The functions of selenium supplements

skin-cells antioxidant
Selenium is an important component of the antioxidant defense in the cells. It helps to protect against oxidative damage to both cells and DNA. It has been shown to have a protective effect against the damage to skin cells caused by ultraviolet radiation.

Why the interest in selenium facts?  Here, at the beginning of the website, we want to review in broad terms what we know about the functions of selenium supplementation. We are especially interested in selenium’s antioxidant and anti-inflammatory effects in the human body.

Selenium is an essential trace element in the human diet, and, in many regions of the world, it is an absolutely necessary nutritional supplement.  It has many and diverse functions in the human body.

One of the interesting things about selenium is that it does not perform its functions as an element or an ion.  Instead, it functions as a component of more complex compounds.  In particular, it is an essential component of the 21st amino acid, selenocysteine.

Selenocysteine is a vital component of some 25 different selenoproteins at work in human cells and tissues.  Selenoproteins are selenocysteine-containing proteins that perform a variety of biological functions in the body.  Restoration and maintenance of selenoprotein levels beneficial to good health is one of the primary reasons for taking a daily selenium supplement.

Overview of selenium’s functions in the body
Animal studies, observational studies, and human intervention studies have shown that selenium is critical to the prevention of the development of diseases:

  • various forms of cancer
  • various form of cardiovascular disease

Studies have shown that selenium plays an important role in the treatment of diseases:

  • thyroid disorders
  • infectious diseases (including the HIV virus)
  • detoxification and elimination of heavy metals
  • neuro-degenerative diseases caused by oxidative stress

Selenium supplementation seems to be especially important for individuals in the following groups:

  • Elderly
  • Smokers

Studies seem to show that selenium supplementation is safe for individuals in the following groups:

  • diabetics
  • pregnant women

Low selenium status is associated with the following conditions:

  • poor immune function
  • cognitive decline

Higher selenium status is associated with the following health benefits:

  • anti-viral effects
  • successful human reproduction.

Selenium is an essential component of important selenoproteins and selenium-dependent antioxidant enzymes:

  • the glutathione peroxidases
  • the thioredoxin reductases
  • the iodothyronine deiododinases
  • the selenoprotein P

Selenium and the antioxidant defense of cells and DNA
Specifically, selenium is an essential component of antioxidant enzymes that defend the body against the harmful effects of free radicals and other reactive oxygen species that cause oxidative damage to cells and DNA.

The free radical theory of degenerative disease and ageing posits that reactive species and free radicals cause oxidative damage to cells and to DNA when the free radicals are produced to excess in the body over long periods of time and are not neutralized by antioxidants such as Coenzyme Q10 and vitamins C and E and various selenium-dependent enzymes.  Three dietary changes have been proposed to reduce the oxidative damage caused by free radicals:

  • Limiting caloric intakes
  • Limiting the intake of polyunsaturated fats
  • Supplementing the diet with selenium and other antioxidants

Funding for more clinical trials of selenium needed
Selenium is a relatively rare trace element.  It is an element that is unevenly distributed in the earth’s soil and is, consequently, unevenly distributed in available foodstuffs around the world. Its use in nutritional supplements and medical preparations cannot be patented.  Consequently, pharmaceutical companies are not willing to invest research funds into clinical trials of the safety and efficacy of selenium formulations.

The existing knowledge base on selenium supplementation would benefit from funding for follow-up studies on the following topics:

  • Optimal daily intakes of dietary selenium (including selenium in nutritional supplements)
  • Optimal formulations of selenium supplements in terms of absorption and specific health benefits
  • Optimal dosages of selenium supplementation in terms of absorption and specific health benefit
  • Effect of selenium supplementation on concentrations and activities of specific selenoproteins and selenium-dependent antioxidant enzymes

Overview of selenium supplementation and disease prevention
In the coming weeks and months, we will want to write about the results of clinical trials of selenium supplementation in greater detail.  In this article, we highlight the results of some of the most interesting clinical trials conducted to date.

Selenium and cancer clinical trials
Linxian, China, study (1993) = Daily supplementation with 50 micrograms of selenium together with beta-carotene and vitamin E supplements significantly reduced cancer mortality rates.

