Vitamin supplements taken by millions of people everyday to stave off disease and slow the aging process may increase their risk of death, media Thursday (Mar 1) quoted researchers as saying.

An international research team from Copenhagen University Hospital reviewed the published evidence on beta carotene, vitamin A, vitamin E, Vitamin C and selenium which were taken by people for the purpose to improve health and guard against diseases like cancer and heart disease by eliminating the free radicals.

However, they claimed that these supplements could cause "oxidative stress" and damage and kill off cells.

"The message is: We shouldn't be putting anything in our mouths until we know whether it works," said Christian Gluud of the Copenhagen University Hospital. "It appears as if these substances may be harmful."

The researchers looked at clinical trials involving groups of people taking vitamins, single or in combinations with other vitamins, and compared them to similar groups taking a placebo or taking nothing.

They found there was a significantly increased risk of death in people taking some vitamins-alone or in combinations. Vitamin A increased mortality risk by 16 percent. Vitamin E upped the risk by four percent and beta carotene seven percent. Selenium and vitamin C didn't show any increased risk, and selenium actually seemed to lower the risk of death.

The researchers said there were several potential reasons for these results.

One is that the free radicals that are thought to cause the oxidative stress are the byproduct rather than the cause of disease. Another is that they may play an important role in the immune system and eliminating them could be counterproductive.

The findings did not necessarily apply to antioxidants found naturally in fruits, vegetables and other foods, the researchers stressed.

The study was published in the Journal of the American Medical Association.

Editor: Wing