The necessary yet potentially destructive role oxygen plays in life processes has been known for a long time. The farseeing French novelist and steampunk hero Jules Verne wrote in his 1865 novel From the Earth to the Moon that “oxygen...this gas without a smell, eminently vital, can cause the most serious disorders in the organism.” But the now-pervasive belief that we should consume loads of antioxidants to prevent oxidative damage caused by free radicals (in particular, those known collectively as reactive oxygen species, or ROS, which are natural byproducts of respiration) dates from the 1950s. That’s when researchers began to uncover correlations between free radicals and serious health problems such as cancer, heart disease, atherosclerosis, Parkinson's, Alzheimer’s, and age-related macular degeneration.
Early studies of the protective properties of antioxidants were exciting; a famous one showed links between high plasma levels of beta-carotene (which is converted to vitamin A in the body) with lower levels of cancer. The concept of filling in any nutritional cracks of a less-than-optimal diet with antioxidant supplements seemed to make perfect sense.
Today, according to an April 2011 National Center for Health Statistics data brief, dietary supplement use is widespread among U.S. adults ages 20 and over. The percentage of the U.S. population who used at least one dietary supplement increased from 42 percent in 1988–1994 to 53 percent in 2003–2006. That is obviously great news for the multibillion-dollar supplement industry, but how’s it working out for consumers?
As it turns out, the zealous overselling of antioxidants as a near universal cure-all isn’t backed up by the latest science. In fact, high doses of antioxidant supplements may do more harm than good, especially if you smoke.
It is true that antioxidants absorb free radicals like sheets of Bounty, "the quicker picker-upper," but the cut-to-the-chase conclusion that free radicals are bad and antioxidants are good is not. As Ben Goldacre writes in Bad Science: Quacks, Hacks, and Big Pharma Flacks, you’ll find that it’s a bit more complicated than that. Although free radicals in the wrong places can wreak havoc on the lining of your arteries and lead to heart disease, say, or damage DNA, thus leading to cancer, they can also be beneficial.
If there are some harmful bacteria in your body, Goldacre explains, “then a phagocytic cell from your immune system might come along, identify the bacteria as unwelcome, build a strong wall around as many of them as it can find, and blast them with destructive free radicals.” Talk to a cancer researcher or oncologist, and you’ll discover that radiation therapy uses free radicals to kill cancer cells, and some chemotherapy drugs rely on them as well. (That’s why, if you’re undergoing treatment, it’s imperative to let your doctor know what supplements you’re taking.)
The biggest surprise to many people, though, is that just because naturally occurring antioxidants are part and parcel of a healthful diet doesn't mean more is necessarily better. “Perhaps an excess of antioxidants is simply excreted or turned into something else,” Goldacre speculates. “Perhaps it just sits there doing nothing, because it’s not needed. After all, half a tank of gasoline will get you across town just as easily as a full tank. Or perhaps, if you have an unusually enormous amount of antioxidants lying around in your body...it does something actively harmful.”
Goldacre isn’t out on a limb here; cancer researchers have been pointing out much the same thing for some years. Our marvelously sophisticated bodies are brilliant at maintaining a balance among all the different kinds of antioxidants (the subject of last week’s column) and free radicals. In a 2006 blog post research chemist Chris Rhodes writes, “It is likely that the human body has been adapted by evolution to adjust the balance between ROS and antioxidants so finely that the intake of additional antioxidants has but a minor influence, and so the degree of oxidative damage is little reduced. In a way, it is reminiscent of the concept of ‘inbuilt obsolescence,’ that we cannot live forever and are designed not to....”
Generally speaking, people who eat a healthy diet (i.e., whole foods, which contain plenty of antioxidants as well as vitamins, minerals, fiber, and so forth) have lower risks of the diseases mentioned above; it could be because of other protective chemical compounds or possibly a synergistic mix. They also tend to make other savvy lifestyle choices: They exercise, drink alcohol in moderation, and do not smoke. But in our desire to optimize health (and maybe, just a little, not have to work so hard at those other things), we may be jamming our elegant machinery with crude fistfuls of antioxidant supplements. In most cases, it’s been proved that those high doses have shown little or no preventive or therapeutic effect. Researchers call this the antioxidant paradox.
Among the vast number of antioxidant trials that have been conducted all over the world are so-called prospective studies, which follow many people over a long period of time. The Physician's Health Study showed that beta-carotene supplementation had no effect on lung cancer or overall mortality in just over 22,000 participants followed for an average of 12 years. Those participants, however, were at a lower risk for lung cancer compared with those in two more-troubling studies, known as ATBC and CARET.
The ATBC (Alpha-Tocopherol, Beta-Carotene Cancer Prevention Study), conducted from 1985 to 1993, followed almost 30,000 Finnish male smokers randomized to receive alpha-tocopherol (vitamin E) and/or beta-carotene or a placebo. Among the findings were that the beta-carotene group had more lung cancer deaths (and more deaths from heart disease as well); the increased risks for lung cancer that occurred in those participants began to drop soon after the men stopped taking the supplement, and were similar to those of the placebo group within four years.
CARET (Carotene and Retinol Efficacy Trial), which began in 1985, followed about 18,000 American high-risk participants, both male and female, who received either beta-carotene and retinyl palmitate (vitamin A) or a placebo. The trial was halted in January 1996, twenty-one months ahead of schedule, on ethical grounds. A 28 percent higher lung cancer incidence and 17 percent higher overall mortality occurred in the group taking the vitamin supplements.
The Harvard School of Public Health has a nice roundup of studies, and in a systemic review of 78 randomized clinical trials published by the international, independent, not-for-profit Cochrane Collaboration, 296,707 randomized participants were given antioxidant supplements versus placebo or no intervention; 26 trials included 215,900 healthy participants, and 52 trials included 80,807 participants with various diseases in a stable phase (including gastrointestinal, cardiovascular, neurological, ocular, dermatological, rheumatoid, renal, endocrinological, or unspecified diseases). “The current evidence does not support the use of antioxidant supplements in the general population or in patients with various diseases,” the authors conclude.
Just last January, James Watson, co-discoverer of the double helix structure of DNA and first director of the Human Genome Project, made waves with a paper in the journal Open Biology, published by the Royal Society. “For as long as I have been focused on the understanding and curing of cancer,” Watson writes, “well-intentioned individuals have been consuming antioxidative nutritional supplements as cancer preventatives if not actual therapies.... In light of the recent data strongly hinting that much of late-stage cancer's untreatability may arise from its possession of too many antioxidants, the time has come to seriously ask whether antioxidant use much more likely causes than prevents cancer.”
Supplements have their place: If you are deficient in a vitamin (such as D) or mineral (such as iron), for instance, then by all means do as your doctor suggests and supplement your diet up to the recommended daily allowance. If you are thinking of getting pregnant, you’ll want to make sure you’re getting enough folic acid. But marketing claims to the contrary, the evidence showing that high-dose antioxidant supplements will effectively protect us against disease or the aging process is thin on the ground. Spend your money instead on a variety of whole foods, which will provide you with a wealth of types of antioxidants, along with vitamins, minerals, fiber, fats, and phytochemicals that are not necessarily antioxidants. In other words, think produce, not pills.