Could antioxidants make cancer worse?

Could antioxidants make cancer worse? Photo: Thinkstock

When antioxidants pop up in health news, it's usually because they're being lauded as powerful cancer fighters.

And that makes sense: Antioxidants, found in abundance in red wine, dark chocolate, blueberries, and tons of other foods, fight free radicals, or highly reactive molecules that run amok in the body, breaking into cells, damaging DNA, and potentially leading to cancer. But new research published in Nature shows that antioxidants—yes, the same ones that we've been told to gobble down to prevent cancer—could actually make the disease worse.

Researchers from University of Texas Southwestern Medical Center took skin cancer cells from human patients and injected them into mice. Some of the mice were injected with high doses of a supplemental antioxidant, while others were not. They found that giving mice antioxidants made the melanoma spread to other parts of the body much faster than if they had been given no supplement at all.

What gives? When a tumour releases cancer cells into the bloodstream, antioxidants can help keep those cells alive, increasing their chances of forming a new tumour elsewhere in the body, says Sean Morrison, director of UT Southwestern's Children's Medical Center Research and lead author of the study. In fact, cancer cells seem to benefit from antioxidants even more than normal, healthy cells do.

This concept isn't new: Previous human trials testing the effects of antioxidants on lung cancer were stopped early because the patients who took concentrated doses of antioxidant supplements got more tumours than patients who didn't get the pills. This new study in mice offers an explanation for why antioxidants seem to make cancers spread.

So does this mean you should stop eating antioxidant-rich foods like blueberries and olive oil? Definitely not. First of all, this study was done in mice infected with human cancer cells, so the results cannot be applied to healthy humans who don't have cancer. Plus, Morrison explains, there's no reason to fear foods that naturally contain lots of antioxidants.

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"There's a difference between eating a healthy diet and taking pills with whopping doses of antioxidants," he says. "If you're getting antioxidants from food, it's a slow release into your body. If you take a pill that's packed with antioxidants like vitamin E and A, then you get this burst with very different effects than what you'd get from food. Some of these pills have hundreds or a thousand times the daily recommended requirement."

The bottom line: Follow the advice given by experts: If you have cancer, it's probably best to avoid antioxidant supplements.

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And if you don't have cancer, remember that research in this area is always changing and getting more complex, so it's probably not wise to make loading up on antioxidants your singular nutritional goal. It's also another reason to think twice about shelling out a lot of money for products that tout super-high antioxidant content, like acai berries or baobab powder: Scientists have already said that the antioxidant "score" you see on food packages has no relevance to human health—basically, it's just a meaningless marketing claim.

In short, it's something you've heard many times before: "Eat a healthy diet with all things moderation," Morrison says.

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