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Science & Technology
Vitamin C causes cancer?



Science & Technology

Corporate Profile

The key finding is that vitamin C can do good things and bad things

From Diana J. Choyce
June 25 - July 01, 2001

The value of vitamin C has been the subject of a long and heated debate in the scientific community. One of the leading scientists of the 20th century, Linus Pauling, who died at age 93 in 1994, championed it as a tool for fighting cancer. But skeptics argued that numerous studies have found that vitamin C produced no benefit in combating cancer, and that taking supplements actually could have negative consequences. A new study appears to add weight to those concerns. Researchers at the University of Pennsylvania added vitamin C, also known as ascorbic acid, to solutions of a degraded version of an important fatty acid found in blood, and found that it triggered the production of DNA-damaging agents known to cause mutations associated with a variety of cancers. Lead researcher Ian Blair of the university's Center for Cancer Pharmacology cautioned that the study was conducted in a test tube and not with living human cells or in actual people. "Absolutely for God's sake don't say vitamin C causes cancer,'' Blair said in a telephone interview. "The key finding is that vitamin C can do good things and bad things. And we've figured out what the bad ones are. In terms of the impact, I think it just redirects people's attention to the fact that you can't replace a good diet with magic bullets such as vitamin C.''

Blair said he had a hunch that vitamin C might be capable of changing lipid hydroperoxides into genotoxins. He added vitamin C to test tube solutions of lipid hydroperoxides, using concentrations comparable to those found in the human body if a person were taking 200 milligrams a day. The study found that vitamin C was more than twice as efficient as transition metal ions at inducing the formation of genotoxins, including a particularly potent variety.

Vitamin C acts as an antioxidant protecting against damage by ''free radicals'', highly reactive ions produced by the breakdown of oxygen in cells. In addition to damaging DNA directly, free radicals also can act indirectly. They begin by converting linoleic acid, the major polyunsaturated fatty acid in human blood plasma and the key polyunsaturated fatty acid in certain cooking oils, into another compound called a lipid hydroperoxide. When certain metal ions are present as catalysts, the compound degrades into DNA-damaging agents called genotoxins, which cause mutations that have been found in human tumors. "Far more caution should be taken in the use of dietary supplements and an insistence on real proof that there's a benefit before undertaking any of them,'' said Dr. Arthur Grollman, director of the Laboratory for Chemical Biology at the State University of New York at Stony Brook. "The real, serious implication is that it (vitamin C) could contribute to DNA damage that could cause cancer,'' added Grollman, an expert in cancer causes who was not involved in the study. "It just adds more evidence that there could be a significant risk to ascorbic acid.'' Blair said the study, which appears in the journal Science, may explain why vitamin C has shown little effectiveness at preventing cancer in clinical trials.

Vitamin C is a water-soluble vitamin that is important for bone and connective tissue growth, wound repair and the function of blood vessels. It is abundant in citrus fruits, green peppers, tomatoes, cabbage and potatoes. The recommended U.S. adult dietary allowance for vitamin C is 60 milligrams daily. Most supplements contain many times that amount. Dr. Garret FitzGerald, director of the University of Pennsylvania's Center for Experimental Therapeutics, pointed to evidence of a benefit from an overall healthy diet rather than taking supplements on any particular nutrient. "We have very clear evidence that eating a diet rich in vegetables and fruits is a healthy thing in terms of it being associated with a reduced incidence of cancer and, indeed, heart disease, for that matter,'' FitzGerald said. "On the one hand, I would say to people there's no evidence to stop taking vitamin C on the basis of these observations at this point in time. On the other hand, I'd say consider very carefully what the evidence is for taking vitamin C, which is nonexistent. The better part of valour is: save your money.''

But one antioxidant researcher said that while these are ''interesting'' findings from an "elegant'' study, it would be wrong to base dietary recommendations on chemistry experiments. "This is quite consistent with what we know about the chemical nature of vitamin C,'' Dr. Jeffrey Blumberg of Tufts University in Boston, Massachusetts, told Reuters Health. But, he said, there is "little evidence'' that these harmful effects of vitamin C are actually going on in the body.

What's more, a significant number of studies have shown vitamin C to either have no effect or a positive impact on DNA, according to Blumberg. "You have to be careful about using this study to make conclusions about how much vitamin C a person should consume,'' he said in an interview. "If you really have a good diet...getting about 200 milligrams of vitamin C a day...I agree,'' Blumberg said. "But, unfortunately, most people don't get that.'' The recommended daily intake for vitamin C is 60 milligrams, but Blumberg said up to about 250 milligrams can be safely absorbed and used by the body. Beyond that point, excess amounts will likely be excreted.