Nutritional Prevention of Cancer (NPC) clinical study (1996) = supplementation with 200 micrograms of a selenium yeast preparation daily reduced the risk of colon, lung, and prostate cancer significantly.

SU.VI.MAX study (2003) = supplementation with 100 micrograms of selenium together with vitamin C, vitamin E, beta-carotene, and zinc supplements reduced cancer incidence and cancer deaths significantly.

Bonelli adenoma recurrence study (2013) = Daily supplementation with 200 micrograms of selenium together with zinc, vitamin A, vitamin C, and vitamin E supplements for 5 years significantly reduced the recurrence of colonic adenomas.

Selenium and cardiovascular disease studies
KiSel-10 study (2013) = Daily supplementation of elderly, healthy, live-at-home Swedish citizens with 200 micrograms of an organic selenium yeast preparation and 200 milligrams of Coenzyme Q10 significantly reduced the incidence of cardiovascular death and significantly improved cardiac function. The researchers pointed to a special inter-relationship between selenium and Coenzyme Q10 that has proven to be cardio-protective. Using the two antioxidant substances in combination seems to confer greater health benefits.

Selenium and further known health benefits
In future articles on this website, we will want to summarize the results of randomized controlled trials of selenium supplementation on cancer, heart disease, thyroid disorders, HIV virus, heavy metal intoxication, diabetes and pregnancy.



Alehagen, U., Johansson, P., Björnstedt, M., Rosén, A., & Dahlström, U. (2013). Cardiovascular mortality and N-terminal-proBNP reduced after combined selenium and coenzyme Q10 supplementation: a 5-year prospective randomized double-blind placebo-controlled trial among elderly Swedish citizens. International Journal of Cardiology, 167(5), 1860-1866.

Alehagen, U., & Aaseth, J. (2015). Selenium and coenzyme Q10 interrelationship in cardiovascular diseases–A clinician’s point of view. Journal of Trace Elements in Medicine and Biology, 31157-162.

Blot, W. J., Li, J. Y., Taylor, P. R., Guo, W., Dawsey, S., Wang, G. Q., & Li, B. (1993). Nutrition intervention trials in Linxian, China: supplementation with specific vitamin/mineral combinations, cancer incidence, and disease-specific mortality in the general population. Journal of The National Cancer Institute, 85(18), 1483- 1492.

Bonelli, L., Puntoni, M., Gatteschi, B., Massa, P., Missale, G., Munizzi, F., & Bruzzi, P. (2013). Antioxidant supplement and long-term reduction of recurrent adenomas of the large bowel. A double-blind randomized trial. Journal of Gastroenterology, 48(6), 698-705.

Clark, L. C., Combs, G. J., Turnbull, B. W., Slate, E. H., Chalker, D. K., Chow, J., & Taylor, J. R. (1996). Effects of selenium supplementation for cancer prevention in patients with carcinoma of the skin. A randomized controlled trial. Nutritional Prevention of Cancer Study Group. JAMA, 276(24), 1957-1963.

Hercberg, S., Galan, P., Preziosi, P., Bertrais, S., Mennen, L., Malvy, D., & Briançon, S. (2004). The SU.VI.MAX Study: a randomized, placebo-controlled trial of the health effects of antioxidant vitamins and minerals. Archives of Internal Medicine, 164(21), 2335-2342.

Klein, E. A., Thompson, I. J., Tangen, C. M., Crowley, J. J., Lucia, M. S., Goodman, P. J., & Baker, L. H. (2011). Vitamin E and the risk of prostate cancer: the Selenium and Vitamin E Cancer Prevention Trial (SELECT). JAMA, 306(14), 1549-1556.

Lippman, S. M., Klein, E. A., Goodman, P. J., Lucia, M. S., Thompson, I. M., Ford, L. G., & Coltman, C. J. (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, 301(1), 39-51.

McKenzie, R. C. (2000). Selenium, ultraviolet radiation and the skin. Clinical And Experimental Dermatology, 25(8), 631-636.

Rayman, M. P. (2012). Selenium and human health. Lancet (London, England), 379(9822), 1256-1268.

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