Selenium protects against cancer?

Selenium helps to protect against cancer, see Selenium Medicine by Dr. Mark Sircus:


Quote from the Pauling institute (2):

There is a great deal of evidence indicating that selenium supplementation at high levels reduces the incidence of cancer in animals. More than two-thirds of over 100 published studies in 20 different animal models of spontaneous, viral, and chemically induced cancers found that selenium supplementation significantly reduces tumor incidence. The evidence indicates that the  methylated forms of selenium are the active species against tumors, and these methylated selenium compounds are produced at the greatest amounts with excess selenium intakes. The relationships of selenium intake to cancer in humans and selenium status to tumor incidence in animals have been summarized.

Is it safe?

At this dosage, it is completely non-toxic.

The tolerable upper limit (2) is 400 micrograms (mcg) per day.

Quote from the Pauling institute on selenium toxicity (2):

Although selenium is required for health, like other nutrients, high doses of selenium can be toxic. Acute and fatal toxicities have occurred with accidental or suicidal ingestion of gram quantities of selenium. Clinically significant selenium toxicity was reported in 13 individuals after taking supplements that contained 27.3 milligrams (27,300 mcg) per tablet due to a manufacturing error.


200 micrograms (mcg) of selenium l-selenomethionine per day. This is the organic form of selenium, and at this level is completely safe (2).

You can also substitute Brazil Nuts. One brazil nut contains approximately 100 micrograms (mcg) of selenium, so two brazil nuts per day will provide your selenium needs [citation required].

Do not take any other forms of inorganic selenium. Selenium selenite is used to reliably induce cataracts in rats (1)



The balance of evidence for vs. balance of evidence against is positive, as shown by the referenced papers above.


Question: There is no evidence to show that selenium is effective against cancer?

This is the wrong question. If you hear somebody use these exact words, then they trying to dismiss selenium as a factor in preventing cancer.

The correct questions are:

  • “Is the balance of evidence in favour of taking selenium to prevent cancer?”, or;
  • “Is selenium more likely to help than harm?”

The answer to these two questions is yes, and yes, because all the evidence points towards selenium playing a role in cancer prevention.

At some point in the future, there will be a large scale, double blind medical study for selenium and cancer, and the probability that selenium is definitely effective will approach 100%. However, until then, we have to use Bayes theorem to work with the best evidence we have: the probability of help vs. harm is not quite 100%, but it is definitely well above 90%.



Leave a Reply

Your email address will not be published.