The limitations of antioxidants
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The limitations of antioxidants

Plenty of research shows that antioxidants such as vitamins A, C, and E can protect against heart disease, Alzheimer's, and even cancer. This is why companies plaster "high in antioxidants" claims on thousands of food, beverage, and supplement labels. But more is not necessarily better when it comes to antioxidants. Getting too many antioxidants can actually be dangerous.

A new study from Sweden found that high-dose vitamin E supplements sped up tumor growth in mice with lung cancer. According to lead researcher Martin Bergö, just as vitamin E safeguards healthy cells from disease (causing free radicals), it also fights free radicals in cancer cells. As a result, cancerous tumors are able to grow bigger and faster.

But does this mean antioxidant supplements are bad news for humans? Bergö thinks so. "Critics will say our research was just a mouse study, but I don't think we should even do these types of tests on humans," he says. "They've already killed enough people with antioxidants in human trials."

But other experts think Bergö is jumping the gun. "We can't just throw out 30 years of research showing their benefits based on mouse studies," says Eric Rimm, a professor of epidemiology and nutrition at Harvard School of Public Health.

Even if this study doesn't discount antioxidants, it does underscore the idea that more isn't always better. "What we'll probably discover is that there's a U-shaped curve with vitamin E and other antioxidants," says says Duffy MacKay, vice president of scientific and regulatory affairs at the Council for Responsible Nutrition. "When you don't get enough, the body suffers. Then there's a sweet spot where you get just enough and everything in the body works great. And then there's probably an upper limit for any benefits."

The best way to get the right amount and mix of antioxidants is through food. "We've survived as a species by being able to use the foods around us as efficiently as possible," says Rimm. "We're learning more and more that high-antioxidant foods such as blueberries, strawberries, and apples have other positive biological effects. You lose those when you isolate compounds and put them into a pill." Even so, he says, a good multivitamin with the full gamut of antioxidants can offer extra nutritional support for days when we don't eat as healthfully as we should.