Are antioxidants always good for you? Actually, maybe not

Antioxidants are touted as the ultimate disease fighters—but that might not always be the case.

Why should you try this cleanse? Antioxidants. Why is this supplement superior? Well, it contains antioxidants, of course.

But what exactly are antioxidants and how do they impact your body? We delved into the science, and the answers to those questions may surprise you.


Antioxidants are a class of molecule that includes nutrients like vitamin A (also known as beta carotene), vitamin E, polyphenols (which have been linked to the benefits surrounding red wine), and other chemical compounds. Antioxidants are found in nature — in animals, fruits, and vegetables — but they can also be synthetically manufactured.

In your body, “antioxidants help to neutralize the negative action of excess free radical formation,” says Robert T. Mankowski, Ph.D., a research assistant professor and exercise physiologist at the University of Florida.

Any discussion of free radicals and their effects gets complicated quickly, but essentially, they have the potential to be harmful. The cells that make up your muscles, organs, and most other parts of your body are constantly working to keep you alive and healthy. To do that, your cells breathe, break down, reproduce, and perform a number of other functions — many of which require a chemical process called oxidation.

Oxidation produces free radicals, which in some cases can actually cause damage to your cells, research shows, causing a condition known as oxidative stress. This can trigger serious health issues, like cancer, heart disease, and Alzheimer’s.

Here’s where antioxidants come in. When you have too many of those free radicals floating around causing trouble, certain antioxidants — there are thousands of different types of them — can tie them up and keep them from doing harm, Mankowski says.


In some cases, they can even boost your health. One 2011 studysuggests the antioxidants in pecans may boost your heart health by lowering unhealthy LDL cholesterol. Research surrounding green teafinds its concentration of antioxidants may benefit your immune system, brain health, and cancer risk. What’s more, one study recently found that mushrooms are unusually high in antioxidants that may help your body fight aging. All good things, right? The list goes on and on.

If you have an excess supply of a single type of antioxidants — say, from a super-restrictive and quirky diet, or from a megadose antioxidant supplement — they can actually turn into pro-oxidants, meaning they promote the exact kind of damage antioxidants typically prevent, research shows.

That’s because free radicals aren’t always bad for you. In fact, they support some healthy and important changes within your body, says Mankowski. For instance, to help your muscles grow bigger and stronger, your body builds and repairs the tiny tears strength training creates in your tissues. Free radicals — normally thought of as bad guys — support these muscle changes.

“We need to micro-damage the muscle and involve other biochemical reactions, including formation of free radicals, in order to let the muscle recover,” Mankowski says.


In this case, antioxidants and their free-radical fighting powers can be a problem. Mankowski says some research on antioxidants, specifically types found in vitamins E and C, have been found to “blunt” the beneficial breakdown processes that result from exercise. He’s quick to add, however, that the research on antioxidants and exercise are mixed. In some cases, antioxidants may be helpful, but more research needs to be done to understand when and how.

During the 1980s and early 90s, one of the things researchers were excited about antioxidants and their ability to fight cancer. “There was a lot of interest in [the antioxidant] beta carotene and its anti-cancer effects,” says Gilbert Omenn, M.D., Ph.D., a professor of human genetics and molecular medicine at the University of Michigan.

Dr. Omenn says that, back then, many preliminary studies had shown beta carotene — the red-orange pigment that gives carrots and sweet potatoes their vibrant color — could stop the growth of cancer cells, and there was a widespread belief that taking beta carotene as a supplement might benefit heavy smokers at risk for lung cancer.

So he and others launched a large-scale study in which heavy smokers took a daily supplement containing 30 milligrams of beta carotene, about the amount you would find in 10 ounces of cooked sweet potato. At the same time, a similar beta carotene study was underway in Finland.

“I was able to see the results of the Finland trial confidentially, before they were made public, and they were shocking,” Dr. Omenn says. Rather than preventing cancer, smokers in the Finnish study who took beta carotene were developing lung cancer in greaternumbers than those taking a placebo.


“Our findings turned out to be the same, but were even more dramatic,” Dr. Omenn says. In his study—which he and his collaborators terminated early—a smoker’s risk for lung cancer jumped 20 percent if he took the beta carotene supplement, rather than a placebo. “It was maybe the most potent carcinogenic effect ever discovered,” he says.

What the hell was happening? “Our findings triggered new laboratory studies,” he says. Turns out, when beta carotene is oxidized in the body, its breakdown products fire up well-established cancer pathways. More recent research has also linked antioxidant supplements with a greater risk of death, potentially due to that increased cancer risk and DNA or cell damage.A

Dr. Omenn says his findings don’t suggest that eating sweet potatoes, carrots, and other whole food sources of antioxidants is dangerous. “There are many other compounds in vegetables that may balance things out, and together seem to provide a beneficial effect,” he explains. (He still eats carrots and sweet potatoes himself.)

But when it comes to supplements or other nutrition products loaded with antioxidant compounds, his beta-carotene study shows why caution is warranted. “Antioxidants need to be approached with moderation,” he says. “It’s a very American value to think that if a little of something is good, surely a lot is better, but that’s often not true.”

Mankowski echoes his point. “Anything taken in excess may not be beneficial or safe,” he says.


When it comes to the “best” antioxidants for your health, or the ideal amounts of each to take, “there is no straight answer,” he says. Your age, health status, exercise habits, and a lot else will determine whether an antioxidant is helpful or risky for you. Also, the existing research on ideal antioxidants and dosage is far from complete, he says.

Like Dr. Omenn, he says eating a balanced diet with a variety of fruits and vegetables is the best (and safest) plan. That way you’ll get a range of antioxidants from sources that have proven health perks.

“Future studies will show what combinations of compounds, doses, and exercises modalities are most effective,” he says. But until experts have sorted out the effects, those powders, pills, and cleanses that tout ultra-concentrated, uber-powerful doses of antioxidants are a gamble.


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