The report relates 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.
It said the increased death risk is about 5 per cent higher than those not given supplements and that figure is probably conservative. It was reported the study found Vitamin A was the worst offender, raising the death risk by 17 per cent.
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.
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 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 Complementary Healthcare Council (CHC), which represents the industry in Australia, said the results were based on old data and included trials which allowed doses of vitamins not accepted in Australia.
CHC executive director Tony Lewis would not comment on the study's claims but said the evidence was "weak".
Australian expert Luis Vitetta, from the Centre for Complementary Medicine and Research, said the results were "very concerning" and added strength to evidence that vitamins could do more harm than good.
"There's a billion dollar vitamin industry based on this idea that people can prevent disease when they're actually just putting themselves at extra risk," said Professor Vitetta.
Australian Medical Association spokesman Chris Cain said there was really no need for anyone to take vitamin supplements unless prescribed by a doctor.
"It is important for people to take these vitamins with the advice and support of their doctor," he said.
"The reality is that if people have a healthy and balanced diet, they will get all of the vitamins they need. Of course there are special circumstances where people develop problems in metabolising vitamins, but in that case they will be prescribed them by a doctor."
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 and AAP
