The antioxidant supplements beta carotene, vitamin A, and vitamin E may increase the risk of death rather than helping health, a new review suggests.

In Wednesday's Journal of the American Medical Association, researchers in Denmark concluded some of the most common antioxidants increase the risk of dying, based on their analysis of 68 studies on more than 25,000 people.

About 10 to 20 per cent of adults in North America and Europe take supplements, according to the study.
(CBC)

"Beta carotene, vitamin A, and vitamin E given singly or combined with other antioxidant supplements significantly increase mortality," Dr. Goran Bjelakovic of the Center for Clinical Intervention Research in Copenhagen and his colleagues wrote.

"There is no evidence that vitamin C may increase longevity. We lack evidence to refute a potential negative effect of vitamin C on survival. Selenium tended to reduce mortality, but we need more research on this question," the authors write.

Given that tens of thousands of Canadians take daily vitamin supplements in the hopes of preventing or slowing cancer or cardiovascular disease, the public health consequences of the findings are great, the researchers said, noting the supplements are heavily marketed.

Antioxidant activity

Antioxidants act like mops in the body, cleaning up free radicals that are thought to damage cells leading to illness.

As for why antioxidants may increase mortality, the researchers suggest it could be that eliminating free radicals interferes with a defence mechanism.

"Antioxidant supplements are synthetic and not subjected to the same rigorous toxicity studies as other pharmaceutical agents," the team concluded. "Better understanding of mechanisms and actions of antioxidants in relation to a potential disease is needed." 

Not all supplements are created equal, agreed John Biggs, a nutritional counselor in Edmonton. Biggs said he prefers supplements made from foods rather than synthetic varieties.

"If there was anything that I think this study showed it is that taking a fragmented incomplete spectrum of a man-made synthetic vitamin may not be the best thing for your health," Biggs said.

Foods best source

But the study overstates the risk of death and understates potential benefits, according to Dr. Neil Fleshner of Toronto's Princess Margaret Hospital, an expert on antioxidants and cancer.

"So you have an excess of two deaths per thousand deaths perhaps attributed to the antioxidants," Fleshner said. "And of course these are largely short-term studies and it says nothing about the other potential longer-term benefits it may have 15, 20 or 25 years down the road."

Until there is evidence of how antioxidants work or in what combinations, Fleshner does not recommend antioxidants.

Nutrition experts see the study as further proof that the best supplement is a healthy diet. Health Canada said it will review the latest study.