Antioxidants. Was there anything vitamin C, vitamin E, and beta-carotene couldn’t do? For years, people assumed that they could prevent anything, from cancer to heart attacks, strokes, cataracts and more. The concept was appealing: Damage caused by wayward oxygen could trigger tumors, ruin arteries, and blur vision. And safe, cheap antioxidants could flush all that damage away.
It has been a decade or two since researchers started to put antioxidants through the same rigorous tests that they use to prove other theories. The vitamins passed some and flunked others. And now, enough research has been done so far to allow us to step back and take stock of the evidence from these trials. Here’s the antioxidant story as of today.
| TOO MANY PILLS, TOO LITTLE PROOF |
"The evidence on antioxidants so far is disappointing," says JoAnn E. Manson, MD, of Harvard Medical School. "There are claims for any conceivable effect of these pills," says Walter Bortz, MD, of Stanford University School of Medicine and former president of the American Geriatric Society. "But the data are terrible. It’s a hypothesis in search of a proof," he adds.
But comes this recent piece of good news: A cocktail of antioxidant vitamins and zinc helps prevent the progression of age-related macular degeneration, a leading cause of blindness. Other studies, however, show that taking vitamins C, E, and A has little effect against heart disease or cancer and may even be harmful! In fact, says the US Food and Drug Administration (FDA), claims that vitamin C and E pills reduce many types of cancer are "inherently misleading." Last year, FDA prohibited such claims from appearing on food labels. However, experts say eating more foods naturally rich in antioxidants (such as brightly colored vegetables) does have many health benefits. Here’s what latest research says.
High doses of vitamin E block the oxidation of "bad" LDL cholesterol, which makes it less prone to stick to artery walls. But whether vitamin E actually prevents heart disease is debatable. Observational studies (where large groups of people are followed over time) have shown that taking 400 International Units (IU) a day of vitamin E is associated with a reduced risk of heart disease. But clinical trials (which actually test a supplement) find little or no cardioprotective effects.
Most recently, the Heart Outcomes Prevention Evaluation (HOPE) study, which followed nearly 10,000 men and women aged 55 and above and at high risk for heart attack and stroke, found that taking daily vitamin E supplements did not reduce the number of heart attacks or other events, compared to placebo over a four-and-a-half-year period.
A study reported last year found that antioxidant vitamins (including vitamin E, beta carotene, and selenium) can interfere with cholesterol-lowering drugs
simvastatin (Zocor) and niacin. Antioxidant supplements "have no value on their own" and "it looks like the vitamins actually interfere with the drugs’ ability to raise HDL cholesterol," states one of the study authors, B. Greg Brown, MD, professor of medicine at the University of Washington in Seattle.
Vitamin A helps regulate cell differentiation which prevents cells from becoming abnormal and, the theory goes, may help protect against cancer. But studies have failed to show any protective effect. In fact, too much vitamin A from both supplements and foods may actually increase the risk of hip fractures in post-menopausal women, reported Harvard researchers in the January 2, 2002 edition of the
Journal of the American Medical Association (JAMA). The update from the Nurses’ Health Study (which followed 72,337 nurses, aged 34 to 77, for 18 years) found those women with the highest vitamin A intake were 48 percent more likely to suffer a hip fracture than women with the lowest intake.
The higher risk was due mainly to
retinol, the most potent vitamin A component. Higher intakes of beta carotene, which is broken down into vitamin A, did not significantly raise the risk of hip fracture.
Vitamin C has been touted to prevent everything, from the common cold to cancer. But there’s little data to show health benefits from taking more than the recommended daily amount (please refer to accompanying table –
YOUR GUIDE TO ANTIOXIDANTS). A study among 20,000 men and women, aged 45 to 79, reported last year in
The Lancet found those with higher levels of vitamin C in their blood had a 20 percent lower chance of dying of cancer or heart disease over a four-year period.
But the study from Cambridge University concluded that the protective effects came from foods, not pills, and that eating just one extra serving of fruits or vegetables daily could substantially improve health.
In the end, nature’s packaging may be better than pills. An update from the Nurses’ Health Study published in the October 2001 issue of the
International Journal of Cancer found that women who eat plenty of carrots, tomatoes, and other foods high in carotene and lycopene (both antioxidants) may reduce the risk for ovarian cancer. Antioxidant supplements may not work as well as those in foods because they may not reach the part of the body where they are most needed – or, too many antioxidants may actually speed up the oxidation process.
While there are relatively few studies linking antioxidant pills to health, and several showing no benefit and even some harm, there are literally hundreds, if not thousands, of studies linking antioxidant-rich vegetables and fruits to a lower risk for heart disease, cancer, and many other illnesses. As Dr. Paul Thomas, the nutritionist-publisher of the newsletter
The Dietary Supplement, puts it, single nutrients "have such a mixed record, but green vegetables, citrus fruits, deep-orange colored produce, and all other types of vegetables and fruits have unequivocally been shown to be protective."