Can Selenium Protect You from Cancer?

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September 27, 2007 | 76,375 views

Dr. Donald W. Miller, a cardiac surgeon and Professor of Surgery at the University of Washington in Seattle, shares impressive research findings on the cancer-fighting properties of selenium.

As scientists have now determined, cells of all organisms, whether bacterial, animal, or non-animal, need selenium for proper functioning.

Selenium deficiency has been linked to a wide variety of disorders and diseases, including:

The Recommended Dietary Allowance (RDA), as set by the U.S. Food and Nutrition Board, is 55 mcg of selenium per day, based on two studies that show this amount of selenium supports the optimal generation of glutathione peroxidase. This is believed to be adequate for 98 percent of the population. 

However, this government recommendation did not take into account a previous finding that shows a dose four times higher (200 mcg) to have an anti-cancer effect, without being toxic. 

Some of the scientific explanations for selenium’s anti-cancer effect include: 

The first indications of selenium toxicity are "garlic breath" and dry skin. As the toxicity increases, your fingernails develop white patches, become brittle, and fall off. Hair and nail loss occurs once selenium intake reaches 4,990 mcg per day, according to one study. August 27, 2007


Indeed, making sure you get enough selenium appears to be a good idea for many. Especially if you live in an area with selenium-poor soils, as these areas tend to show higher cancer rates among their population than those living in selenium-rich soil areas.

I recently met Dr. William LaValley in Austin, Texas and was very impressed with his comprehensive perspective with therapeutic nutrition to treat disease states with natural therapies. He has spent many years carefully reviewing the literature and understanding these complex molecular biological pathways, to come up with something that makes sense clinically.

I asked him for his perspective and thought you might find it useful:

For prevention of cancer and other diseases associated with high oxidative causes, a little is good, up to  200 mcg per day, especially in the selenomethionine form.  Higher doses are possibly problematic.

In cancer treatment, however, there is a good evidence base to support the use of significantly higher doses in the correct dosage form -- especially the selenium selenite in liquid drops -- as part of a well-designed integrative and complementary medicine cancer treatment protocol.

This information may be misleading, however. 

The lower doses are recommended for prevention of the disease, while higher doses are used for treatment only after the cancer is diagnosed. The higher doses are for regulation of cell proliferation, via inducing apoptosis (programmed cell death).

Some natural health writers lead people to believe that 200 mcg of selenium will have cancer-fighting benefits through this pro-apoptotic mechanism.  I don't see the evidence supporting this. The 200 mcg lower dose of selenium is targeting the cellular antioxidant machinery that reduces the ROS burden -- therefore it is more likely to be anti-cancer, and since it also supports better cellular function -- it is  more likely to support your immune system. There are specific immune benefits in other molecular pathways as well.

The higher doses provoke reactive oxygen species (ROS) production and are cytotoxic in acute dosing.  Chronic, slow increases in doses of selenium probably allows your cells to adapt to the selenium without toxicity, except cells are then less able to respond to provide antioxidant benefits via GSSH.  (Cancer Res. 2001 Oct 1;61(19):7071.)

Bottom Line on Selenium

A little of high quality selenium is necessary for good health.  Acute higher doses are acutely cytotoxic and can be harmful or beneficial, depending on the intended use.  The evidence base supports the use of high doses under appropriate medical supervision for anti-cancer, proapoptotic stimulation and activation of molecular metabolic pathways that inhibit/block neoplastic proliferation.

For health maintenance, you should use selenium in a good bioavailable form, in a low dose (such as 200mcg).  This probably provides good anti-cancer benefits due to enhancing cellular pathways GSSH-GSH metabolism. You should avoid higher doses unless under supervision by a competent healthcare professional who understands the pathway stimulations being induced, and the should be reserved for targeting cancer that is already diagnosed. 

Do not use higher dose selenium for long term as an anti-cancer preventative.  High dose selenium is an inducer of ROS (superoxide anion) and can cause problems. 

The issue with antioxidant use and cancer prevention is tricky.  If someone has pre-cancerous stage cells or nascent cancer as yet undiscovered, then anti-oxidant use may well confer survival advantage to the cancer cells and make the situation worse.  These people need targeted pro-apoptotic, anti-cancer treatment.  The problem is, many of them don't (yet) know it.  The lung cancer studies that show that beta-carotene and Vitamin A use by smokers is associated with a bit greater cancer incidence is most likely due to this "undescribed" effect.

My thought prior to the release of these studies was that the use of certain antioxidants in smokers, if the sample size of the study were large enough, it would show that lung cancer incidence increased due to this (not yet widely understood antioxidant-conferring-survival-to-cancer-cells effect).  When the results came out, my thought was, 'of course, it's to be expected.'

The medical community was surprised and the natural health community went apoplectic.  I think very few understand the molecular biology and so the issue of personal bias plays into the response to the data.  I predict the same type of results for other cancers if the cohort size is adequate."

I appreciate Dr. LaValley’s willingness to share his expert thoughts on selenium.

Interestingly, "Chest" just published evidence-based clinical guidelines this month, including some for CAM therapies, and against some dietary supplements.  Please see Chest Sep 2007: 1S–19. If you would like more details on this fascinating subject I would encourage you to read this free full text journal article.