Selenium in cancer

Selenium: a safe cytostatic agent for cancer

Due to its dual pro- and antioxidant effects, selenium is a "paradox" in cancer. It is successfully used at the ImunoMedica Clinic as a cytostatic for its antitumor and anti-metastatic action, as well as in a minimally invasive oncological approach, both to prevent cancer and support immunity.

Selenium is an essential micronutrient for immunity. It protects immune cells from oxidative stress through the redox regulating activity of selenoproteins. As a result, it is successfully used to treat a wide range of chronic diseases caused by oxidative stress, including cardiovascular disease, autoimmune diseases, neurological and mental illnesses, muscle disorders, and others.

It is also a powerful antiviral that plays an important role in anti-aging and boosts immunity. However, of all the health benefits, its role in cancer prevention and treatment receives the most attention.

Effects of selenium in cancer

  • Due to its potent immune stimulatory properties, selenium regulates immunity.
  • Selenium reverses immunosuppression in the tumor microenvironment by acting as an antioxidant, anti-inflammatory, and antiviral.
  • It has a dual role in cancer: chemopreventive antioxidant in nutritional doses and pro-oxidant in supranutritional doses.

In fact, in early 2009, the Food and Drug Administration (FDA) stated that "selenium may reduce the risk of certain cancers" and that "scientific evidence suggests that selenium consumption may reduce this risk". It is now known that selenium, vitamin E, and glutathione peroxidase work together to shield the body from the damaging effects of free radicals. According to studies, vitamin E and selenium have the ability to enhance one another's antiviral and antibacterial effects.

Selenium is a powerful antioxidant

Selenium functions as a double-edged sword in cancer, acting both as an antioxidant through selenoproteins at nutritional levels and as a pro-oxidant at supranutritional levels. At low nutritional doses, Selenium can act as an antioxidant, protecting cells from oxidative stress and promoting cell survival and growth. As a result, it serves as a chemopreventive agent.

In high doses, selenium is pro-oxidant

In higher, supernutritional pharmacological doses, selenium functions as a pro-oxidant, causing redox signalling and cell death in cancer tumors.

To date, many studies have been conducted on the benefits of selenium consumption in reducing the risk of cancer incidence at the nutritional level. These findings suggest that selenium acts as an immunostimulator, reversing immunosuppression in the tumor microenvironment and promoting antitumor immunity by activating the immune cells (e.g., M1 macrophages and CD8+ T lymphocytes) and releasing pro-inflammatory cytokines such as interferon gamma. There have been fewer studies on the effects of supranutritional or pharmacological selenium doses on cancer immunity.

What are the effects of selenium on cancer?

Chemopreventive Antioxidant

Selenium, in nutritional doses sufficient to saturate selenoproteins, acts as an antioxidant and chemopreventive agent by scavenging reactive oxygen species. It lowers the risk and prevalence of cancer by preventing DNA damage and mutations.

Pro-oxidant Cytostatic

Selenium induces oxidative stress in high, supranutritional or pharmacological doses. As a result, selenium also plays a pro-oxidant role in the fight against cancer. Because selenium boosts the activity of the antioxidant enzyme glutathione peroxidase in healthy tissues, it serves a dual purpose in fighting cancer and defending healthy cells. Selenium can produce oxygen radical molecules that can destroy cancer cell-specific mitochondria. Because of this, selenium has great potential for use as a cytostatic against cancer.

Reverses immunosuppression

Selenium regulates redox homeostasis and inflammatory pathways in cells, influencing the interaction between tumor cells and immune cells in the tumor microenvironment. Selenium supplementation acts on both innate immune cells (including neutrophils, macrophages, and NK cells) and adaptive immune cells, particularly T lymphocytes in the tumor microenvironment, reversing the immunosuppressive process.

Antimetastatic agent

It stops the migration, invasion and angiogenesis of cancer cells.

Antitumoral agent

Selenium has potent antitumor effects that are characterized by selective cytotoxicity on malignant cells that are resistant to conventional drug treatments. Furthermore, no damage to healthy or benign cells has been seen in these instances. This selective cytotoxicity is explained by the increased affinity for selenium of the proteins that confer drug resistance to cells.

Selenium's cytostatic effects have been shown to be most effective against the following cancers:

High-dose selenium treatment


The recommended dose of selenium is, on average, 200 μg per day. Randomised clinical trials have shown that the normal dose can go up to 400 μg per day. According to clinical experience, increasing this dose, up to 200 μg or 400 μg, depending on the patient, can have positive effects. Studies have shown a 50% reduction in the risk of prostate, lung, and colon cancer.

High-dose selenium treatment is a form of chemotherapy that has the advantage of being free from side effects, as healthy cells in the body are not affected. There are cases in the literature of cancer patients receiving more than 1000 μg of selenium intramuscularly, every other day for three weeks. By avoiding contact with the digestive juices, this method of administration ensures better assimilation.

Throughout treatment, the whole blood formula and liver function must be monitored.

In the ImunoMedica clinic, selenium is administered intravenously in doses of 2 mg with the goal of enhancing the cytostatic effects of selenium as well as providing protection against the adverse effects of chemotherapy, as demonstrated in studies that have been published thus far.

Adverse effects

  • The most common side effects of selenium poisoning are: garlic-scented halitosis, hair and nail loss, dermatitis, liver failure, and neuropathies.
  • There have been reports of cases where the organic form of selenium (selenomethionine) was administered at a dose of 7200 g twice daily for 7 days and no adverse effects were observed. The high tolerance and low toxicity of organic selenium allows a plasma concentration of 15 μM to be achieved, which increases the efficacy and decreases the toxicity of cytostatic treatment in animal models.
  • Excessive dosing may result in insulin resistance via hepatic damage caused by abnormal regulation of reactive oxygen species production. Consumption of omega-3 fatty acids during selenium treatment may reduce the amount of selenium absorbed by the body.
  • Taking selenium with certain herbs, such as angelica (Angelica archangelica), cloves (Caryophyllus aromaticus), garlic (Allium sativum), ginger (Zingiber officinalis), ginkgo (Ginkgo biloba), ginseng (Panax ginseng), may decrease blood clotting, increasing the risk of bleeding in some patients.
  • Selenium in high doses reduces vitamin C absorption.
  • Zinc can inhibit selenium absorption in the body. Selenium may increase the risk of bleeding during and after surgery. Selenium treatment should be discontinued at least two weeks before any surgery.