Passage One

　　Questions 21 to 25 are based on the following passage.

　　For years, doctors advised their patients that the only thing taking multivitamins does is give them expensive urine (尿). After all, true vitamin deficiencies are practically unheard of in industrialized countries. Now it seems those doctors may have been wrong. The results of a growing number of studies suggest that even a modest vitamin shortfall can be harmful to your health. Although proof of the benefits of multivitamins is still far from certain, the few dollars you spend on them is probably a good investment.

　　Or at least that's the argument put forward in the New England Journal of Medicine. Ideally, say Dr. Walter Willett and Dr. Meir Stampfer of Harvard, all vitamin supplements would be evaluated in scientifically rigorous clinical trials. But those studies can take a long time and often raise more questions than they answer. At some point, while researchers work on figuring out where the truth lies, it just makes sense to say the potential benefit outweighs the cost.

　　The best evidence to date concerns folate, one of the B vitamins. It's been proved to limit the number of defects in embryos (胚胎), and a recent trial found that folate in combination with vitamin B 12 and a form of B6 also decreases the re-blockage of arteries after surgical repair.

　　The news on vitamin E has been more mixed. Healthy folks who take 400 international units daily for at least two years appear somewhat less likely to develop heart disease. But when doctors give vitamin E to patients who already have heart disease, the vitamin doesn't seem to help. It may turn out that vitamin E plays a role in prevention but cannot undo serious damage.

　　Despite vitamin C's great popularity, consuming large amounts of it still has not been positively linked to any great benefit. The body quickly becomes saturated with C and simply excretes (排泄) any excess.

　　The multivitamins question boils down to this: Do you need to wait until all the evidence is in before you take them, or are you willing to accept that there's enough evidence that they don't hurt and could help?

　　If the latter, there's no need to go to extremes and buy the biggest horse pills or the most expensive bottles. Large doses can cause trouble, including excessive bleeding and nervous system problems.

　　Multivitamins are no substitute for exercise and a balanced diet, of course. As long as you understand that any potential benefit is modest and subject to further refinement, taking a daily multivitamin makes a lot of sense.