It’s hard to remember, but not too long ago few people had ever heard of an “antioxidant.” Today the word pops up on the labels of countless dietary supplements—and even more often in their ads and on websites—as well as on food labels. An ever-changing array of supplements claim to have the most “antioxidant power” or to be the latest “super antioxidant” or the “most potent antioxidant ever.”
It often seems that “antioxidant” no longer means simply “something that’s good for you”—but a magical compound that will fight off chronic diseases and help keep you young.
During the past decade, however, research on antioxidant supplements has yielded mostly disappointing results. Some studies have found that antioxidants can sometimes actually do more harm than good.
What antioxidants are
Antioxidants are part of the complex world of organic chemistry. To create energy, our cells take electrons from sugars, fatty acids and amino acids. The cells add these substances to other molecules, notably oxygen. The result: unstable particles that join with other elements, particularly oxygen. These unstable molecules are called free radicals. It's normal for cellular processes to create free radicals. However, there are many other causes, such as pollution, UV light, excessive heat and smoking.
Antioxidants help deactivate free radicals. They are part of the body’s orderly defense system. Some antoxidants are familiar—vitamins C and E, beta carotene and other carotenoids, and selenium. One of the biggest classes of antioxidants in foods is called polyphenols, found not only in vegetables, fruits, chocolate, tea, coffee and wine, but also increasingly in supplements. These include flavonoids such as quercetin.
What free radicals do
Free radicals do play a role in many chronic diseases. They can cause LDL (“bad”) cholesterol to oxidize, leading to atherosclerosis, heart attacks and strokes. They can damage the basic genetic material of cells in ways that may lead to cancer. They contribute to the aging process.
Free radicals may cause trouble, but they also have a role—and our own cells actually produce them. Some of our immune cells, including white blood cells, make free radicals and use them against organisms that invade the body. Free radicals are also needed for the formation of useful compounds in the body, including prostaglandins. These hormone-like substances have a variety of effects—for instance, on cell growth and pain regulation.
Antioxidants: not always good guys
Mostly antioxidants play a positive role. But in some cases, antioxidants can become what are known as pro-oxidants, which promote the formation of free radicals. Beta carotene, for example can increase the risk of lung cancer in smokers (this seems to be because it can also act as a pro-oxidant). It’s thought that very high doses of vitamin C can promote free radicals, whereas low doses quench free radicals. It’s a delicate balance.
For this reason, people under treatment for cancer are often advised not to take antioxidant supplements, which may actually interfere with radiation treatments and chemotherapy.
Where to find antioxidants
Early hopes that isolated antioxidants, such as vitamin C or beta carotene, would help prevent chronic diseases have not been borne out. This does not mean that everything we know about our basic chemistry was wrong. There are different types of antioxidants, and having enough of them and the right ones in proper proportions is essential to health. There is convincing evidence that a healthy diet rich in fruits, whole grains and vegetables—the sources of nearly all antioxidants—can help prevent many chronic diseases.
Years ago, we recommended supplementary vitamins C and E as well as beta carotene. Our Editorial Board changed its position when good studies showed that beta carotene can actually be harmful, at least to smokers. Later, we stopped recommending supplementary vitamins C and E because good studies had failed to find any benefits (and some even suggested that vitamin E could be harmful).
Foods contain a wide array of antioxidants, and it may be the combination found in foods that does the most good. Antioxidants are an essential part of the chemistry of life, but so far those sold as supplements have not lived up to their promise—and certainly not to the hype.