(Agencies)
Updated: 2008-04-17 08:48

Vitamin supplements taken by millions of people do not increase life expectancy and may raise the risk of a premature death, according to a review of 67 studies with more than 230,000 subjects.

The review, by the Cochrane Collaboration which regularly pools data from trials to evaluate drugs and treatments, found supplements vitamin A, vitamin E and beta-carotene are detrimental to health.

In 47 trials with 180,938 people and a low risk of bias, the "antioxidant supplements significantly increased mortality", the authors wrote. When the antioxidants were assessed separately and low risk of bias trials were included and selenium excluded, vitamin A was linked to a 16 percent increased risk of dying, beta-carotene to a 7 percent increased risk and vitamin E to a 4 percent increased risk.

Evidence for vitamin C and selenium was more equivocal, suggesting there was no benefit to taking these pills compared with a placebo.

"The bottom line is current evidence does not support the use of antioxidant supplements in the general healthy population or in patients with certain diseases," said Goran Bjelakovic, who performed the review at Copenhagen University hospital in Denmark.

"There was no indication that vitamin C and selenium may have positive or negative effects. So regarding these we need more data from randomized trials."

All the supplements are categorized as antioxidants; research has suggested these chemicals underlie some of the beneficial effects of eating fruit and vegetables because they soak up harmful byproducts of metabolism which can damage cells and cause aging.

While the evidence of a beneficial effect of a diet rich in fruit and vegetables is solid, the Cochrane data suggest antioxidant supplements are either useless or detrimental.

Bjelakovic's team evaluated 67 randomized clinical trials with 232,550 subjects; 21 of the trials were on healthy subjects, while the rest tested patients with a range of diseases. The evidence suggests it would be safer to obtain the chemicals not as supplements but by eating fruit and vegetables.