Selenium is a very important trace mineral in human nutrition. It displays powerful ‘cleaning up” or anti-oxidant abilities which neutralize toxic substances in the body. People living in western societies such as the U.S., often don’t get enough selenium in their diet and may even be grossly deficient.

There are numerous health benefits from ensuring a healthy intake of selenium including its anti-cancer properties. Large numbers of clinical studies have observed selenium’s ability to reduce the risk of many types of cancer.  Researchers have also found that selenium can influence gene expression to suppress tumour onset, growth and spread (metastasis).

In December 1996, an article was published in the Journal of the American Medical Association, documenting a study conducted by Dr Larry C. Clarke, of the University of Arizona Medical School, involving a group of 1312 people.  They were given 200 micrograms of selenium daily for ten years.  It was observed that selenium alone reduced the overall cancer mortality by a huge 50%. Prostate cancer was reduced by 63%, colorectal cancers by 58% and lung cancer by 46%, regardless of whether they were smokers or not. In another study conducted by the University of California, San Diego, selenium was seen to reduce breast cancer in women by 65-95% depending on the type.

Selenium deficiency increases your risk of cancer

Many large scale epidemiologic studies have shown that populations with low selenium levels have a significantly increased risk of developing different types of cancer. These studies show that having an adequate amount of dietary selenium can have preventive effects on common cancers.

Multiple studies show that low selenium levels in the blood, hair, or nail clippings are associated with a 2 – 3-fold increase in overall cancer risk. For some types of cancer such as thyroid cancer, the risk rises to nearly 8-fold. Selenium deficiencies are now known to increase the risk of cancers of the lung, bladder, stomach, esophagus, and liver.

Three forms of selenium most active in cancer prevention

Selenium can be obtained from a variety of different foods both from plant and animal sources. It comes in several forms and the body handles these in unique ways. The three forms of selenium most active in preventing cancer are –

  1. Sodium selenite
  2. L-selenomethionine
  3. Selenium-methyl L-selenocysteine

What are the important differences?

  • L-selenomethionine increases cancer cell death by apoptosis (cancer cell suicide), but only in cells with an intact "suicide" gene called p53.34.
  • Selenium-methyl L-selenocysteine induces apoptosis in mutated cancer cells that lack this suicide gene.
  • Inorganic sodium selenite more effectively increases genetic expression of a cell protector glutathione.

All three selenium compounds stimulate cell death in various types of cancer, but each compound is better at destroying some cancers than others.

Because of these synergies between the different forms of selenium, you can understand why all three forms of selenium taken together are much more effective at killing off early or developing cancers in your body.

Selenium-Methyl L-Selenocysteine

This is an organic combination of selenium with a sulfur-containing amino acid called L-cysteine. It is the most potent form of selenium known in nature, and selenium-methyl L-selenocysteine is found in plants of the allium family, e.g. garlic and onions, which are grown in selenium-enriched soils.

Selenium-methyl L-selenocysteine has the effect of inhibiting the formation of new blood vessels in tumours. This effect will reduce tumour growth.

Sodium Selenite

Sodium selenite destroys cancer cells by selectively generating toxic free radicals (reactive oxygen species) which target the destruction of the mitochondria in cancer cells, however not in healthy cells.

Sodium selenite helps with the repair of damaged genes (DNA segments). This reduces the risk of new cancers being formed.

Numerous human studies with sodium selenite support the use of this form of selenium as a possible additional treatment for cancer patients and for preventing new or recurring cases of cancer.

In a randomized controlled clinical trial of sodium selenite using 200 mcg per day versus a placebo in patients with aggressive head and neck cancers, patients given the supplement showed an increased ability to destroy cancer cells. In another study it was shown that temporary use of 1,000 mcg of sodium selenite in patients with oral tumors effectively reduced potentially deadly swelling in these patients after surgery. Sodium selenite in patients with newly diagnosed non-Hodgkin's lymphoma increased the response rate to chemotherapy by 50% compared to a placebo group, and significantly increased overall survival time.


An organic form of selenium combined with the sulfur bearing amino acid called L-methionine. It is the form of selenium found in most preparations of selenium-enriched yeast, which has been used in many clinical trials.

Laboratory tests demonstrate that L-selenomethionine inhibits growth of cancer cells at rates more than one thousand times greater than it does healthy normal tissue.

200 mcg of L-selenomethionine daily was given to patients with pre-cancerous tissue in their esophagus. This slowed the progression of potential cancerous cells and triggered regression of pre-cancerous cells to normal. This anti-cancer effect was stronger in patients with earlier changes than in those with more advanced cell abnormalities.

Dr. Larry C. Clark of the University of Arizona conducted a trial to prevent skin cancers in 1996 with a daily dose of 200 mcg of L-selenomethionine. Unfortunately it was revealed to be ineffective at preventing either of the two major skin cancers, however these patients were found to reap other anti-cancer benefits and they were significantly protected from death by all cancers (a 50% reduction compared with controls) and from developing any cancer (a 37% reduction).

In Conclusion

There is a large amount of scientific evidence now available to suggest that selenium has anti-cancer effects. A diet rich in selenium is beneficial, of course, however supplementation of all three types of selenium, L-selenomethionine, sodium selenite and selenium-methyl l-selenocysteine would be worthwhile to ensure you get all of the anti-cancer benefits.

Further links:

All three types of selenium are needed to maximize cancer protection and survival rates. WE know of at least twelve mechanisms by which these selenium compounds do this. Future research will reveal more.

  1. Regulation of lipoxygenase enzymes which produce inflammatory molecules that stimulate cancer growth.
  2. Reduction of oxidative stress that causes free radical damage.
  3. Protection of selenoproteins, which recycle antioxidants.
  4. Detoxification of the body from cancer causing heavy metals.
  5. Induction of protective “phase 2” liver enzymes that neutralize many carcinogenic toxins.
  6. Inhibition of DNA alterations (genetic damage), which initiates cancerous changes in cells.
  7. Inactivation of molecular transcription factors required by cancer cells to support their growth and development.
  8. Shutting down of the essential cell replication cycle needed by cancer cells to produce their explosive growth.
  9. Induction of apoptosis, the programmed cell death, which is missing in cancer cells, allowing them to continue to reproduce indefinitely and potentially live forever.
  10. Enhanced immune system activity to detect and destroy incipient cancer cells.
  11. Down-regulation of sex hormone receptors used by certain cancers to sustain their growth.
  12. Limiting effects on tumor invasion and metastasis.

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