Antioxidants' Benefits: Mostly Hype?
There's little hard evidence that supplements help
Before it became a household word, antioxidant was just a term you might have heard in science class and long forgotten. Yet now these chemicals are available everywhere, in fruits like cranberries and pomegranates, in dietary supplements, and in the "antioxidant powerhouses" that flood our health food stores and supermarkets. The number of products making antioxidant claims rose over 300 percent between 2002 and 2006, according to the market research firm Packaged Facts. But did the idea that antioxidants improve health come from hard science or from savvy marketers of the latest health craze?
Bonus or Bogus?
The purported health benefits of antioxidants—including the prevention of cancer, heart disease, dementia, diabetes, eye disease, and even aging itself—are believed to arise from their ability to combat oxidative processes in the body. Oxidation is what makes a fender get rusty or an apple turn brown. But squeezing lemon juice on an apple keeps the fruit looking tasty: That's because antioxidants in the juice neutralize chemicals that cause the oxidation.
These chemicals are called free radicals, which are side products of normal metabolism. They can also be created by environmental factors like ultraviolet radiation or pollution. First isolated by scientists in the early 1900s, they weren't linked to health until the free-radical theory of aging was developed in the 1950s. Since free radicals are highly chemically reactive, they frantically couple with whatever molecules are nearby, destroying vital DNA or protein and causing age-related maladies. This is known as oxidative stress.
The body has its own natural defenses against free radicals, but they aren't 100 percent effective. The free-radical theory of aging suggests that antioxidants could intercept free radicals before they can do damage. When scientists figured out that some nutrients in food that are essential for human health—like vitamins A, C, and E—are also antioxidants, this supported the theory that antioxidants are good for you.
But in fact, science tells us nothing about how or even if antioxidants in food protect us from free radicals. On top of that, many people now consume far more antioxidants than food could ever provide, thanks to the popularity of dietary supplements. While numerous studies suggest that antioxidants may promote good health, many of these were done in test tubes or animals. The most thorough human trials of antioxidants have given, at best, mixed results. And at worst, some antioxidant vitamins may actually increase the risk of death. A 2007 paper published in the Journal of the American Medical Association examined the data from 68 trials comparing antioxidant supplements—like selenium, beta-carotene, and vitamins A, C, or E—with a placebo or with taking no pill at all. The researchers concluded that supplements of beta-carotene, vitamin A, and vitamin E increased the risk of dying by 7, 16, and 4 percent, respectively; selenium and vitamin C weren't shown to increase risk. Yet there was no proof that antioxidants were either deadly or beneficial.
Some scientists suspect that oxidative stress, perhaps caused by overeating, may contribute to the development of type 2 diabetes. There have been studies suggesting that taking antioxidants may help prevent diabetes, presumably by counteracting oxidative stress. But in large, long-term human trials with sophisticated controls, antioxidant supplements like beta-carotene and vitamins E and C failed to prevent type 2. More troubling, researchers have found evidence that taking selenium supplements may raise diabetes risk.
How could antioxidants turn against us like this? One possibility: "It's well known [among scientists] that oxidative stress might be good for you," according to Trey Ibeker, PhD, associate professor of bioengineering at the University of California–San Diego. A certain amount of oxidative stress, triggered by exercising or skipping a meal, may turn on pro-survival genes in the body that ward off everything from heart attacks to cancer. This may be why scientists have found that calorie-restriction diets can prolong the lives of worms, mice, and even monkeys.
A recent study by Ibeker's research group demonstrated how some oxidative stress can be beneficial. He and his colleagues exposed yeast to a small dose of free radicals, which switched on a set of genes that defend against oxidative stress. Then the same yeast were given a subsequent heavy dose of free radicals—and survived it better than yeast that hadn't been exposed to low-dose stress. "It's like how you want to get a little bit of a tan before going to Maui," says Ibeker. "That little bit of melanin in your skin keeps you from getting fried."
Another study showed how taking antioxidants in pill form may undermine the benefits of exercise in humans. In the study, men who took vitamins C and E each day during a four-week exercise program didn't improve their insulin resistance, a characteristic of type 2 diabetes. Yet those who skipped the antioxidant vitamins had less insulin resistance and, like the yeast exposed to a little stress, were more effective oxidative stress fighters.
The lesson may be that taking too many antioxidants keeps the body from getting the benefits of a little oxidative stress. "Too much is not good, and too little is not good. There is a middle ground that is healthy," says Ibeker. "All this research points to the fact that we don't understand the effects of antioxidants. There is no evidence that taking antioxidants in the amount people are [doing it] is a good thing."
Though it is unclear why, more and more studies are showing that taking an isolated antioxidant doesn't match the benefits of eating foods that contain the same antioxidant. "[Antioxidants] have such a synergistic effect. When you pull one out, you may not be pulling the right one out," says Kerry Neville, a registered dietitian and a spokesperson for the American Dietetic Association. "[An antioxidant] may need other nutrients to work in tandem with." Supplements don't necessarily provide that. "Fruits and vegetables are the best place to get [antioxidants]," Neville says. "Nature made them that way for a reason."
Even if you're starting to doubt the wisdom of taking antioxidant supplements, you certainly won't want to stop eating nutritious whole foods that are high in antioxidants. It may be that some as yet undiscovered compound in these foods is responsible for their health benefits, and you wouldn't want to miss out on whatever that is.
While the jury is out on taking supplements, these healthy choices have antioxidants in abundance
|Antioxidant||Beta-carotene||Lutein, zeaxanthin||Vitamin C||Vitamin A||Vitamin E||Selenium|
|Find it in...
||Carrots, Sweet potatoes, Spinach||Spinach, Peas, Winter squash||Orange juice, Peaches, Peppers, Broccoli||Egg, Carrots, Pumpkin, Kale||Tomatoes, Sunflower seeds, Almonds, Olive oil||Brazil nuts, Tuna, Barley|