Researchers said taking synthetic vitamin A and E may interfere with the body's natural defences so explaining the 5% higher chance of dying early.
The scientists from Copenhagen University came to their conclusions after examining the role antioxidants had played in the deaths of nearly a quarter of a million people.
Antioxidants, which include vitamins A, E and C as well as beta carotene and selenium, mop up free radicals, which are disease-causing compounds found in the body.
The researchers theorised that in doing so the antioxidants damaged the body's defence systems.
Goran Bjelakovic, who led the study, said: "We did not find convincing evidence that antioxidant supplements have beneficial effects on mortality.
"Even more, beta carotene, vitamin A and vitamin E seem to increase the risk of death." Vitamin C and selenium had no overall effect on survival, the scientists found.
Dr. Bjelakovic said the 5% estimate was likely to be 'conservative' and the effect on health could be even more severe.
"A large number of unpublished trials on supplements may exist," his study said.
"Their results are more likely to have been either neutral or negative than to have shown beneficial effects." He stressed that the research applied to synthetic vitamins and did not mean that vitamins found in fruit and vegetables were harmful.
Ellen Mason, a cardiac nurse at the British Heart Foundation, said, "There are good scientific reasons for believing that antioxidant supplements might protect against heart disease but a number of clinical trails have failed to provide any robust evidence in favour of this. This study in fact suggests they may actually cause some harm.
"Therefore you should not take antioxidant supplements in the expectation they will protect you from heart disease.
"Fruit and vegetables contain many naturally occurring antioxidants and are great for your health." Somewhere between 80 and 160 million people in Europe and North America take additional doses of vitamins.
The Danish researchers said stopping taking the supplements could have a significant effect on public health.
The study, which examined the results of 68 previous trials, was published in the Journal of the American Medical Association.
The research subjects included both the healthy and the sick and whether supplements were taken singly or in combination.
The researchers also looked at studies where people took low and high doses.
February 28, 2007/TORONTO -- A meta-analysis undermining the benefits of antioxidant supplements in a new study published in the February 28, 2007 issue of the Journal of the American Medical Association ignores the large body of scientific evidence supporting the benefits of antioxidants, says the Canadian Health Food Association, a national trade association representing Canada's natural products industry.
"A growing number of evidence-based studies continue to show the health benefits of antioxidants and cannot be discounted. They need to be considered when drawing conclusions from this meta-analysis," says Anne Wilkie, Vice-President and Head of Regulatory Affairs, Canadian Health Food Association (CHFA.)
"The study only serves to confuse healthy consumers who may take antioxidants," she says.
The researchers themselves acknowledge their analysis of previous studies has several limitations, including combining studies where participants were vastly different from each other (healthy versus diseased populations); where dosages used varied significantly; where the length of time of taking the supplements and the follow-up differed among the trials, and the use of varying definitions of "all-cause" mortality in the trials. Meta-analyses are valuable tools when the included studies are similar in design and study populations.
"Healthy consumers should continue to rely on antioxidant supplements for the benefits they confer," says Wilkie. "This meta-analysis does not provide convincing scientific evidence that antioxidant supplements do not provide potential health benefits."
The CHFA reminds consumers that Health Canada has established monographs with dose information and indications for the antioxidants beta-carotene, vitamin A, and vitamin C and has not reported any risks in the use of these supplements. In fact, the federal government introduced the Natural Health Products Regulations in 2004 to ensure natural health products, such as vitamins, sold in Canada were safe, had evidence to support their claims and contained what was on the label.
From the March 13, 2007, Prepared Foods e-Flash