雅思口语准备之食物/健康--维他命的利弊

　　Once upon a time, you believed in the tooth fairy. You counted on the stability of housing prices and depended on bankers to be, well, dependable. And you figured that taking vitamins was good for you. Oh, its painful when another myth gets shattered. Recent research suggests that a daily multi is a waste of money for most peopleand theres growing evidence that some other old standbys may even hurt your health. Heres what you need to know.

　　Myth: A multivitamin can make up for a bad diet

　　An insurance policy in a pill? If only it were so.

　　Last year, researchers published new findings from the Womens Health Initiative, a long-term study of more than 160,000 midlife women. The data showed that multivitamin-takers are no healthier than those who dont pop the pills, at least when it comes to the big diseasescancer, heart disease, stroke. Even women with poor diets werent helped by taking a multivitamin, says study author Marian Neuhouser, PhD, in the cancer prevention program at the Fred Hutchinson Cancer Research Center, in Seattle.

　　Vitamin supplements came into vogue in the early 1900s, when it was difficult or impossible for most people to get a wide variety of fresh fruits and vegetables year-round. Back then, vitamin-deficiency diseases werent unheard-of: the bowed legs and deformed ribs of rickets or the skin problems and mental confusion of pellagra . But these days, youre extremely unlikely to be seriously deficient if you eat an average American diet, if only because many packaged foods are vitamin-enriched. Sure, most of us could do with a couple more daily servings of produce, but a multi doesnt do a good job at substituting for those. Multivitamins have maybe two dozen ingredientsbut plants have hundreds of other useful compounds, Neuhouser says. If you just take a multivitamin, youre missing lots of compounds that may be providing benefits.

　　That said, there is one group that probably ought to keep taking a multi-vitamin: women of reproductive age. The supplement is insurance in case of pregnancy. A woman who gets adequate amounts of the B vitamin folate is much less likely to have a baby with a birth defect affecting the spinal cord. Since the spinal cord starts to develop extremely earlybefore a woman may know shes pregnantthe safest course is for her to take 400 micrograms of folic acid daily. And a multi is an easy way to get it.

　　Myth: Vitamin C is a cold fighter

　　In the 1970s, Nobel laureate Linus Pauling popularized the idea that vitamin C could prevent colds. Today, drugstores are full of vitamin Cbased remedies. Studies say: Buyer, beware.

　　In 2007, researchers analyzed a raft of studies going back several decades and involving more than 11,000 subjects to arrive at a disappointing conclusion: Vitamin C didnt ward off colds, except among marathoners, skiers, and soldiers on subarctic exercises