Antioxidants Encourage Cancer in Some Cases, Study Says

Anil Ananthaswamy
for National Geographic News
August 19, 2009
Antioxidants, often praised for their reported cancer-fighting power, could in fact be aiding the growth of cancer in some situations, a new study says.

It's well known that in lab tests antioxidants—found in many vegetables and whole grains—can prevent the formation of tumors by preventing free radicals, or highly reactive molecules, from causing DNA damage.

Now, researchers have shown that antioxidants may have the opposite effect in human breast cells.

In a new experiment antioxidants behaved like cancer-causing agents, protecting cells that should otherwise have died—which allowed them to multiply and become cancerous.

"The survival of these cells could be contributing to [tumor creation], rather than the opposite," said study leader Zachary Schafer of the University of Notre Dame in Indiana.

Detached but Alive

Schafer and a team at Harvard Medical School cultured breast-tissue cells using a simulated scaffolding that mimics how cells grow in the body.

(Explore a human-body interactive.)

The cells formed a spherical structure that became hollowed out as the cells in the center detached from the cells on the scaffolding and died.

However, when the team introduced a cancer gene into the mix, the detached cells did not die—just as happens in the body.

"This happens in early breast cancer lesions," said Schafer, whose work was reported today online in the journal Nature.

The researchers, meanwhile, noticed that the normal, detached cells without the cancer gene were being damaged by naturally occurring free radicals.

Also, the detached cells were not producing enough ATP, a critical energy molecule.

The researchers added high concentrations of antioxidants to the cell culture in an effort to suppress the harmful free radicals and boost ATP production.

They found that antioxidants have exactly the same effect as the cancer gene: The detached cells did not die.

This is because the antioxidants are helping the cells recover their ability to produce ATP, Schafer said. The cancer gene also restored ATP production in the cells.

Complex Antioxidant Debate

The findings agree with previous research.

A 2008 paper in the Journal of the National Cancer Institute, for example, recommended that people should not take supplemental antioxidants during chemotherapy and radiation therapy, as these supplements could protect tumors.

"This work highlights another aspect of the complexity of understanding the antioxidant debate in cancer development," said Brian Lawenda, the lead author on the 2008 paper, who was not involved in the new research.

Depending on the circumstances, an antioxidant compound can either have tumor-causing or tumor-killing effects, added Lawenda, clinical director of the radiation oncology division at the Naval Medical Center in San Diego, California.

Too Early to Tell

But it's too early to jump to conclusions that antioxidants are bad, study leader Schafer pointed out.

This was just a study on one cell line, and more work is needed, for example, using cells inside animals and testing different types of cells, he said.

Also, the high antioxidant concentration used in the study is unlikely to be achieved in the human body by simply eating antioxidant-rich foods or vitamins.

(Related: "Coffee Buzz: Drink Is Top Antioxidant Source in U.S.")

"We are not making any sort of suggestion that people should alter their diet. We simply cannot extrapolate these findings to dietary intake at this time," Schafer said.

The Naval Medical Center's Lawenda also cautioned that people should not overreact.

"It is important for the general public to understand that antioxidant compounds in whole foods likely are protective against cancer development," he said.

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