chemo- or radiotherapy, even higher doses have been recommended. 4

Fakih (2008) investigated whether selenium supplementation allowed the escalation of the dose of irinotecan above the maximum tolerated dose (125 mg/qm in weekly application). 5 The primary dose-limiting adverse effect of irinotecan is diarrhoea. This phase-1-dose escalation trial found that selenomethionine (2.200 µg/day) did not allow a safe dose-escalation of irinotecan; 3 of 4 evaluable participants who received the escalated dose suffered from dose-limiting diarrhoea.

Claims of efficacy/Alleged indication(s)

Selenium supplementation in people with cancer has been promoted for several distinct purposes:

  • Increasing the efficacy of conventional radio- and chemotherapy during cancer treatment.
  • Prevention of relapse or metastases in people with a complete remission of cancer.
  • Prevention and treatment of the adverse effects of conventional cancer therapy.

Mechanism(s) of action

Selenium is bound to selenoproteins in the human body after intestinal absorption and incorporated into proteins either specifically, in catalytically active selenoenzymes, or unspecifically in tissue proteins. 6

More than 25 selenium-containing enzymes have been identified to date. There are at least two functional groups of selenoproteins. The first is involved in redox processes in the tissue (glutathione peroxidases, thioredoxin reductase), the second in thyroid hormone metabolism (iodothyronine deiodinases). Furthermore, several selenoproteins have been linked to a variety of health conditions. 7

Selenium is claimed to be an antioxidant. An antioxidant is an agent that is able to lower the level of unstable and reactive molecules (free radicals, or reactive oxygen species; ROS) in the tissues, and in turn protect tissues against ROS-induced damage, which putatively contributes to cancer development and induces or aggravates the adverse effects of cancer therapy. 8

The bioavailability of ingested organic and inorganic selenium – as a function of absorption, metabolism and excretion – is reported to be between 50% and 90%, depending on the form of selenium and type of preparation. 6

Prevalence of use

Representative figures for the use of selenium supplements among people living with cancer are unavailable. Surveys from Germany suggest that between 4% and 10% of people with cancer use selenium supplements. 9-11 A systematic review of international studies on the use of complementary and alternative medicine in prostate cancer patients identified 11 studies, which reported 4–27% used selenium supplements. 12

Legal issues

Most, but not all, forms of selenium are freely marketable for human use within the EU (selenised yeast, for example, is not), but may be available to customers through Internet resellers. Licensed drugs for the treatment of selenium deficiency are available over the counter in most EU and other European countries; a prescription is required in Denmark and Germany (although in Germany only for preparations containing more than 50µg selenium). 13

Cost(s) and expenditures

The cost of 100 µg of inorganic selenium is around €0.50 (€0.15–1.60) via Internet pharmacies; this amounts approximately €15 a month.

Expenditures are higher for prescription drugs than for over-the-counter nutritional supplements, but may be reimbursable in some countries when the patient has a diagnosis of selenium deficiency.

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.


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