Do antioxidants cause cancer?

August 10, 2010
Volume 07    |   Issue 32

In November 2008, I wrote an article in Women’s Health Letter about the dangers of taking too many antioxidants. It explains that the way nutrients function is more important than their quantity. And that a high intake of antioxidants can actually backfire and have a pro-oxidant effect. This article also explains a test you can get to see how well your body uses the antioxidants in your supplements and foods. (You can read this article on my website.)

Now there’s more bad news about the dangers of taking high amounts of antioxidant supplements. According to a recent study, they can increase your risk for cancer.

This was an accidental discovery. The researchers were studying stem cells. They were looking for a way to reduce the genetic abnormalities that occur naturally when human heart stem cells multiply. This was when they stumbled upon an unexpected finding.

Frequently, researchers grow stem cells in a Petri dish culture that’s 20% oxygen. Cells grown in human tissues, however, are 3-5% oxygen. In this particular experiment, the research team discovered that there was a 9% rejection in laboratory grown stem cells because of genetic abnormalities. They decided to see whether there could be fewer abnormalities in these stem cells if they gave them high doses of antioxidants.

That’s when they made the discovery of a danger zone for the cells exposed to antioxidants. Once in this danger zone, the cells begin to develop genetic abnormalities. And these abnormalities predispose the cells to cancer.

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What does this mean for you and me?

Certainly, the way cells behave in an artificial environment like a laboratory Petri dish is not necessarily the same as how they react in our bodies. And all studies, when you examine them closely, have limitations. In this case, which antioxidants did they give? In what form and amount? Did they give them in balance with other nutrients? Etc.

What this study does is raise a question that I’ve raised before. Is it safe to take large amounts of antioxidants? Until we have more clarity, I suggest you look more at the balance of nutrients you take. Also, look at your body’s ability to absorb and utilize them. All of these are more important than the quantity. More may not be better at all. In fact, it could be much worse.

There is one caveat to this advice: We do know that in certain acute situations that high-doses of antioxidants can do wonders. For instance, taking 100,000 IU of vitamin A, which has antioxidant properties, during a severe cold or flu can stop the virus in its tracks. But you don’t want to take that dose for an extended period of time. It can be toxic. So avoid super high doses of any antioxidant, unless your doctor tells you to use them for a limited time for a specific purpose.

We also know that conventional doctors have a different view of what constitutes “high” doses than most integrative docs. For instance, many doctors think 5,000 IU of vitamin D is excessively high. But we know that spending time in the sun can produce 10,000 IU. So 5,000 IU really isn’t a “high” dose.

Your voice of reason in Women's Health,


Cedars-Sinai Medical Center (2010, May 4). High doses of antioxidant supplements induce stem cell genetic abnormalities, study finds. ScienceDaily. Retrieved May 5, 2010, from

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