Supplements containing antioxidants -- purported fighters of cancer and age-related cell damage -- may do little to prolong the lives of people who take them, according to a new review of published studies.
But critics of the analysis, released Tuesday by The Cochrane Library, call the review flawed, adding that antioxidants have health benefits that are not recognized by this new research.
In the review, researchers at Copenhagen University Hospital in Denmark looked at data from 67 studies on antioxidant supplements.
"We could find no evidence to support taking antioxidant supplements to reduce the risk of dying earlier in healthy people of patients with various diseases," said lead study author Goran Bjelakovic in a press release.
"The findings of our review show that if anything, people in trial groups given the antioxidants beta-carotene, vitamin A and vitamin E showed increased rates of mortality."
Bjelakovic added that there was no indication that the antioxidants vitamin C and selenium had any effect on life expectancy.
Some diet experts said the results are not surprising in light of previous findings.
"There's no good evidence that antioxidant supplements prolong life, prevent disease, etc., and this review fits with the results of the reviews of other groups," said Dr. Paul Shekelle, director of the Southern California Evidence-Based Practice Center for the RAND Corp.
But others maintained that the study took the wrong approach, possibly oversimplifying the potential effects of these vitamins.
"Lumping all antioxidants together is not fruitful from a scientific or medical perspective," said Dr. Meir Stampfer, professor of epidemiology and nutrition at the Harvard School of Public Health in Boston. "Antioxidant is a relative chemical property, and all these highly disparate nutrients have lots of different effects."
Though health experts continue to argue over the benefits of antioxidant supplements, Americans are downing vitamin pills in ever-larger numbers.
Data from the National Health and Nutrition Examination Survey suggest that about 52 percent of Americans -- about 150 million in all -- take dietary supplements on a regular basis. More than one-third take multivitamins, and nearly one in eight take antioxidant supplements like vitamin C and vitamin E.
The upshot of this popularity is a multibillion-dollar industry that has left its mark on pharmacy and grocery shelves across the country.
In recent years, however, a number of studies and reports have chiseled away at the healthy reputation of vitamin supplements.
In May 2006, the National Institutes of Health released a conference statement in which it suggested that more information would be necessary before it could recommend that Americans take multivitamins -- and, by extension, antioxidant supplements.
But more damning was a series of reviews suggesting that some antioxidant supplements could actually hasten death.
"The vitamin E review on mortality that was in the Annals of Internal Medicine in 2005 … actually concluded vitamin E was associated with increased mortality," Shekelle said. "One can argue whether or not this association was true, but at the very least the association was not the other way, towards decreased mortality."
Other reviews, published in prominent medical journals, suggested that antioxidants had no benefit for heart disease, and in certain patients even raised the risk of cancer and heart ills.
Such findings have been denounced by groups like the Council for Responsible Nutrition (CRN), a Washington, D.C.-based trade association representing ingredient suppliers and manufacturers in the dietary supplement industry.
Annette Dickinson, former president of CRN who now works as a consultant for the group, says the current review fails to take into account the positive findings of the studies it examined.
"One of the heart disease studies showed a 75 percent decrease in the risk of a second heart attack," she said. "And one of the studies on selenium was so positive that the National Cancer Institute is now suggesting a study of selenium on 35,000 men to see if it decreases the risk of prostate cancer."
Even several diet experts agreed that the design of the review may be too narrow to determine whether antioxidant supplements have other benefits unrelated to life expectancy alone.
"I have to agree with their conclusions, but I wonder about other confounders in the analysis," said Mary Beth Kavanagh, instructor in the department of nutrition at Case Western Reserve University in Cleveland. "Dietary intake of antioxidants and other nutrients is not usually studied along with the supplements. There may be synergistic effects between antioxidant nutrients and other bioactive components of food that are missed because of this."
"It's possible that the antioxidants here have their best application in the arena of prevention rather than of cure and life extension," said Keith-Thomas Ayoob, an associate professor of pediatrics at the Albert Einstein College of Medicine in New York.
For example, he said, it is possible that supplements may increase the quality of life for people with chronic conditions such as diabetes, even if they do not necessarily extend life expectancy.
"These nutrients might not make diabetes go away, but they might help you control your diabetes better, and that wouldn't come out in this study," he said.
Despite this, nutrition experts agreed that healthful food, rather than vitamin supplements, remains the best source of antioxidants for most people.
"I think the take-home message from this [review] is that there is no substitution for a well-balanced diet that includes plenty of fruits and vegetables," said Laurie Tansman, a nutritionist at the Mount Sinai School of Medicine in New York.
Ayoob agreed. "As soon as we get a study suggesting that people are healthier on vitamins, we get one that says 'no.'"
"You cannot get in a vitamin pill what you can get in a healthy diet," he said. "So the take-home point for consumers is that it's time to eat your fruits and veggies, because we do know the benefits of that with overwhelming evidence."