http://www.sina.com.cn 2007年07月19日 18:28
The Truth of Vitamins
Britain is in the middle of a health revolution. And every day, millions of people take vitamin 1)supplements, convinced of their power to keep them healthy. But there is a growing 2)anxiety from scientists that our habit of taking large 3)doses of some vitamins could have very different 4)consequences.
Vitamins are nothing more than 5)chemicals that occur naturally in food. Our bodies cannot produce them themselves, and nearly a century ago scientists discovered just how vital they were for our health. Vitamin A, found in 6)dairy products, liver and fish prevents blindness and growth 7)deformities. Vitamin C, from oranges and other 8)citrus fruit, has all but ended 9)scurvy. And Vitamin D, found in fish, means children need no longer grow up with 10)rickets.
But 40 years ago, someone came along who would transform the world’s 11)perception of vitamins. 12)Pauling became convinced that vitamins could not only prevent 13)deficiency diseases, they could do something far, far bigger. The key, according to Pauling, was to take them in huge doses, because that could prevent you from catching the most 14)irritating of diseases, the 15)common cold. But does Vitamin C really prevent the common cold as Linus Pauling believed?
Professor Balz Frei is one of the world’s leading experts on Vitamin C. He has studied the evidence from 16)clinical trials involving thousands of volunteers from across the world, designed to 17)investigate Pauling’s claim that large doses of Vitamin C fights the common cold.
Professor Frei: I’ve looked at the evidence that Vitamin C can prevent the common cold, but for the general population there is really no evidence from scientific studies that Vitamin C can lower the 18)incidence of the common cold, or prevent it 19)in the first place. So taking Vitamin C supplements is not gonna help prevent the common cold.
20)In other words, the director of the very 21)institute set up to pursue Linus Pauling’s work, now believes that the great man was wrong.
But there is another anti-22)oxidant vitamin which is popular and about which scientists are much more 23)cautious—Vitamin A.
In vegetables, there is a chemical called 24)beta carotene which your body converts into Vitamin A. Studies have shown that people who eat a diet rich in beta carotene are much less likely to develop lung cancer. And this seemed to offer a 25)genuine breakthrough.
Demetrius Albanes is one of the leading cancer experts in America. He and his colleagues organised a study to confirm that high dose pills really could save millions of lives.
To have the best chance of seeing whether the pills really could prevent lung cancer, they were given to people most likely to develop it— smokers. It seemed that beta carotene pills, which everyone had hoped would prevent lung cancer, were having the exact opposite effect.
It was a 26)devastating result. The people taking the pill had shown an 18% increase in lung cancer.
Scientists still do not fully understand why beta carotene appears so beneficial in food, but seemed to have such a devastating effect on smokers when taken in a high dose pill. But because of these studies, in 2003, safety experts in the U.K. advised smokers not to take beta carotene supplements. And advised everyone to limit their daily 27)intake from high dose pills. These studies were a 28)salutary lesson that vitamin supplements were not just some harmless natural 29)remedy. In high doses they could have unexpected and dangerous consequences.
Until we understand more about these powerful chemicals, most doctors would advise everybody to seek advice before joining the high dose Vitamin Revolution.