WASHINGTON (AP) _ The vitamin C pills taken by millions of health-conscious Americans may actually help produce toxins that can damage their DNA, a step toward forming cancer cells, a laboratory study suggests.
In a study appearing Friday in the journal Science, University of Pennsylvania researchers said they found in test tube experiments analyzing the action of vitamin C that the nutrient can act as a catalyst to help make a toxin that can injure DNA, the body's genetic code.
The findings do not mean that vitamin C causes cancer, said Ian A. Blair, lead author of the study, but the research does sound a warning about the use of vitamin C pills.
``Vitamin C can do some good things, but it can do some bad things as well,'' Blair said. ``If you really wanted to be cautious, you just wouldn't use supplementation (vitamin pills.)''
Instead of pills, Blair said people can get all the nutrients they need through a balanced diet, particularly fruits, vegetables and grains.
Balz Frei, a professor at the Linus Pauling Institute at Oregon State University, said the Blair study ``is an important finding in understanding the chemistry of vitamin C.'' He cautioned that the results come from a test tube study, which involves chemicals in glass lab dishes, and that the same action may not occur in living animals.
In the study, Blair and his colleagues analyzed the effects of vitamin C on lipid hydroperoxide, a compound produced in the body from fat in the diet. Lipid hydroperoxide can be converted in the cell into agents, called genotoxins, that can damage DNA.
Blair said his group found that vitamin C was highly efficient in converting lipid hydroperoxide into the gene-damaging toxins.
``Just because you damage DNA doesn't mean you'll get cancer,'' Blair said. ``The cell has an exquisite repair mechanism for lesions in the DNA.''
Blair said the research may explain the failure of studies that have attempted to show vitamin C can protect against cancer.
``There are two camps _ people who think vitamin C supplementation is good for you and those who think it is bad for you,'' he said. ``There is a paucity of any scientific evidence that it is really good for you.''
Vitamin C supplementation includes not just pills, but also the addition of artificial forms of the nutrient to foods, such as juices, cereals and even candies.
The popularity among health-conscious Americans for popping vitamin C pills was boosted by Linus Pauling, a Nobel-prize-winning chemist who advocated large doses of the vitamin. He routinely took 15 grams daily and was 93 years old when he died in 1994.
However, Frei, a nutrient expert at the institution named for Pauling, said such large doses of vitamin C have not been proven to be beneficial in clinical studies.
``The Linus Pauling Institute does not endorse megadoses,'' Frei said. ``Our advice is to eat a healthy diet rich in fruits and vegetables.''
Vitamin C is an antioxidant. It neutralizes oxygen free radicals, which are metabolic products in the cell that can damage DNA. Some researchers have speculated that because of its antioxidant action, large doses of the vitamin could prevent cancer, strengthen the immune system and prevent the common cold.
Clinical studies, though, have been disappointing, said Frei.
``Vitamin C does not prevent a cold,'' he said, although some studies suggest the nutrient may hasten recovery.
Vitamin C can help patients lower high blood pressure, and Frei said some studies have suggested that ``people in a disease state,'' such as an infection, may be helped by vitamin C.
Asked if healthy people benefit from vitamin C supplements, he said: ``I don't think we could say that.''
The Institute of Medicine, an arm of the National Academy of Sciences, recommends that women need 75 milligrams of vitamin C daily and 90 milligrams for men. Smokers need an additional 35 milligrams. These are levels easily achieved by a balanced diet.
Much more than that is generally useless, said Frei. A healthy body can absorb about 200 milligrams a day and the surplus is carried away with urine.