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CHICAGO - Beta carotene and vitamins A and E, antioxidant supplements taken by millions to fight disease, may actually raise the risk of death, a review of 68 studies on nearly a quarter-million people said today.
The finding drew fire from critics who said it was flawed and based largely on studies of people who were already chronically ill before they were treated with the supplements.
Tuesday's report related only to synthetic supplements and not to fruits and vegetables in everyday diets which are natural and contain less concentrated levels of antioxidants, said the study from the Centre for Clinical Intervention Research at Denmark's Copenhagen University Hospital.
While the review did not pinpoint any biochemical mechanism that may be behind the increased death risk, it may be that "by eliminating free radicals from our organism, we interfere with some essential defensive mechanisms", the study concluded.
Antioxidants are believed to fight free radicals, atoms or groups of atoms formed in such a way that they can cause cell damage.
"Beta carotene, vitamin A, and vitamin E given singly or combined with other antioxidant supplements significantly increase mortality," the study found.
It said the increased death risk is about 5 per cent higher than those not given supplements and that figure is probably conservative.
It also found no evidence that vitamin C increases longevity and though selenium tended to reduce mortality, more research is needed on that topic.
Balz Frei, director of the Linus Pauling Institute at Oregon State University, said the study and the data studied are both flawed because more than two-thirds of the previous research that was examined involved people with heart disease, cancer or other risks who were being treated to see if the supplements worked.
"This kind of approach does not work," he said.
"Over the years it has become clear from these clinical trials that antioxidants don't work in disease treatment."
The Natural Products Association, a supplement trade group, said the study "stands in stark contrast to large actual clinical studies that have not demonstrated any increased risks".
Daniel Fabricant, a vice president of the association, said reviews of existing studies, called meta-analysis, often work but in this case the process was biased because "there are many other factors that could contribute to mortality that were simply not assessed".
The study, published in this week's Journal of the American Medical Association, said that 10 per cent to 20 per cent of adults in North America and Europe -- up to 160 million people -- may consume the supplements involved.
"The public health consequences may be substantial," it said.
"We are exposed to intense marketing" which holds the opposite view of what the researchers found, it added.
"We did not find convincing evidence that antioxidant supplements have beneficial effects on mortality," concluded the study.
"Even more, beta carotene, vitamin A and vitamin E seem to increase the risk of death."
- REUTERS
