Antioxidants May Facilitate The Spread Of Cancer

Antioxidants May Make Cancer Worse, Scientific American, October 2015

Scientists now think that antioxidants, at high enough levels, also protect cancer cells from these same free radicals. “There now exists a sizable quantity of data suggesting that antioxidants can help cancer cells much like they help normal cells.”

The study that this article was based on was done on mice and used the antioxidant  N-acetylcysteine (NAC). The researchers also tested human melanoma cells with a form of vitamin E. In all of their tests, antioxidants caused cancer cells, melanoma cells in this case, to metastasize or spread.

When the body is given extra antioxidants, its tumor cells get to keep more of the antioxidants that they already make themselves. The [cancer] cells can store the surplus, improving their ability to survive damage.

It’s not so much that antioxidants caused cancer (initiation), but that they promoted the spread of existing, perhaps undiagnosed, cancer (progression).

In other words, it “could be that while antioxidants might prevent DNA damage — and thus impede tumor initiation — once a tumor is established, antioxidants might facilitate the malignant behavior of cancer cells.”

In some of their previous research this team found that antioxidants also protected lung cancer cells and breast cancer cells. There have been some epidemiological studies that support this well:

  • A large trial reported in 1994 that daily megadoses of the antioxidant beta-carotene increased the risk of lung cancer in male smokers by 18 percent.
  • A 1996 trial was stopped early after researchers discovered that high-dose beta-carotene and retinol, another form of vitamin A, increased lung cancer risk by 28 percent in smokers and workers exposed to asbestos.
  • A 2011 trial involving more than 35,500 men over 50 found that large doses of vitamin E increased the risk of prostate cancer by 17 percent.

Here’s the study it referenced:

Antioxidants Can Increase Melanoma Metastasis In Mice, Science Translational Medicine, October 2015

All of this work is about antioxidants from supplements, not from food. Not saying eating lots of antioxidants from food wouldn’t do the same thing, but it wasn’t addressed here.

Here’s a list of some antioxidants. Some of these, like vitamin E, selenium, and beta-carotene, have been linked to cancer, in supplement form.

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