Vitamin C, known to be a DNA protecting antioxidant, is a switch hitter, also capable of inducing the production of DNA damaging compounds. Mutations caused by these compounds have been found in a variety of tumors. Such mutations can be repaired, however, and Ian Blair of the Centre for Cancer Pharmacology, at the University of Pennsylvania, cautioned that the study shouldnt be interpreted as a claim that vitamin C causes cancer. Nor does it question the wisdom of eating a balanced diet rich in fruits, vegetables, and whole grains, he said. The findings, which come from test-tube experiments (in vitro), may help explain why vitamin C has thus far shown little effectiveness at preventing cancer in clinical trials. According to the Science authors. Its possible that vitamin C isnt working in cancer prevention studies because its causing as much damage as its preventing, but thats really speculation at this point. What we can say is that vitamin C clearly doesnt work when you expect it to, and now were in a position to see if thats whats happening in vivo, (or, in living cells) Blair said. Some scientists have long recommended dietary supplements of vitamin C, particularly for treating and preventing cancer. But the supplements effectiveness has been hotly debated; with critics saying they either have no effect or that they may be harmful. The logic being used (for vitamin C supplements) is that fruits, vegetables, etc. contain vitamin C; these foods prevent cancer; thus vitamin C prevents cancer, Blair said. But our message is that its the total diet thats important, not just one antioxidant in isolation. Vitamin C is known to do beneficial work in the body, including acting as an antioxidant that disarms free radicals. These highly reactive ions are produced by the breakdown of oxygen, which occurs constantly in cells. In addition to damaging DNA directly, free radicals can also act indirectly. They act by converting linoleic acid, the major polyunsaturated fatty acid in sunflower, and safflower cooking oils, as well as the major polyunsaturated fatty acid in human plasma, into another compound called a lipid hydroperoxide. When certain metal ions are present to act as catalysts, the lipid hydroperoxides degrade further, into DNA damaging agents called genetoxins. These compounds react with DNA, switching one base for another in mutations that have been found in human tumours. Scientists, including Blair and his colleagues, have suspected that vitamin C might also be capable of making lipid hydroperoxides degrade into genotoxins, in place of the transition metal ions. To investigate, the Science authors added vitamin C to solutions of lipid hydroperoxides in the lab. They used concentrations comparable to those found in the human body, assuming a person would take 200 milligrams a day. The vitamin was more than twice as efficient as transition metal ions at inducing the formation of genotoxins, including a particularly potent variety. The researchers next step is to see whether vitamin C produces significant amounts of genotoxins in intact cells, and whether they generate cancer-causing mutations. The study explains why vitamin C has thus far show little effectiveness in preventing cancer in clinical trials.
1. Which of the following simplifies the logic of taking vitamin supplements?
A. If A and B are useful for C and D; C and D are also useful for A and B.
B. If A contains B and C contains A, then B contains A.
C. If A contains B and A is useful for C, then B is useful for C.
D. If A is not useful for B, then B cannot prevent A.
E. If A is used for C, and B is used for C, then B is used for A.
2. Which of the following can be inferred from te passage about the carcinogenic properties of vitamin C?
A. Evidence shows that vitamin C can damage DNA in normal cells and bring in cancer causing changes.
B. The clinical studies conducted confused cause with effect; vitamin C is only a catalyst in tumor formation.
C. The studies so far are misleading because their findings disprove commonly accepted hypotheses.
D. Vitamin C taken as supplements are more damaging than taken in the natural form.
E. There is some evidence to prove it, but our understanding of the harmful effects of vitamin C is incomplete.
3. Which of the following can be inferred from the passage as a measure to prevent cancer?
A. Regular intake of supplements containing vitamin C.
B. A planned diet that is completely devoid of polyunsaturated and lipid hydro peroxides.
C. Regular intake of vitamin C-rich fruits such as citrus fruits and lemons.
D. A balanced diet that is rich in fruits, vegetables, and pulses.
E. 200 milligrams of vitamin C supplement per day.
4. Which of the following is a finding of the study described in the passage?
A. Genotoxins are catalysts that prevent the repair of damaged cells in the human body.
B. Vitamin C is not very effective in preventing cancer.
C. Vitamin C doesnt have antioxidant properties when taken as supplement.
D. In normal cells mutation caused by DNA damaging compounds is rare.
E. Vitamin C does not act as catalyst in degrading hydro peroxides into genotoxins.
1-C
2-E
3-D
4-B
